AN ABSTRACT OF THE THESIS OF
Timothy Seung-chul Lee for the degree of Master of Science in Environmental Science
presented on April 19, 2012
Title: Patterns of Benthic Macroinvertebrate Communities and Habitat Associations in
Temperate Continental Shelf Waters of the Pacific Northwest
Abstract approved:
Sarah K. Henkel
Macroinvertebrates constitute the backbone of megafaunal communities in benthic
ecosystems around the globe. Many macroinvertebrates have vital roles in benthic
ecosystems, ranging from enhancing habitat complexity to providing staple food sources
for other organisms. Regardless of how familiar macroinvertebrates are to the general
public, very few studies have attempted to describe benthic macroinvertebrate
assemblages across large spatial scale in the continental shelf waters of the Pacific
Northwest. This study describes different subtidal macroinvertebrate assemblages off
Washington and Oregon based on species-substrata associations and the key species that
distinguish one assemblage from another. Two data sets were used for this study:
underwater footage collected by the submersible Delta during 1993-1995 geological
surveys, and footage collected by the remotely operated vehicle (ROV) Hammerhead
during macroinvertebrate surveys in late summer 2011. Footages from these surveys were
used to document species-substrata associations and distinguish different assemblages
based on species composition similarities and dissimilarities. In addition, I determined if
a specific group of invertebrates, Asteroids (Echinodermata), were useful in explaining
different assemblage patterns, after all other environmental parameters were taken into
account. Findings of this study can be used not only to shed light on the structure of
macroinvertebrate communities in the Pacific Northwest, but also as baseline data for
future research on the direct and indirect effects of potential offshore installations on
macroinvertebrate communities across the continental shelf waters.
©Copyright by Timothy Seung-chul Lee
April 19, 2012
All Rights Reserved
Patterns of Benthic Macroinvertebrate Communities and Habitat Associations in
Temperate Continental Shelf Waters of the Pacific Northwest
by
Timothy Seung-chul Lee
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Master of Science
Presented April 19, 2012
Commencement June 2012
Master of Science thesis of Timothy Seung-chul Lee presented on April 19, 2012
APPROVED:
Major Professor, representing Environmental Science
Director of the Environmental Sciences Graduate Program
Dean of the Graduate School
I understand that my thesis will become part of the permanent collection of Oregon State
University libraries. My signature below authorizes release of my thesis to any reader
upon request.
Timothy Seung-chul Lee, Author
ACKNOWLEDGEMENTS
I sincerely thank my major advisor, Sarah Henkel, for her continuous dedication, support,
insight, guidance, and confidence towards successful completion of this project. I also
thank Bruce Menge and Sally Hacker of Department of Zoology for their additional
recommendations on making this project shine. This project was funded by the Bureau of
Ocean Energy Management and Hatfield Marine Science Center’s Mamie Markham
Research Award. I thank George Boehlert for his assistance in my graduate studies. I
thank Chris Goldfinger of College of Earth, Ocean, and Atmospheric Sciences for
allowing me to access the archived tapes of historical submersible dives. In addition, I
thank Morgan Erhardt and Chris Romsos for providing space and additional tools to
successfully complete invertebrate surveys of historical submersible dive videos. I thank
Marine Applied Research & Exploration and the crew of R/V Pacific Storm for providing
all the necessary equipment and resources for the successful completion of ROV survey
in 2011. I also thank Brian Tissot of Washington State University Vancouver for
providing his patience, enthusiasm, and thorough guidance during the substratum type
and invertebrate classification training. I thank my colleagues and friends for their
company and being always available to communicate with. And finally, I thank my
parents and my brother for their perpetuating love, support, and dedication that always
bolstered me to maintain my confidence and optimism at every obstacle.
TABLE OF CONTENTS
Page
CHAPTER I: Characterizing Benthic Macroinvertebrate Assemblages in Continental
Shelf Habitats of the Pacific Northwest .............................................................................. 1 INTRODUCTION ........................................................................................................... 2 MATERIALS & METHODS .......................................................................................... 6 Study Sites ................................................................................................................... 6 Video Analyses ............................................................................................................ 8 Segment Area and Species Density ........................................................................... 12 Statistical Analyses .................................................................................................... 13 RESULTS ...................................................................................................................... 19 Invertebrate Count Summary..................................................................................... 19 Substrata and Depth Summary .................................................................................. 19 Taxon-Substratum Association.................................................................................. 20 Taxa Composition Similarities and Dissimilarities ................................................... 26 Best Subsets of Environmental Variables ................................................................. 30 DISCUSSION................................................................................................................ 32 Community Differences across Different Substratum Types .................................... 32 Environmental Variables ........................................................................................... 42 Management Implications ......................................................................................... 45 CONCLUSION ............................................................................................................. 49 BIBLIOGRAPHY ......................................................................................................... 51 CHAPTER I FIGURES & TABLES ............................................................................. 59 APPENDICES ............................................................................................................... 78 Appendix A Table 1 Total raw count of macroinvertebrate taxa across all five sites
in the Delta and ROV stations. .................................................................................. 79 Appendix B Figure 1 Substrata % proportions across five sites. .............................. 81 Appendix C Table 1 The mean depth (meters) of all stations (n = 45) across the
Delta and ROV Hammerhead sites ............................................................................ 82 TABLE OF CONTENTS (Continued)
Page
CHAPTER II: Investigation of Key Asteroid Echinoderms in Benthic Macroinvertebrate
Assemblages ...................................................................................................................... 83 INTRODUCTION ......................................................................................................... 84 METHODS .................................................................................................................... 90 BIO-ENV with Modified Matrix ............................................................................... 90 Pearson’s Correlation Tests ....................................................................................... 90 RESULTS ...................................................................................................................... 92 Descriptive Species in the Delta Stations .................................................................. 92 Descriptive Species in the ROV Hammerhead Stations ............................................ 93 Specific Relationships with Asteroid Echinoderms .................................................. 93 DISCUSSION................................................................................................................ 95 BIBLIOGRAPHY ....................................................................................................... 102 CHAPTER II TABLES ............................................................................................... 105 LIST OF FIGURES
Figure
Page
1. Distribution of Delta (n = 21) and ROV Hammerhead (n = 24) stations in Pacific
Northwest’s continental shelf........................................................................................ 60 2. Distribution of ROV Hammerhead’s Gray Bank stations (n = 14), with tracklines
(blue) overlaid across planned lines (yellow) ............................................................... 61 3. Distribution of ROV Hammerhead’s Siltcoos Reef stations (n = 10), with tracklines
(red) overlaid across planned lines (yellow) ................................................................. 62 4. Taxon-substratum associations of Grays Bank 1994 stations surveyed by Delta in
Correspondence Analysis ordination ............................................................................ 63 5. Taxon-substratum associations of Siltcoos Reef 1995 stations surveyed by Delta in
Correspondence Analysis ordination. ........................................................................... 64 6. Taxon-substratum associations of Coquille Bank 1993 stations surveyed by Delta in
Correspondence Analysis ordination. ........................................................................... 65 7. Taxon-substratum associations of Grays Bank 2011 stations surveyed by ROV
Hammerhead in Correspondence Analysis ordination. ................................................ 66 8. Taxon-substratum associations of Siltcoos Reef 2011 stations surveyed by ROV
Hammerhead in Correspondence Analysis ordination ................................................. 67 9. Distribution of Delta stations based on taxa composition similarities and dissimilarities
on the 2-dimensional nMDS ordination plane .............................................................. 68 10. Distribution of ROV Hammerhead stations based on taxa composition similarities
and dissimilarities on the 2-dimensional nMDS ordination plane .............................. 69 11. Proportions of different substrata across Delta assemblages identified by SIMPROF
..................................................................................................................................... 75 12. Proportions of different substrata across ROV Hammerhead assemblages identified
by SIMPROF. See Table 6 for details on each assemblage’s stations. ....................... 76 LIST OF TABLES
Table
Page
1. List of taxa with highest contribution % in defining different macroinvertebrate
assemblages across the Delta stations ........................................................................... 70 2. Dissimilarity % and the contribution (C%) of five most important taxa to the
dissimilarity between any combinations of assemblages in the Delta stations............. 71 3. List of taxa with highest contribution % in defining different macroinvertebrate
assemblages across the ROV Hammerhead stations .................................................... 72 4. Dissimilarity % and the contribution (C%) of five most important taxa to the
dissimilarity between any combinations of assemblages in the ROV Hammerhead
stations .......................................................................................................................... 74 5. Top ten sets of environmental variables that are most highly correlated with the
invertebrate structure in the Delta and ROV Hammerhead stations based on the BIOENV results ................................................................................................................... 77 6. Contribution % of all sea stars across all assemblages in both Delta and ROV
Hammerhead datasets ................................................................................................. 106 7. Top five sets of environmental variables (with sea stars) that are most highly correlated
with the invertebrate structure in the Delta and ROV Hammerhead stations ............ 107 8. Pearson’s Correlation Test results between the influential sea stars and the invertebrate
taxa of interest at p = 0.05 significance level. ............................................................. 108 DEDICATION
This thesis is dedicated to the memory of my grandmother, Choi Sun-hee, who inspired
me to always be optimistic and to have tenacity to fulfill my goals.
CHAPTER I: Characterizing Benthic Macroinvertebrate Assemblages in
Continental Shelf Habitats of the Pacific Northwest
2
INTRODUCTION
Habitat heterogeneity is a major driver influencing variability in abundances and
diversity of marine species from intertidal to deep-water reefs (Benedetti-Cecchi and
Cinelli 1995; García-Charton et al. 2004). In marine environments, habitat heterogeneity
is driven by various abiotic and biotic factors, including but not limited to temperature,
depth, substratum type, and organic matter (Power 1992; Benedetti-Cecchi and Cinelli
1995; Archambault and Bourget 1996; Ramirez-Llodra et al. 2010). Habitat heterogeneity
has been attributed as a major driver of increasing complexity of biological communities;
it can support global species diversity through the increase of niche availability with
different biological and physical factors (García-Charton et al. 2004; McClain and Barry
2010). By increasing community complexity, habitat heterogeneity can influence the
formation of distinct assemblages based on different species compositions (CerameVivas and Gray 1966; Stewart 1983). In continental shelf waters, invertebrates can form
into distinct assemblages across a diverse range of habitats influenced by habitat
heterogeneity (Cerame-Vivas and Gray 1966; Stewart 1983; Weston 1988). Previous
studies on the North American continental shelf waters of the Pacific Ocean have
described different invertebrate assemblages influenced by heterogeneity of different
substrate types (Allen and Moore 1996; Allen et al. 1997; Allen et al. 1998; Stull et al.
1999; Strom 2006; Tissot et al. 2006; Hixon and Tissot 2007).
Macroinvertebrates are characterized as epifaunal species. These invertebrate are
grouped into two categories: sessile, or invertebrates with little to no motility (i.e.
sponges, gorgonians, corals), and motile, or invertebrates capable of movement (i.e. sea
3
stars, sea cucumbers, arthropods, and sea anemones) (Stein et al. 1992; Strom 2006;
Tissot et al. 2006; Tissot 2008). Macroinvertebrates are known for their vital functional
roles in marine benthic ecosystems across the globe. In some parts of the world such as
the North Sea, macroinvertebrates were observed to be critical contributors in nutrient
cycling, detritus composition, and food source for fish predators of higher trophic levels
(Reiss et al. 2009). In intertidal habitats, macroinvertebrates serve as a vital link of
energy flow between the primary consumers and large predators (Ricciardi et al. 1999).
Macroinvertebrates have also been identified as indicators of the overall productivity of
benthic ecosystems (Cusson and Bourget 2005). In addition, macroinvertebrates can play
important roles in increasing complexity of physical habitats and facilitating greater
diversity. Large sized, structure-forming macroinvertebrates such as sponges, corals,
crinoids, and basket stars have been suggested to provide shelter and additional resource
for both fish and other invertebrates by increasing the availability of microhabitats
through their large surface area for settlement of other organisms (Tissot et al. 2006).
In the Pacific continental shelf waters of North America, several
macroinvertebrate distribution studies, mainly off southern California, have indicated that
different invertebrate assemblages can be distinguished based on the physical structure of
the habitats. Habitats composed of high-relief rocks were associated with greater
densities of sessile and structure-forming macroinvertebrates including sponges and
gorgonians, which in turn attracted more macroinvertebrate species and thus enhanced
greater diversity; alternatively, low-relief habitats composed of fine sediments were
associated with motile macroinvertebrates including sea stars, crustaceans, bivalves, and
4
sea cucumbers (Allen and Moore 1996; Allen et al. 1997; Stull et al. 1999; Strom 2006;
Tissot et al. 2006). Although the sessile macroinvertebrate communities at selected sites
on the continental shelf margins off Washington and Oregon were reviewed by Strom
(2006), no studies have yet assessed the macroinvertebrate assemblages in the shelf
habitats off Washington and Oregon by encompassing an entire macroinvertebrate
community of both sessile and motile types.
Macroinvertebrates are also indicative of the general condition of benthic
ecosystems, particularly before and after effects caused by trawling, dredging, and other
anthropogenic impacts (Watling and Norse 1998; Norse et al. 1999; Hixon and Tissot
2007; Tissot et al. 2007). Due to the deficiency of information regarding
macroinvertebrate assemblages off the Pacific Northwest, and the role of invertebrates in
benthic ecosystem health, describing community patterns in macroinvertebrate
assemblages and evaluating the current status of Pacific Northwest’s inner benthic
continental shelf habitats is valuable. Furthermore, the study of benthic macroinvertebrate
assemblage patterns also can be used as baseline data for the regulation of potential
seafloor-disturbing anthropogenic activities in the Pacific Northwest and beyond
(Watling and Norse 1998; Norse et al. 1999; Strom 2006). In order to shed light on
continental shelf macroinvertebrate assemblages, I will address the following three main
objectives for this study:
i.
Describe different macroinvertebrate communities based on different substratum
types
5
ii.
Describe similarities and dissimilarities between different macroinvertebrate
assemblages
iii.
Find the appropriate set of environmental parameters that best explain the
macroinvertebrate assemblage patterns
These objectives will be addressed using 21 underwater transects surveyed by the
manned submersible Delta in early to mid 1990s, and 24 underwater transects surveyed
by the remotely operated vehicle (ROV) Hammerhead in 2011.
6
MATERIALS & METHODS
Study Sites
Historic dives of the 1990s
In the early to mid-1990s, geologists of Oregon State University surveyed the
seafloor of the Pacific Northwest’s continental shelf waters off the coast of northern
Washington to northern California. Their major objective was to study topographic
features. The geologic surveys were conducted using a manned-submersible Delta, which
was equipped with a Hi-8 camera attached on the starboard side. The camera of Delta
was equipped with two sizing lasers 20 centimeters apart. The Delta also was equipped
with sensors that continuously measured the depth (meters) and temperature (Celsius)
every second. I reviewed the historic geologic surveys that had not been previously
reviewed for invertebrate counts and identification three sites distributed across different
latitudes and a diverse range of benthic habitat structures based on substratum type, depth,
and temperature within and among sites. These three sites were Grays Bank (off Grays
Harbor, Washington; these stations were sometimes analyzed separately into Deep &
Shallow) from September 1994, Siltcoos Reef (off Charleston, Oregon) from September
1995, and Coquille Bank (off Bandon, Oregon) from September 1993 (Figure 1). A total
of 21 dives, or stations, were reviewed across these three sites: four stations at Grays
Bank Deep, two stations at Grays Bank Shallow, seven stations at Siltcoos Reef, and
eight stations at Coquille Bank. Grays Bank stations encompassed a wide depth range of
50 – 310 meters (thus the rationale for breaking the area into two sub-sites: Deep and
7
Shallow), Siltcoos Reef stations were 98 – 120 meters, and Coquille Bank stations ranged
80 – 130 meters.
2011 ROV Hammerhead Dives
From August 24 to September 3, 2011, benthic macroinvertebrates were surveyed
at two sites using the R/V Pacific Storm. The two sites were Grays Bank (off Grays
Harbor, Washington), and Siltcoos Reef (off Charleston, Oregon). For this survey, the
Grays Bank stations were selected so that they fell in an area between the two previously
surveyed areas from early 1990s (Grays Bank Deep and Grays Bank Shallow). As for
Siltcoos Reef, many of the stations overlapped with the Siltcoos Reef stations surveyed
by Delta in 1995 (Figure 1). The remotely operated vehicle (ROV) Hammerhead, a
modified deep-ocean Phantom, was used to survey habitat and macroinvertebrates at
these two sites. The Hammerhead is equipped with two cameras attached at the front of
the ROV; one faces downward and is perpendicular to the sea surface, while the other
faces outward, angled roughly 30 degrees from the dorsal surface of the Hammerhead.
Unlike the Delta, the sizing lasers on the camera facing outward are 10 centimeters apart,
while the sizing lasers on the camera facing downward are 13 centimeters apart. The
ROV Hammerhead was equipped with a CTD instrument that measured depth (meters),
temperature (Celsius), and salinity (PSU) every second. It was also equipped with a
navigation instrument that measured the latitude and longitude every second. In total,
twenty-four stations were surveyed across Grays Bank and Siltcoos Reef: fourteen
stations at Grays Bank, and ten stations at Siltcoos Reef. The Grays Bank stations
8
encompassed a depth range of 55 – 80 meters, and the Siltcoos Reef stations
encompassed a depth range of 100 – 120 meters. Each station was comprised of three
transects. Each transect was approximately 250 meters long. At each station, these
transects were separated in parallel by 250 meters apart (Figures 2, 3).
Video Analyses
I reviewed a total of 23 Hi-8 tapes that contained footage of 21 stations across
Grays Bank, Siltcoos Reef, and Coquille Bank from the historic Delta dives. I also
reviewed a total of 12 DVD discs that contained footage of 24 stations across Grays Bank
and Siltcoos Reef from the 2011 ROV Hammerhead dives. Each Delta station video was
watched three times using the following procedure:
i.
Substratum Identification: Substratum segments were identified based on the
grain size class and relief level, as proposed by Stein (1992). Each substratum
type was coded with a single letter: T for pinnacle, R for ridge rock, F for flat
rock, B for boulder, C for cobble, P for pebble, G for gravel, S for sand, M for
mud, and U for unconsolidated, or substratum unable to be classified. Pinnacles
are the largest grain size class characterized by relief ≥ 3 meters with substratum
angle ≥ 80 degrees. Ridge rock is the second largest, characterized by relief ≥ 1
meter with substratum angle 30 – 80 degrees. Flat rock is the third largest,
characterized by less than 1 meter relief and substratum angle of less than 30
degrees. Boulders are classified as 25 cm – 1 m in diameter. Cobbles are 6.5 –
25.5 cm, pebbles 2 – 6.5 cm, gravel 0.4 – 2 cm, and sand and mud less than 0.4
9
cm in diameter (sand is lighter in color than mud and usually found in shallower
waters).
Each substratum segment was coded with two letters, the first letter
indicating a primary substratum (comprising 50-80% of the segment), and the
second letter indicating a secondary substratum (comprising 20-50% of the
segment). If the substratum segment was comprised of two substrata in equal
proportions, then the segment was coded with the first letter indicating the
substratum with larger grain size. For example, if a substratum segment had equal
proportions of boulder and mud, this segment was named BM, since the boulder
has larger grain size diameter than the mud. If a substrata segment was composed
of a substratum that covered over 80% of the segment, then the segment was
coded with two same letters; for example, if mud composed over 80% of the
segment, the segment was labeled MM.
The start and end times of each substratum segment were recorded. The
start time of the segment was recorded as soon as the sizing lasers touched the
segment, and the end time of the segment was recorded as soon as the sizing
lasers touched the next different substrata segment.
ii.
Sessile Invertebrate Identification: Sessile invertebrates were identified using
color images from invertebrate guidebooks. These guidebooks include the
“Invertebrate Classification Guide and Central California Invertebrate
Guidebook” by Tissot(2008), “Marine Life of the Pacific Northwest” by Lamb &
Hanby (2005), “Brittle Stars, Sea Urchins, and Feather Stars of British Columbia,
10
Southeast Alaska, and Puget Sound” by Lambert (2007), and “Pacific Reef &
Shore: A Photo Guide to Northwest Marine Life” by Harbo (2003). In addition,
images of various invertebrates were browsed in Google search engines to
familiarize myself with the diverse morphological forms of sessile invertebrates.
Many sponges and gorgonians were extremely difficult to identify to the lowest
taxonomic classification without actual specimens, and thus were only
characterized based on their morphology (i.e., branching sponge, shelf sponge,
foliose sponge, and branching red gorgonian). Studies of identifying marine
invertebrates in the past have suggested a size of ≥ 5 cm threshold to distinguish
macroinvertebrates from micro-invertebrates (Riedl 1971; Tissot et al. 2006).
Through many hours of footage reviews, I also found the 5 cm to be a useful
threshold in determining at which minimal size can the invertebrates clearly be
distinguished, counted, and identified at the lowest taxonomic classification.
Therefore, during the footage analyses, all sessile invertebrates ≥ 5 cm were
counted and identified to the lowest possible taxonomic level.
iii.
Motile Invertebrate Identification: Motile invertebrates were identified using the
same guidebooks from the sessile invertebrate identification. In addition, the “Sea
Cucumbers of British Columbia, Southeast Alaska, and Puget Sound” by Lambert
(1997) and the “Sea Stars of British Columbia, Southeast Alaska, and Puget
Sound” by Lambert (2000) were used to accurately identify Echinoderms. Like
the sessile invertebrate identification, images of various motile invertebrates were
browsed in Google search engines to familiarize myself with the diverse
11
morphological features that each motile invertebrate species can exhibit. Some
species such as Henricia spp. and Pandalus sp. were only identified to genus,
since many species in these genera have greatly overlapping morphological
features, and are difficult to distinguish without the actual specimens to be
analyzed under microscope. During the footage analyses, all motile invertebrates
≥ 5 cm were counted and identified to the lowest possible taxonomic level.
In the Delta videos, the “on-transect” designations were used to lessen the effects of
changing transect widths by variation of seafloor elevations and the height of the
submersible off the seafloor. Determining an estimated transect width for Delta station
footage could be challenging because the camera, attached to the starboard side of the
submersible, provided an oblique view of the transect. The oblique view causes the
transect width to change with variations of seafloor relief and height of the submersible
off the seafloor (Strom 2006). For instance, if the entire screen was included in the
transect width, the actual transect width would be smaller when viewing a high-sloped
formation than a relatively flat surface. Therefore, during video analyses, the “ontransect” was defined as the seafloor that appeared below the two sizing lasers on the
screen. Thus, substratum segment identification was based on the seafloor characteristics
appearing below the lasers. Likewise, only the invertebrates appearing below the lasers
were counted and identified to their lowest possible taxonomic level. Based on the
average height of the camera off the seafloor and the distance between the sizing lasers
and the submersible, the width of transect in Delta stations was estimated at 2 meters.
12
In the ROV Hammerhead footage, both the outward and downward facing
cameras were used to identify substrata segments. Since one camera was always facing
downward at a fixed angle from the vehicle, directly facing the seafloor, all footage of the
ROV Hammerhead stations viewed by the downward-facing camera were considered
“on-transect”. While I used videos from both cameras to accurately identify the
invertebrates to their lowest taxonomic level, I used the downward camera to count the
invertebrates. Each invertebrate entry was accompanied with a time code that was used to
determine in which substratum segment a particular invertebrate was found. During the
viewings of ROV Hammerhead station footages, the protocol for substrata classification
was identical to the protocol used for Delta footages, but steps ii and iii were combined
for a total of two viewings per station. The ROV Hammerhead stations encompassed
much thinner transect swaths than those covered by Delta, thus making counting both
types of invertebrates simultaneously easier, as fewer invertebrates were encountered on
per-second basis.
Segment Area and Species Density
The Delta moved at an average speed of 0.75 knots, or 0.38 meters/second (Strom
2006). With the transect width designated as 2 meters, the substratum segment area was
calculated using the following equation:
Segment Length (meters) = Total time of the segment (seconds) * 0.38 meters/second
Density of each invertebrate species per station was calculated using the
following equation:
13
Density (number/meter2) = # (number of invertebrates on-transect) / [Length (meters) *
Width (2 meters)]
The ROV Hammerhead was equipped with a navigator beam that was used to
calculate the transect width and approximate distance traveled every second. Based on
the transect width per second and the distance it traveled from the previous second, the
transect area covered was also recorded every second. Each second’s transect area entry
recorded how much area it covered from the previous second. Therefore, the area of each
substratum segment was calculated simply by adding all area entries from one second
after the start time of the segment to the end time of the segment. The density of each
species per station was calculated simply by dividing the sum of a particular invertebrate
species count by the total station area that ROV Hammerhead covered.
Statistical Analyses
To address my objectives, I used four types of statistical analyses:
Correspondence Analysis, Nonmetric Multidimensional Scaling (nMDS), Similarity of
Profile (SIMPROF), Similarity of Percentage (SIMPER), and Biota-Environment
Association (BIO-ENV). These analyses were performed for the Delta and ROV
Hammerhead datasets separately.
My matrices for the Correspondence Analysis were composed of species densities
per each substratum type. For nMDS, SIMPROF, SIMPER, and BIO-ENV, my biota
matrices were composed of species densities per sample unit, or station. BIO-ENV also
used an environmental matrix that was composed of substrata proportion, depth,
temperature, salinity, and latitude measures per sample unit, or station.
14
Correspondence Analysis
Correspondence Analysis is an ordination method that is popular among
community ecologists and is used to determine how organisms are distributed across
ecological gradients (McCune and Grace 2002). Correspondence Analysis uses repeated
weight averages to evaluate species densities, diversity, loadings, and other scores
(McCune and Grace 2002). Unlike many statistical analyses that require the assumption
that species are normally distributed across environmental gradients, Correspondence
Analysis does not require such assumptions. Correspondence Analysis plots the sample
units and species in an ordination plane and enables the ecologists to assess the
invertebrate and sample unit gradients along two axes. Correspondence requires a matrix,
which usually consists of species abundances per habitat.
My main matrix for the Correspondence Analysis had species as the rows and
different substratum type as the columns. Each cell had the species’ density (#/m2) in the
corresponding substratum type. Five substratum-species density matrices were created,
each representing the following sites: Grays Bank 1994, Grays Bank 2011, Siltcoos Reef
1995, Siltcoos Reef 2011, and Coquille Bank 1993. Thus five Correspondence Analyses
were performed. Before running the analyses, each substratum-species density matrix
was square-root transformed to normalize the density distributions.
Nonmetric Multidimensional Scaling
Nonmetric Multidimensional Scaling (nMDS) is a popular ordination method that
is considered well-suited for biota data that are arbitrary, nonnormal, discontinuous, or
15
questionable (McCune and Grace 2002). The concept of nMDS was first introduced by
Shepard and Kruskal for psychology applications (Shepard 1962). The advantage of
nMDS is that unlike other ordination methods, it is a trial-and-error method that avoids
any assumptions of linearity among variables. Therefore, it relieves the zero-truncation
problem (unknown effects of environmental gradients on species because the species is
absent from that gradient region). The nMDS creates a 2-dimensional configuration, or
“map”, of sample units based on their similarity ranks; this configuration displays the
sample units’ association with one another based on the species composition similarities
and dissimilarities between the stations. Another special feature of the nMDS is a
measure called “stress”. Stress measures the amount of scattering, or how many
movements the data points must make in order to achieve monotonicity, a final
destination that nMDS tries to approach (McCune and Grace 2002). The higher the stress
is the greater movements that the data points in nMDS have to migrate in order to achieve
monotonicity. Therefore, a high-stress result in an nMDS test is an indicator that the
nMDS plot is dangerous to interpret, and possible data adjustments might be necessary
before running the nMDS(McCune and Grace 2002). Many biostatisticians have different
interpretations of desired stress threshold, but for this analyses, I have used the stress
ranges proposed by Clarke and Warwick (Clarke and Warwick 2001). Clarke and
Warwick suggest that a stress less than 0.3 indicate the minimal useful configuration. My
matrix for nMDS had rows representing each station, and columns representing each
invertebrate taxon. Each cell had the taxon’s density to a corresponding station, or sample
unit.
16
Two separate nMDS analyses were run to address this objective, one for the Delta
biota dataset and another for the ROV Hammerhead biota dataset. The Delta biota dataset
was composed of 21 rows, or stations, and 59 columns, or taxa, with each cell
representing each taxon’s appropriate density per station. The ROV Hammerhead biota
dataset was composed of 24 rows, or stations, and 59 columns, or taxa, with each cell
representing each taxon’s appropriate density per each station. Before running the nMDS,
each biota dataset was square-root transformed to downweigh the overly abundant
species and add more weight to less common species. The transformed data were then
converted to triangular resemblance matrices of similarities between every pair of
stations using the Bray-Curtis similarity coefficient.
Similarity of Profile (SIMPROF)
The Similarity of Profile test, commonly known as SIMPROF, is an analyses
package that is available in PRIMER 6th Version (Plymouth Routines in Multivariate
Ecological Research). SIMPROF is often used by ecologists to distinguish species
assemblages based on the similarity and dissimilarity of species compositions between
sample units. SIMPROF looks for statistically significant evidences of clusters of sample
units, and based on these evidences, it forms different sample unit groups based on their
species composition similarities (Clarke and Warwick 2001). The same biota matrices
used for nMDS were also used for SIMPROF. I used SIMPROF to address the following
objective:
17
These datasets were also square-root transformed and converted to the
resemblance matrices of similarities between every pair of stations using the Bray-Curtis
similarity coefficient. The results of SIMPROF were superimposed with nMDS by
overlaying the sample unit group symbols over the sample unit points on the nMDS 2dimensional configuration.
Similarity of Percentage (SIMPER)
The Similarity of Percentage Test, commonly known as SIMPER, is also an
analysis package that is available in PRIMER 6th Version (Plymouth Routines in
Multivariate Ecological Research). SIMPER analyzes individual species’ contributions to
distinguishing a particular sample unit group, or assemblage, from other assemblages
(Clarke and Warwick 2001). SIMPER also lists the species that contribute to dissimilarity
between every possible combination of sample unit group pairings. In every sample unit
group and every possible pair of sample unit groups, it lists the species in decreasing
order of contribution to similarities or dissimilarities. SIMPER uses the sample unit
groupings that were distinguished from the SIMPROF analysis. For each sample unit
group, SIMPER also lists the average similarity percentage to indicate the overall
similarity of species compositions between the stations within a particular group. I used
SIMPER to address the following objective:
In order to determine the species that were primarily responsible for similarities
and dissimilarities between sample unit groupings, I used a 90% cutoff of total average
similarity within stations and total average dissimilarity between stations.
18
Biota-Environment Association (BIO-ENV)
The Biota-Environment Association (BIO-ENV) is also a package available in
PRIMER 6th Version. The aim of BIO-ENV is to find a subset, or “best match” of
environmental variables that best corresponds to the patterns of species assemblage. BIOENV lists the top ten subsets of environmental variables that exhibit the highest
correlation coefficients, using the Spearman correlation method (Clarke and Warwick
2001). The same biota dataset used for nMDS and SIMPROF were used for this analysis.
In addition, the environmental matrices were also used. I ran the BIO-ENV to address the
following objective:
A total of four matrices were used for this analysis: one biota and one
environmental matrix for Delta and ROV Hammerhead each. Before running the analysis,
the biota matrices were square-root transformed and converted to the resemblance matrix
of every combination of stations using the Bray-Curtis similarity coefficient. In the
environment matrix, all substrata percentages were log-transformed to give little more
weight to the substrata proportions with very low percentages. After the substrata
percentages were transformed, the entire environmental matrix was then normalized.
19
RESULTS
Invertebrate Count Summary
A total of 76 taxa representing seven phyla were found across all six sites
surveyed by Delta and ROV Hammerhead (Appendix A). Phylum Porifera comprised the
largest percentage with nearly 40% of all invertebrates counted, followed by
Echinodermata which comprised over 30% of all invertebrates, and Cnidaria which
comprised nearly 23% of all invertebrates. The most dominant Poriferans were branching
sponges and shelf sponges, the most dominant Echinoderms were the crinoid, Florometra
serratissima, and the red sea cucumber, Parastichopus californicus, and the most
dominant Cnidarians were the branching red gorgonians and the white plumose anemone,
Metridium farcimen (Appendix A).
Substrata and Depth Summary
A total of 18 and 22 different substratum types were found in the Delta and ROV
Hammerhead stations, respectively. Overall, I observed a total of 23 different substrata
(Appendix B). At Grays Bank Deep 1994, the four dominant substrata were mud-cobble
(MC), mud-mud (MM), ridge-mud (RM), and ridge-ridge (RR). At Grays Bank Shallow
1994, the major dominant substratum type was MM. In Grays Bank 2011, the five
dominant substrata types were flat-mud (FM), mud-gravel (MG), MM, RM, and RR. At
Siltcoos Reef 1995, the three dominant substrata types were FM, MM, and RM. At
Siltcoos Reef 2011, the three dominant substrata types were MM, RM, and RR. At
Coquille Bank 1993, the two dominant substrata types were FM and RM (Appendix B).
20
The mean depth at Grays Bank Deep 1994 ranged from 167 – 204 meters
(Appendix C). The mean depth at Grays Bank Shallow 1994 only ranged from 54 – 67
meters. The mean depth at Siltcoos Reef 1995 ranged from 108 – 119 meters, and the
mean depth at Coquille Bank 1993 ranged from 85 – 125 meters. The mean depth at
Grays Bank 2011 ranged from 55 – 79 meters, and the mean depth at Siltcoos Reef 2011
ranged from 103 – 116 meters (Appendix C).
Taxon-Substratum Association
Grays Bank 1994
There were three different clusters of substrata: (1) those that were primarily
composed of mud and secondarily composed of other substratum types (mud-mud, MM,
mud-pebble, MP, and mud-cobble, MC), (2) those that were primarily composed of flat
rock (flat-mud, FM, flat-gravel, FG), and (3) those that were primarily composed of ridge
rock (ridge-mud, RM, ridge-boulder, RB, ridge-gravel, RG, and ridge-pebble, RP, ridgeridge, RR) (Figure 4).
Taxa that were associated with primarily mud group included both sessile and
motile types such as gorgonians (single stalk red, branching red, single stalk white,
branching white), Subselliflorae sea pen, the orange sea pen, Ptilosarcus gurneyi, the
glassy tunicate, Ascidia paratropa, the basket star, Gorgonocephalus eucnemis, Cancer
sp. crab, the orange tochui, Tochuina tetraquetra, sand rose anemone, Urticina
columbiana, and the sea stars (the sun star, Solaster spp., rainbow star, Orthasterias
koehleri, and the sand star, Luidia foliolata).
21
In the primarily flat rock cluster, the vermillion star, Mediaster aequalis, was
associated with FM, and five taxa were associated with FG, which were the barrel sponge,
the sunflower star, Pycnopodia sp., white-spined sea cucumber, Parastichopus leukothele,
fragile pink urchin, Allocentrotus fragilis, and the velcro star, Stylasterias forreri. There
were four taxa that appeared to be generalists between primarily mud and primarily flat
substrata group. These four taxa were the blood star, Henricia sp., the unidentified snail,
hermit crab, and the thorny star, Poraniopsis inflata.
The primarily ridge-rock cluster (RM, RB, RG, RP, RR) was associated with the
largest number of taxa relative to other substrata clusters. These taxa include sponges
(branching, upright flat, unidentified, the gray moon sponge, Spheciospongia
confoederata), the crinoid, Florometra serratissima, and the brown box crab,
Lopholithodes foraminatus.
Finally, the substratum mud-boulder (MB) and boulder-mud (BM) appeared to be
distinct in their species composition. Only one species was associated with each
substratum type: the white plumose anemone, Metridium farcimen, was associated with
MB, and the orange encrusting sponge was associated with BM.
Two taxa appeared to be generalists between flat rock group and MB. They were
the swimming anemone, Stomphia coccinea, and the fish-eating anemone, Urticina
piscivora.
22
Siltcoos Reef 1995
There were three major substrata groupings: primarily ridge rock, flat rock-mud,
and mud-mud. The primarily ridge rock substrata group included ridge-boulder (RB),
ridge-cobble (RC), ridge-mud (RM), ridge-pebble (RP), and ridge-ridge (RR) (Figure 5).
Most taxa found in Siltcoos Reef 1995 were associated with this substrata cluster. These
taxa were diverse, which included but were not limited to sponges (branching, foliose,
shelf), gorgonians (branching red, single stalk red), burrowing anemone, U. piscivora, P.
inflata, blood star, Henricia sp., cushion star, Pteraster tesselatus, the red sea cucumber
Parastichopus californicus, and the squat lobster, Munida quadrispina (Figure 5).
A few taxa were associated both with the rock cluster and the substratum flat
rock-mud (FM); these taxa included foliose sponge, branching red & white gorgonians, S.
coccinea, O. koehleri and the rose star, Crossaster papposus. Other species such as the
blood star, Henricia sp., M. quadrispina, and the single stalk white gorgonian were more
closely associated with FM. The M. farcimen, was loosely associated with FM but also
showed some affinity for mud-mud (MM). Four taxa were more strongly associated with
MM: Subselliflorae sea pen, L. foliolata, G. eucnemis, and the red octopus, Octopus
rubescens.
Finally, boulder-mud (BM) was distinct from any other substratum clusters. The
BM was found isolated at the edge of ordination plane, away from all other substrata and
species points. The only taxon that was associated with BM was Cancer crab.
23
Coquille Bank 1993
Unlike other sites, Coquille Bank had no substratum type that was so distinct from
the majority of other substrata that it was located at the far end of ordination plane
(Figure 6). However, three groups of substrata can be distinguished: the first group is
mixed with primary ridge and primary flat rock, which included flat-cobble (FC), flat-flat
(FF), flat-pebble (FP), ridge-pebble (RP), and ridge-mud (RM). A diverse array of taxa
was associated with the first group. These taxa included but were not limited to sponges
(branching, orange encrusting, upright), branching red gorgonian, U. columbiana,
Subselliflorae sea pen, F. serratissima, P. leukothele, Henricia sp., P. inflata, and C.
papposus.
The second group was composed of mud with other low-relief substrata including
boulders and cobbles, which included mud-boulder (MB), mud-cobble (MC), cobble-mud
(MC), and mud-mud (MM). Only six taxa were associated with second group of
substrata: the unidentified sponge, gorgonians (branching red, branching white, single
stalk red), Solaster spp., and P. tesselatus.
The third substrata group, ridge-ridge (RR) was closely associated with three taxa:
S. coccinea, A. fragilis and the fat thorny star, Poraniopsis jordani. Five taxa were
distribute at the far end of the ordination plane, but were more closely associated with RR
than other substrata: these were the nipple sponge, Polymastia pacifica, U. piscivora, M.
farcimen, unidentified snail, and A. paratropa. Two taxa were loosely associated with
both FP and RR: burrowing anemone and S. forreri.
24
Grays Bank 2011
The vast majority of substratum types and species were tightly associated,
forming a dense cloud (Figure 7); this dense cloud was composed of various taxa,
including the single stalk red & white gorgonians, branching red & white gorgonians,
branching and shelf sponges, O. koehleri, S. forreri, P. californicus, G. eucnemis, hermit
crab, and L. foraminatus. While the vast majority of substratum types were tightly
clustered, like the 1994 Grays Bank observations, mud mixed with grains of other size
class (i.e. boulder-mud, BM, mud-cobble, MC, cobble-mud, CM, mud-gravel, MG) was
somewhat separated from the flat and ridge-rock based substrata. The stubby rose
anemone, Urticina coriacea, U. columbiana, and M. farcimen, were loosely associated
with BM, MC, CM, and ridge-rock substrata. Cancer sp. crab was loosely associated with
both MG and ridge-rock substrata, while the scallop was associated only with MG.
The substratum gravel-gravel (GG) and mud-mud (MM) were plotted far apart
from the major cloud of substrata & species points. The only species that was loosely
associated with GG was S. coccinea, which appeared to have equally loose associations
with GG and BM. The following species were loosely associated with both MM and
ridge-rock substrata: L. foliolata, O. rubescens, T. tetraqueta, and the red ribbon worm,
Tubulanus polymorphus. The only taxon that was tightly associated with MM was P.
gurneyi. The light-edged ribbon worm, Cerebratulus californiensis, burrowing anemone,
and Subselliflorae sea pen were at the edge of ordination plane away from all substrata
types, but the substratum they were closest to was MM.
25
Siltcoos Reef 2011
There were four major substratum groups (Figure 8): one group that included mix
of substrata primarily composed of ridge rock and substrata that were also composed of
boulder. These substrata include ridge-cobble (RC), ridge-mud (RM), ridge-ridge (RR),
flat-boulder (FB), mud-boulder (MB), and boulder-mud (BM). A great diversity of taxa
were associated with this cluster, including but not limited to the sponges (branching and
shelf), gorgonians (branching white and single stalk red), U. columbiana, U. coriacea, S.
coccinea, Solaster sp., G. eucnemis, O. koehleri, slipper sea cucumber, Psolus chitinoides,
P. leukothele, and M. quadrispina.
Another substratum group was also composed primarily of ridge rock, but their
secondary substrata were smaller grain size; these substrata were ridge-gravel (RG) and
ridge-pebble (RP). The substratum mud-cobble (MC) was also closely associated with
RG and RP. Only three taxa were associated with this group of substrata. RG was
associated with A. fragilis, MC was associated with the foliose sponge, and RP was
associated with the branching red gorgonian.
Another group of substratum was composed of mud and other small grain size
class. These two substrata were gravel-mud (GM) and mud-pebble (MP). The only taxon
that was associated with this group was M. farcimen.
The final substratum type was mud-mud (MM), which appeared distinct from all
other substrata groups. The following taxa were loosely associated with MM and ridgerock substrata: Subselliflorae sea pen, orange sun star, Solaster paxillatus, L. foliolata,
26
and O. rubescens. Three taxa were only associated with MM: Pandalus sp. prawn, pink
tritonia, Tritonia diomedea, and the scallop.
Taxa Composition Similarities and Dissimilarities
Delta Stations
Most of the Siltcoos Reef and Coquille Bank stations were clustered tightly
together within each site, while the Grays Bank stations exhibited greater degree of
separation within that site compared to stations from other sites (Figure 9). The stress
value of nMDS ordination was 0.11, suggesting that this is a useful ordination without
risk of false inferences (Clarke and Warwick 2001).
Seven significantly different station groups, or assemblages, were identified based
on SIMPROF (Figure 9). No groups contained stations from more than one major site;
however, assemblage G was comprised of two Grays Bank Deep and one Grays Bank
Shallow station. Assemblage B had largest number of stations (seven Coquille Bank
stations) followed by assemblage D (five Siltcoos Reef stations). Two assemblages had
two stations each (assemblage A: GB-3417 and 3419, assemblage F: SR-3668 and 3670),
and two assemblages had one station each (assemblage C: CB-3071, assemblage E: GB3415).
Most of the highest characterizing species per assemblage, or the species with
highest within-site similarity percentage (SIMPER analysis), were sessile taxa (Table 1).
Most assemblages only had two to three taxa that together brought a within-similarity
cumulative contribution greater than 60%. Assemblage A (71.16% average similarity)
27
was mainly characterized by F. serratissima, and sponges (shelf and unidentified).
Assemblage B (70.41% average similarity) was characterized mainly by the branching
sponges and F. serratissima. Assemblage F (85.81% average similarity) was mainly
characterized by only one taxon, Subselliflorae sea pen: this taxon alone brought a
within-similarity cumulative contribution of nearly 70%. Assemblage G (47.2% average
similarity) was mainly characterized by white gorgonians (single stalk and branching)
and Subselliflorae sea pen; these three taxa together brought a within-similarity
contribution greater than 70%. Assemblage D (65.5% average similarity) was different in
terms of characteristic taxa; unlike other assemblages, the contribution % was distributed
in smaller percentages across more taxa, and thus more taxa were required to bring a
within-similarity cumulative contribution to greater than 60%. These taxa also were more
diverse; like in other assemblages, sponges (shelf and branching) and branching red
gorgonians were also characteristic of this assemblage, but motile taxa including P.
californicus, P. leukothele, and California lamb shell, Laqueus californicus were also
characteristic. Assemblages C and E were not analyzed for contributing species by
SIMPER, since they had only one station each.
Most of the taxa that contributed largely to the dissimilarities between every
possible pair of assemblages were sponges, gorgonians, crinoids, and sea pens (Table 2).
The dissimilarities between nearly all assemblage pairs were largely characterized by
sponges (branching and shelf), gorgonians (branching red, single stalk red, and single
stalk white), and crinoid, F. serratissima. G. eucnemis, additionally contributed to
dissimilarities between assemblage B and other assemblages. Additional species that
28
contributed to dissimilarity of assemblage E with other assemblages were Subselliflorae
sea pen and M. farcimen. Finally, dissimilarities between assemblage F and other
assemblages were mainly characterized by Subselliflorae sea pens, gorgonians (branching
and single-stalk red and white), F. serratissima, and G. eucnemis.
Although the majority of taxa that characterized dissimilarities were sessile types,
there were few motile invertebrates that also contributed smaller dissimilarity percentages
(Table 2). Dissimilarities between nearly all assemblage pairs were characterized by
motile taxa including M. aequalis, P. californicus, P. leukothele, L. californicus, and L.
foliolata (Table 2).
Most of the average dissimilarity between every possible pair of assemblages was
greater than 70%, except for the four assemblage pairs: A & D, B & C, B & D, and C &
D (Table 2).
ROV Hammerhead Stations
The majority of Siltcoos stations were closely clustered together while the Grays
Bank stations showed a greater degree of dispersion (Figure 10). This nMDS
configuration had a stress of 0.08, which is less than 0.3, suggesting that this is a useful
ordination without risk of false inferences (Clarke and Warwick 2001).
Seven significant assemblages were identified based on SIMPROF (Figure 10).
Three assemblages were identified solely within the Grays Bank stations, and three
assemblages were identified solely within the Siltcoos Reef stations. The final group had
three Grays Bank stations and one Siltcoos Reef station.
29
All assemblages were largely contributed by sponges and gorgonians, along with
few sea stars and sea cucumbers (Table 3). Assemblages C, E, and F (73.17, 78.13,
74.81% average within-group similarity respectively) each were largely characterized by
a mix of sponges (branching and shelf sponges), gorgonians (branching red, branching
white, single stalk red, single stalk white), P. californicus, blood star, Henricia sp., and
the L. foliolata.
Assemblages D and G (74.09 and 37.86% average within-group similarity
respectively) were slightly different from other assemblages in terms of major
characteristic taxa (Table 3). Assemblage D was almost exclusively characterized by
gorgonians (branching red, branching white, single stalk red, single stalk white),
Subselliflorae sea pen, and M. farcimen. These six taxa together brought a cumulative
within-group similarity greater than 70%. Assemblage G on the other hand had much
fewer taxa that brought cumulative within-group contribution. While other assemblages
required at least six to seven taxa to bring cumulative within-group similarity greater than
70%, assemblage G required only four taxa to bring its cumulative within-group
similarity to this level. Four taxa contributing to greater than 70% within-group similarity
in assemblage G were Subselliflorae sea pen, branching white gorgonian, S. coccinea,
and L. foliolata.
Aside from sponges (branching and shelf) and gorgonians, other sessile and
motile taxa also contributed to characterizing each assemblage with smaller within-group
similarity percentages (Table 3). These include Mycale sp. sponge and the funnel sponge,
30
Semisuberites cribrosa, U. columbiana, U. coriacea, S. forreri, P. tesselatus, and the
giant pink star, Pisaster brevispinus.
Assemblages A and B were not evaluated by SIMPER because they each had only
one station (Figure 10, Table 3).
Most of the dissimilarities between assemblages B, C, D, E, F, and G and other
assemblages were largely characterized by sponges (branching and shelf), gorgonians
(branching red, branching white, single stalk red, single stalk white), M. farcimen,
Subselliflorae sea pen, P. californicus, and M. aequalis (Table 4). However,
dissimilarities between assemblage A and other assemblages were most characterized by
prawn Pandalus sp. Pandalus sp. was also a large contributor to dissimilarities in other
assemblage pairs, including assemblages C & B, D & B, and F & B. M. quadrispina, also
contributed largely to dissimilarities in two assemblage pairs (D & B, F & B).
Of 21 possible different pairs of all assemblages, 14 pairs had average
dissimilarity under 60%, while the remaining seven pairs had higher average dissimilarity
ranging from 61 to nearly 85% (Table 4).
Best Subsets of Environmental Variables
Delta Stations
The highest correlation between the macroinvertebrate community structure and
the environmental variables was shown when only the proportion of mud-mud (MM)
substrata was used (r = 0.799) (Table 5). The correlation dropped a bit when latitude was
added (r = 0.779), and dropped even further when the proportion of ridge-mud (RM) was
31
added (r = 0.768). Replacing latitude with depth in the previous subset brought
correlation down further (r = 0.76).
ROV Hammerhead Stations
The highest correlation between the macroinvertebrate community structure and
environmental variables was shown when three variables were in a subset: gravel-gravel
and ridge-mud proportions and temperature (r = 0.789) (Table 5). The correlation
dropped very slightly when temperature was replaced with latitude (r = 0.788). The
addition of ridge-ridge proportion (RR) to the first variable subset also brought
correlation down slightly (r = 0.784), and replacing this temperature with latitude also
decreased correlation coefficient as well.
32
DISCUSSION
Community Differences across Different Substratum Types
Throughout the five sites, two major communities can be distinguished based on
the taxon-substratum associations and the assemblage descriptions: high-relief substratum
types and low-relief substratum types. However, upon closer analysis of high-relief
substratum types, finer details of taxon-substratum associations showed that although
many of the taxa overlapped greatly across the majority of flat rock and ridge rock
substrata, occasionally some taxon-substratum patterns showed that taxa associated with
flat rock substrata were different from taxa associated with ridge rock substrata. Within
low-relief substratum types differences were observed between communities associated
with substrata primarily composed of mud and those primarily composed of gravel.
Further,, the communities associated with substrata primarily composed of mud also were
able to be distinguished among mud mixed with small grain size rocks, pure mud, and
boulder-mud.
In most cases, the majority of macroinvertebrate taxa were associated with highrelief substratum types. Substratum types composed primarily of ridge rocks were
associated with the most diverse array of sessile and motile taxa, including various forms
of sponges, gorgonians, crinoids, white plumose anemones, sea stars, and sea cucumbers.
Substratum types primarily composed of flat rocks usually were associated with lower
taxa diversity; unlike substratum types primarily composed of ridge rocks, the only
sessile invertebrates associated with flat rocks were gorgonians. Aside from gorgonians,
33
most species associated with flat rocks were sea stars, sea cucumbers, white plumose
anemone, and occasionally crustaceans. The great diversity of taxa associated with ridge
rock substrata can perhaps be attributed to the physical complexity in primarily ridge
substrata, because more physical complex substrata can bring greater variation in depth,
temperature, nutrient transport, and can also be composed of variety of different elements
(Taylor and Wilson 2003). Furthermore, these high-relief substrata can provide stable
surfaces to support large diversities of sessile invertebrates, which, in turn, can also
facilitate greater diversity and increase niches for other invertebrates by increasing the
physical complexity (Tissot et al. 2006). Sessile invertebrates such as sponges,
gorgonians, crinoids, and basket stars can provide shelter, refuge, and spawning grounds
for other invertebrates, but also provide microhabitats for microinvertebrates, thereby
increasing resource supply to host greater macroinvertebrate diversity (Strom 2006). The
lower sessile invertebrate diversity in primarily flat rock substrata compared to primarily
ridge rock substrata can be attributed to the overall lower physical complexity that
primarily flat rock substrata have, which in turn would provide fewer niches than
primarily ridge rock substrata, thus supporting less sessile invertebrate diversity. Motile
taxa may be better adapted in flat rock substrata than sessile invertebrates because the
motile invertebrates have ability to move between substrata of different relief, and thus
possibly have the advantage of seeking resources from other substrata types if the
conditions in flat rock are not favorable. The association between flat rocks and
gorgonians also corresponds with the findings by Strom (2006) and Tissot et al. (2006),
34
which suggests that gorgonians may be well-adapted to lower-relief habitats, as long as
they provide hard surfaces for gorgonians to attach to.
Although most sites showed similarity of taxon-substratum associations within
ridge rock substrata and flat rock substrata independently, one of the sites, Coquille Bank
1993, appeared to be unique because its flat-pebble (FP) and ridge-ridge (RR) appeared
to be distinct from other primarily flat and ridge rock substrata based on taxonsubstratum associations with most of the invertebrates associated with FP and RR being
motile types.
Another site that appeared to be unique was Siltcoos Reef 2011, because its ridgegravel (RG) and ridge-pebble (RP) appeared to be dissimilar from other flat rock and
ridge substrata based on its taxon-substratum associations. The uniqueness of RG and RP
from other ridge substrata such as RC, RM, and RR may be attributed to the grain size of
gravel and pebble. When these substrata are exposed to increasing current velocity and
volume of water flow, certain volumes of pebble and gravel may be transported and
carried across the ridge rock layer. The fragile pink urchin, Allocentrotus fragilis, was the
only taxon that was associated with RG, possibly because it can avoid unfavorable
conditions (i.e. conditions which gravel and pebble are transported across the reef in
increasing volumes) through its motility. Branching red gorgonian was the only taxon
associated with RP, possibly because they are more tolerant against the exposure to the
movement of pebbles, whereas other sessile invertebrates might be more susceptible to
damage. Perhaps the substrata RC and RM were not shown to be similar to RG and RP in
terms of taxa associations, because the cobble might be too heavy to be transported by the
35
currents, and RM’s mud grains are possible too small to inflict damages on sessile taxa as
these grains are transported across the reef.
Across most of the sites, the substratum type mud-mud (MM) was particularly
unique in its taxon-substratum association from other substratum types. MM was usually
associated with very few taxa, most of which were motile. Few sessile invertebrates were
observed on this substratum likely because of a lack of hard substrate for attachment –
this is probably the main reason there are only motile, rather than the idea that motile can
move to find favorable places. Pure mud has very low physical complexity and thus very
low variation of depth and nutrient transport, which would provide fewer niches than
high-relief substrata would, thus preventing pure mud from supporting large
macroinvertebrate diversity. Many of macroinvertebrates that have advantage in pure
mud would be motile, since these invertebrates have the capability to move between pure
mud and other substratum types to seek favorable conditions if the conditions in pure
mud become unfavorable. Most of the motile taxa I observed in mud habitats included
the sand star, Luidia foliolata, the red octopus, Octopus rubescens, Cancer sp. crab, and
in Siltcoos Reef 2011 particular, the Pandalus sp. prawn. However, one sessile
invertebrate that was unique to MM was the Subselliflorae sea pen. These sea pens may
provide pivotal roles in pure mud substrata because their sessile structure (composed of
long stalk and peduncle buried in sediment) may enhance physical complexity in a
habitat where naturally low physical complexity exists; furthermore, their filter-feeding
strategies may allow them to retain nutrients from currents and gather plankton near the
sediment, thus attracting motile invertebrates in a habitat of low niches availability
36
(Tissot et al. 2006; Greathead et al. 2007). One of the motile invertebrates that was
usually strongly associated with pure mud was L. foliolata, which may find pure mud
conditions most favorable since it often relies on its burrowing abilities to capture
infaunal invertebrates (Mauzey et al. 1968; Lambert 2000).
One unexpected finding was the association between the basket star,
Gorgonocephalus eucnemis, and pure mud at two sites, Grays Bank in 1994 and Siltcoos
Reef in 1995. G. eucnemis are known to be structure-forming species due to their large
size, sessile feature, and complex branching morphology. Past study of the continental
shelf margins off southern California found that G. eucnemis usually were associated
with high-relief rocky substrata where more physical complexity exists (Tissot et al.
2006). My observations suggest that perhaps G. eucnemis also may have capabilities to
adapt to fine-sediment habitats where there is low availability of hard rocky surfaces. The
expansion of G. eucnemis across the mud substrata may add physical complexity in these
regions where naturally low physical complexity exists; this can enhance greater habitat
heterogeneity, which would attract greater diversity of macroinvertebrates.
Mud mixed with other substrata such as gravel, pebble, and cobble were also
dissimilar from other substrata based on taxon-substratum associations. Mixed mud
substrata were usually associated with motile invertebrates including sea stars, anemones,
and crustaceans. This also suggests the possibility that motile invertebrates are better
adapted in these low-relief mixed mud substrata since they have the ability to move
around between different substrata, and that these low-relief mixed mud provide few
niches to support large sessile invertebrate diversity. However, the two sites Grays Bank
37
1994 and Coquille Bank 1993 showed that gorgonians also were associated with lowrelief mixed mud substrata; similar to the gorgonians’ association with flat rock substrata;
it is also possible that gorgonians may be adapted to these low-relief mixed mud substrata
since these habitats do provide limited hard surface for them to attach. This could
indicate that gorgonians may be the most generalist of all sessile macroinvertebrates
encountered in this study.
One unique observation with mixed mud substrata was at Siltcoos Reef in 2011.
The substrata mud-cobble (MC) and mud-pebble (MP) were associated with foliose
sponge and the white plumose anemone, Metridium farcimen respectively. While
gorgonians were suggested to be the sole sessile invertebrate type to be associated with
mixed mud substrata across all sites, the foliose sponge’s associations with MC at
Siltcoos Reef in 2011 suggest that foliose sponge also may have the ability to colonize
moderate-size grains in low-relief mud substrata. However, since this was observed in
only one site, this result cannot be inferred to the potential behavior of foliose sponges in
other sites. The association between M. farcimen and MP could also suggest that they
may adapt well with pebble substrata aside from boulder and other high relief substrata.
The observations at two sites: Grays Bank in 1994 and Siltcoos Reef in 1995
showed that substrata composed of mud and boulder can be very dissimilar from other
substrata based on taxon-substratum associations. M. farcimen and the orange encrusting
sponge were associated with boulder-mud substratum at Grays Bank in 1994, while
Cancer sp. was only associated with boulder-mud substratum at Siltcoos Reef in 1995. M.
farcimen is particularly known for its large size and very dense colonies (Tissot 2008),
38
which would also help this species to outcompete other sessile invertebrates, while the
Cancer sp. may have been associated with boulder because it may have been seeking
boulders for shelter, and may be aggressive enough to outcompete other
macroinvertebrates. However, these unique boulder observations were in only two sites;
the boulder substrata at Siltcoos Reef in 2011 appeared to be very similar to other flat and
ridge rock substrata, suggesting that boulders may also have enough niches to support
large diversity of other macroinvertebrates. The boulder in Siltcoos Reef 2011 may have
appeared to be similar to other flat and ridge rocks because of the close proximity
between flat and ridge rocks and boulders. Thus, the uniqueness of boulders in Grays
Bank 1994 and Siltcoos 1995 cannot necessarily be extrapolated to the uniqueness of
boulders in other sites of the Pacific Northwest’s continental shelf.
According to the observations at both Grays Bank and Siltcoos Reef in 2011,
gravel appeared to be very dissimilar from other substrata in terms of taxon-substratum
associations. At Grays Bank in 2011 pure gravel was solely associated with the
swimming anemone, Stomphia coccinea, while the gravel-mud (GM) at Siltcoos Reef in
1995 was solely associated with M. farcimen. Pure gravel represents a substratum type
that can support very few macroinvertebrate taxa; this is possibly due to the gravel being
easily prone to frequent topographic changes caused by current patterns, which would
cause rapid changes in hydrostatic pressures (Grant 1981). Thus, it may be that only the
macroinvertebrates that can adapt to such rapid environmental changes can survive.
Anemones are known to rely on attachment to gravel for protection against desiccation
(Hart and Crowe 1977). S. coccinea may be a species that relies on these gravel beds for
39
survival and possibly have adaptation strategies that other invertebrates lack against a
rapidly changing environment. As discussed earlier, M. farcimen have tendency to form
into very dense colonies that would exclude other sessile invertebrates from colonizing,
thereby facilitating reduction of macroinvertebrate diversity where they are present such
as in the GM observed at Siltcoos Reef in 1995..
The final macroinvertebrate communities that can be described from the
observations of these five sites were composed of generalists. These were motile
invertebrates, and they were observed to be generalists between different relief levels of
high-relief substrata, and also between pure mud and high relief, and pure gravel and
high-relief. Between flat and ridge rock substrata, the generalists were largely composed
of various sea stars, which suggest that many of these species may use their motile ability
as advantage to seek new resources between flat and ridge rock substrata. Some of these
generalists were anemones, including the fish-eating urticina, Uriticina piscivora, and the
burrowing anemone; anemones are preyed on by sea stars (SUND 1958; Houtman et al.
1997), and this suggest the possibility that anemones are also migrating between flat and
ridge rock substrata to seek additional shelter to avoid predation. The generalists between
high-relief substrata and fine-sediment substrata (mud, gravel, etc) were few but included
O. rubescens, the orange tochui, Tochuina tetraquetra, and the pink tritonia, Tritonia
diomedea. The nudibranchs T. tetraquetra and T. diomedea are predatory and may be
expanding their prey options between those available in fine-sediment substrata and highrelief substrata or to avoid competition with other predators, such as sea stars, in one
substrata or the other (Mauzey et al. 1968). O. rubescens may be taking advantage of
40
their agile behavior to seek crustaceans and other prey between fine-sediment and highrelief (Laidig et al. 1995). One species that appeared to be a generalist between GG and
mixed mud substrata was S. coccinea. S. coccinea may be dependent on mixed mud
substrata because those substrata are more heterogeneous and thus provide more
abundant prey sources, but also putting the S. coccinea at the risk of predation. When
there’s a predation risk, S. coccinea can elicit a swimming response (SUND 1958; Ross
and Sutton 1964). With this behavior, S. coccinea may be seeking refuge in GG, where
no other macroinvertebrates can adapt.
Summary
Broadly, two major groups of substrata were observed to host different
macroinvertebrate communities: high-relief substrata (composed of flat rock and ridge
rock), and fine-sediment substrata (composed of mud, gravel, pebble, cobble, and
boulders). It was observed that often, the high-relief substrata were associated with a
diverse array of sessile taxa, including crinoids, sponges, and gorgonians. In turn, the
sessile taxa appeared to enhance structural complexity, because a large variety of motile
taxa were often associated with these high-relief substrata. However, a closer analysis
showed that the communities of these sessile invertebrates sometimes differed slightly
between ridge-dominated and flat-dominated substrata. While most of the sponges were
associated with ridge-dominated substrata, gorgonians, on the other hand, were more of
generalists since many were also associated with flat rock dominated substrata covered
with fine sediment to the low-relief mixed mud substrata. From these results, a future
41
analysis could survey the high-relief substrata stations and other rocky habitats to mainly
compare the assemblages based on level of relief.
The fine-sediment substrata were often observed to be associated with motile taxa,
including but not limited to sea stars, crustaceans, and molluscs. While most of these
motile taxa overlapped between different types of substrata mixed with mud and other
grain types (gravel, pebble, cobble), two types of mud substrata, the pure mud (MM) and
boulder-mud (BM) often appeared to be unique from other fine-sediment substrata in
terms of their taxa association. In addition, sedimentary substrata composed of gravel
were also unique. While mud was often associated with Subselliflorae sea pen colonies
along with few other motile taxa, gravel and boulder were usually associated with no
more than one taxon. From these findings, a future step could aim to focus on surveying
macroinvertebrates in fine-sediment substrata by covering a wide array of grain sizes
from mud to boulder to observe the macroinvertebrate community patterns in larger
spatial scale.
The final conclusion of these taxon-substrate associations was that there usually
were groups of taxa that were generalists across different substrata groups. Some species
were generalists between MM and ridge-dominated substrata, while some were
generalists between flat-dominated and ridge-dominated substrata. However, most of
these generalists had one thing in common: they were motile. This finding brings a theory
that motile invertebrates may be more advantageous for the success of future
communities, since they can migrate to avoid unfavorable conditions but also can expand
their populations to ensure that adequate progenies survive for subsequent generations.
42
Environmental Variables
Delta Stations
In the Delta stations, the availability of pure mud (MM) and ridge-mud (RM)
were associated with an environmental variable subset that had highest correlation with
macroinvertebrate community structure. The availability of pure mud and RM suggest
that in the Delta stations, these two substrata types could be the most significant type of
all substrata that distinguished different invertebrate communities based on their
proportions. Pure mud and RM may have highest correlation because they comprise the
largest proportion of all substratum types across all seven assemblages. However,
according to the community descriptions across different substratum types, pure mud was
described to be unique from other substrata based on the types of macroinvertebrates it
was associated with, and perhaps this uniqueness that makes pure mud could be a
possible reason why proportion of pure mud was highly correlated with
macroinvertebrate community patterns. RM was highly correlated with macroinvertebrate
community patterns, which indicates the possibility that many sessile invertebrates could
prefer high-relief rocky habitats covered by fine sediments such as mud; as suggested by
Strom (2006), some sessile invertebrates may prefer these rocky habitats rather than
rocky habitats without any fine sediment cover, since there may be greater food
availability for invertebrates; sessile invertebrates such as gorgonians may prefer these
habitats because their drifting prey may also get trapped by sediment (Strom 2006). In
addition, sediment cover could also indicate presence or absence of strong currents; rocky
43
habitats with no sediment cover might be indicative of fast currents, which could hinder
the stability and survival of sessile invertebrates, while a thin layer of sediment might be
indicative of slower water movement. Furthermore, RM might have been highly
correlated because it was also associated with a large variety of taxa, both sessile and
motile, suggesting that its proportion can determine differences of macroinvertebrate
communities based on diversity.
Latitude was also considered to be an important environmental variable,
suggesting that macroinvertebrate communities in Pacific Northwest’s continental shelf
do vary by different latitudes. This was likely apparent since the Delta stations were
either off Grays Harbor Washington or off the coast of southern Oregon.
In addition, the depth was also considered to be a correlated variable, although
using the depth brought the correlation down. Depth was probably shown as an important
variable simply because the depth range in Grays Bank Deep stations varied greatly,
ranging from 50 – 310 meters, whereas the Siltcoos Reef and Coquille Bank stations had
depths ranging from 80 to 130 meters. Thus, the depth might have been displayed
because it helps distinguish the community in Grays Bank Shallow or Deep from the
communities in other sites.
ROV Stations
In the ROV Hammerhead stations, the proportion of pure gravel (GG) and ridgemud (RM) were associated with an environmental variable subset that had highest
correlation with macroinvertebrate community structure. This indicates that between the
44
stations in Grays Bank and Siltcoos Reef conducted by ROV Hammerhead, the
proportion of pure gravel and RM may be able to distinguish different communities more
significantly than other substrata types. Pure gravel likely had high correlation with
community differences because the community in pure gravel was unique, and unlike any
other; it was only associated with one taxon, S. coccinea, and no other substrata types
were only comprised of these anemones. The RM was possibly selected for similar
reasons with the RM in Delta stations.
Results showed that temperature and latitude are interchangeable, since the
correlations changed very little when a temperature or latitude was replaced by one
another; this is likely due to the strong correlation between latitude and temperature in
these sites, which are so far apart. Temperature was possibly shown as an influential
variable, because subtle temperature changes may affect sessile invertebrate survival.
Sessile invertebrates such as corals have been long identified to be susceptible to high
mortality rates caused by high temperatures (Glynn and D’croz 1990). Other
invertebrates such as gorgonians are known to be sensitive to temperature changes, since
rise in temperature would stress the cells to the extent that they would not able to produce
antifouling substances, and thereby leaving them vulnerable to predation (Cerrano et al.
2000). However, temperature was probably shown simply because temperature is
strongly correlated with different latitudes. The great difference of latitude between
Grays Bank stations and Siltcoos Reef stations could be why the latitude was also shown
as an influential variable. Latitude is also known to be correlated with different
phytoplankton productivities (Ricciardi et al. 1999). Thus, the difference of communities
45
between Grays Bank and Siltcoos Reef could also be attributed to the effects of different
phytoplankton production that all invertebrates of every trophic level would ultimately
depend on for survival.
Management Implications
Two studies set 15 years apart can be used to look at changes in invertebrates and
considered in light of management changes. The 2011 survey sets a baseline for
evaluating effects of future management decisions, since it provides the most recent data
of macroinvertebrate community descriptions in the Pacific Northwest’s continental shelf
waters.
Many studies assessing anthropogenic impacts on benthic macroinvertebrates
have been associated with trawling activities. Trawling equipments have been known to
inflict long-term damages in high-relief environments by destroying slow-growing corals
and gorgonians, thus reducing community complexity. Watling and Norse (1998) have
compared this with the analogy of cutting down mature hard-growth trees in old forests;
as the recovery of these deforested habitats will take years to centuries for full recovery,
the same could be held true for benthic macroinvertebrate habitats. The 1998 gear
restriction regulations (65 FR 221) placed limitations on types of trawl gear in the
continental shelf waters to avoid damaging sessile invertebrates in rocky habitats, raising
a hope that the complex communities of hard rocky habitats are protected from
anthropogenic disturbances (PMFC 2000); however, this gear restriction did not mention
anything about low-relief fine-sediment habitats being potentially protected from
46
trawling activities, suggesting that if such activities are taken place in these low-relief
habitats, the low-relief fine-sediment substrata may be at a greater risk (Bellman et al.
2005; Strom 2006).
The ROV Hammerhead surveys provide the most recent data of
macroinvertebrate communities on the Pacific Northwest continental shelf. Unlike the
historic Delta surveys, huge abundances of gorgonians were found in the ROV
Hammerhead stations, and these were not just restricted in high-relief substrata but also
lower relief covered by sediments. Gorgonians are known to be slow-growing and fragile
and provide additional resources for other invertebrates by providing shelter, food, and
microhabitats. Although the 1998 gear restrictions may provide gorgonian habitats with
better protection from anthropogenic seafloor disturbances, nevertheless due to fragile
state of gorgonians, it is important that habitats with assemblages characterized by
gorgonians are described as accurately as possible to improve management decisions
(Etnoyer and Morgan 2007).
In addition, many Subselliflorae sea pens were found in fine-sediment substrata
that were mainly composed of mud in both Grays Bank and Siltcoos Reef. Sea pens were
also suggested to be slow-growing and are highly sensitive to trawling and other bottomdisturbance activities (Strom 2006; Greathead et al. 2007; Tissot et al. 2007). Sea pens
are also considered a critical component of low-relief fine sediment habitats because
these regions naturally have low physical complexity, but the colonies of sea pens may
enhance structure and provide microhabitats, thereby serving important function in these
habitats (Strom 2006; Tissot et al. 2006). These important functions of sea pens and the
47
possibilities of trawl usage in low-relief habitats off Oregon and Washington suggest that
the healthy sea pen colonies observed in Grays Bank and Siltcoos could be susceptible to
long-term damage if such activities are taken place as Tissot et al. (2007) observed
absolutely no sea pens in trawled regions in their Coquille Bank study from 1990s.
Aside from trawling, the continental shelf habitats composed of fine sediments are
increasingly being considered as suitable regions for development of offshore wave
energy. Little is known about the direct and indirect effects of the offshore wave energy
installations on marine environment, but past studies of effects of offshore installations
such as oil platforms have indicated that these installations can affect macroinvertebrate
communities locally by providing surface for fouling invertebrates to establish, and in
some cases, facilitating species invasions (Page et al. 2006). While these installations
could protect a particular region from fishing and trawl-related activities, they would
result in other alterations to the habitat such as increasing the physical complexity since
the offshore installation device could act as artificial reefs with large surface area for new
colonies of sessile invertebrates to establish (Wolfson et al. 1979). In addition, bringing
new colonies of sessile invertebrates could also alter the ecological niches and change
food web dynamics (Langhamer et al. 2009).
Although the preferred wave energy installation sites are in low-relief fine
sediment habitats, it is thought that as the currents flow around the platforms, greater
volumes of sediments will be sent to water columns, possibly exposing nearby rocky
habitats to increasing sedimentation. Increasing sedimentation in some coral reefs have
shown to exert negative effects through smothering the colonies, such as reduced
48
recruitment, decreased net productivity, and decreased calcification (Rogers 1990). The
stations in both Delta and ROV Hammerhead surveys showed that the continental shelf
off Washington and Oregon has habitats with a wide diversity of physical features
ranging from low-relief mud and gravel to high-relief rocky habitats and rocky habitats
covered with fine sediment. Based on the past studies and speculations of what direct and
indirect effects the wave energy installations would have on macroinvertebrate
communities, it can be hypothesized that in the Pacific Northwest, the fine sediment
habitats occupied by sea pen colonies and few other motile invertebrates (sand star and
crustaceans) could face the greater change as the installations may bring new colonies of
sessile invertebrates to settle in these artificial reefs. Along with these invertebrates, other
species with adaptations to both hard-surface and fine sediment surfaces could arrive,
potentially competing with locally native invertebrates such as sand stars and sea pens for
food and other resources. If the rate of sedimentation on nearby reef increases due to
offshore installation, this could pose a threat to nearby reefs composed of sponges,
gorgonians, and crinoids, as their colonies could be smothered by increased
sedimentation rates; these sessile invertebrates may be forced to adapt different survival
strategies to maintain their viability in conditions with rapid sedimentation. With the
increasing mortality of sponges and gorgonians, the overall community diversity in terms
of macroinvertebrate numbers and taxa would also decline, whereas the diversity in finesediment regions where installations are established could experience greater invertebrate
diversity through increased ecological niche availability.
49
CONCLUSION
Of substratum types, two major substratum groups appear to be reliable indicators
in determining different macroinvertebrate assemblages: moderate to high relief rocky
habitats composed primarily of flat and ridge rocks, and low-relief fine sediment habitats
composed primarily of small-size grain substrata including mud, pebble, gravel, and
cobbles. While the majority of macroinvertebrate taxa, including both sessile and motile,
often were associated with high-relief group, these taxa can also be differentiated across
different kinds of steepness. The low-relief fine sediment group was most often
associated with motile invertebrates, but through this study, it appeared that finesediment substrata composed mainly of mud, boulders, and gravel can yield unique
invertebrate associations. As suggested by the taxon-substrata associations, the MM and
RM, or high-relief rock with fine sedimentation, were more highly correlated with
macroinvertebrate community patterns than other substrata types. Latitude was also
shown as a reliable variable, indicating a possibility of existing latitudinal gradients of
macroinvertebrate communities along the continental shelf. Although it is difficult to
accurately speculate how the macroinvertebrate communities in the continental shelf off
Oregon and Washington will be impacted by potential anthropogenic disturbances
without selectively choosing stations based on before and after impacts, results of this
study can be useful in predicting the community compositions of other unsampled
regions, based on their topographic features. The Delta stations were collected in early to
mid-1990s before important management changes (Strom 2006) while the ROV
Hammerhead stations were collected after these changes, and provide the most up-to-date
50
view of macroinvertebrate communities in Washington and Oregon’s continental shelf.
Studies of macroinvertebrate communities from both Delta and ROV Hammerhead
datasets can be important in reducing the uncertainties of these relatively unknown
communities but also can be used to structure baseline data for future regulations and
decisions on limiting trawling activities and the long-term impacts of potential offshore
wave energy installations.
51
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Tissot, B.N. 2008. Invertebrates of the Pacific Continental Shelf. Vancouver, WA:
Washington State University, Vancouver.
Tissot, B.N., M.A. Hixon, and D.L. Stein. 2007. “Habitat-based Submersible Assessment
of Macro-invertebrate and Groundfish Assemblages at Heceta Bank, Oregon,
from 1988 to 1990.” Journal of Experimental Marine Biology and Ecology 352
(1): 50–64.
Tissot, B.N., M.M. Yoklavich, M.S. Love, K. York, and M. Amend. 2006. “Benthic
Invertebrates That Form Habitat on Deep Banks Off Southern California, with
Special Reference to Deep Sea Coral.” Fisheries Bulletin 104: 167–181.
Watling, L., and E.A. Norse. 1998. “Disturbance of the Seabed by Mobile Fishing Gear:
a Comparison to Forest Clearcutting.” Conservation Biology 12 (6): 1180–1197.
Weston, D.P. 1988. “Macrobenthos-sediment Relationships on the Continental Shelf Off
Cape Hatteras, North Carolina.” Continental Shelf Research 8 (3): 267–286.
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Offshore Oil Platform.” Marine Ecology Progress Series 1: 81–89.
59
CHAPTER I FIGURES & TABLES
Figure 1 Distribution of Delta (n = 21) and ROV Hammerhead (n = 24) stations in Pacific Northwest’s
continental shelf
Coquille Bank
1993
(n = 8)
Siltcoos Reef
1995 (n=7);
2011 (n=10)
Grays Bank Shallow
1994 (n = 2)
Grays Bank
2011 (n = 14)
Grays Bank Deep
1994 (n=4)
60
Figure 2 Distribution of ROV Hammerhead’s Gray Bank stations (n = 14), with tracklines (blue) overlaid
across planned lines (yellow)
Grays Bank 2011
61
Figure 3 Distribution of ROV Hammerhead’s Siltcoos Reef stations (n = 10), with tracklines (red) overlaid
across planned lines (yellow)
Siltcoos Reef 2011
62
Figure 4 Taxon-substratum associations of Grays Bank 1994 stations surveyed by Delta in Correspondence
Analysis ordination. Invertebrate densities were square-root transformed to alleviate density differences
between substrata types. Blue circles and red triangles indicate taxa and substrata type, respectively.
63
Figure 5 Taxon-substratum associations of Siltcoos Reef 1995 stations surveyed by Delta in Correspondence
Analysis ordination. Invertebrate densities were square-root transformed to alleviate density differences
between substrata types. Blue circles and red triangles indicate taxa and substrata type, respectively.
64
Figure 6 Taxon-substratum associations of Coquille Bank 1993 stations surveyed by Delta in Correspondence
Analysis ordination. Invertebrate densities were square-root transformed to alleviate density differences
between substrata types. Blue circles and red triangles indicate taxa and substrata type, respectively.
65
Figure 7 Taxon-substratum associations of Grays Bank 2011 stations surveyed by ROV Hammerhead in
Correspondence Analysis ordination. Invertebrate densities were square-root transformed to alleviate density
differences between substrata types. Blue circles and red triangles indicate taxa and substrata type,
respectively.
66
Figure 8 Taxon-substratum associations of Siltcoos Reef 2011 stations surveyed by ROV Hammerhead in
Correspondence Analysis ordination. Invertebrate densities were square-root transformed to alleviate density
differences between substrata types. Blue circles and red triangles indicate taxa and substrata type,
respectively.
67
Figure 9 Distribution of Delta stations based on taxa composition similarities and dissimilarities on the 2dimensional nMDS ordination plane. Stations were superimposed with significantly different assemblages
identified by SIMPROF. The invertebrate densities were square-root transformed and adjusted to the BrayCurtis similarity measure (GB = Grays Bank, SR = Siltcoos Reef, CB = Coquille Bank).
68
Figure 10 Distribution of ROV Hammerhead stations based on taxa composition similarities and
dissimilarities on the 2-dimensional nMDS ordination plane. Stations were superimposed with significantly
different assemblages identified by SIMPROF. The invertebrate densities were square-root transformed and
adjusted to the Bray-Curtis similarity measure (GB = Grays Bank, SR = Siltcoos Reef)
69
70
Table 1 List of taxa with highest contribution % in defining different macroinvertebrate
assemblages across the Delta stations. Results were based on the SIMPER 90%-cutoff
results. The assemblages C and E were excluded from this analysis because they each had
only one station. (GB = Grays Bank, SR = Siltcoos Reef, CB = Coquille Bank)
Assemblage
Stations
A
GB 3417, 3419
B
CB 3060-3062,
3067-3071
D
SR 3669, 36713674
F
SR 3668, 3670
G
GB 3416, 34203421
Avg.
Top Contributors
Similarity
Florometra serratissima
Shelf Sponge
Unidentified Sponge
Foliose Sponge
Pandalus platyceros
71.16
Allocentrotus fragilis
Mediaster aequalis
Branching Sponge
Parastichopus leukothele
Poraniopsis inflata
Branching Sponge
Florometra serratissima
Mediaster aequalis
70.41
Branching Red Gorgonian
Parastichopus californicus
Gorgonocephalus eucnemis
Henricia sp.
Parastichopus californicus
Branching Red Gorgonian
Laqueus californicus
Parastichopus leukothele
Shelf Sponge
Branching Sponge
Foliose Sponge
65.5
Mediaster aequalis
Henricia sp.
Subselliflorae
Pteraster tesselatus
Burrowing Anemone
Single Stalk Red Gorgonian
Spheciospongia confoederata
Subselliflorae
85.81
Luidia foliolata
Gorgonocephalus eucnemis
Single Stalk White Gorgonian
Subselliflorae
Branching White Gorgonian
47.2
Luidia foliolata
Unidentified Sponge
Mediaster aequalis
Allocentrotus fragilis
Contribution Cumulative
%
%
23.62
23.62
21.29
44.91
16.49
61.40
8.61
70.01
4.95
74.96
3.99
78.95
3.21
82.16
3.10
85.26
2.98
88.24
2.27
90.51
38.70
38.70
24.48
63.18
7.74
70.92
6.56
77.48
6.06
83.54
4.78
88.32
2.57
90.89
14.05
14.05
13.69
27.74
11.89
39.63
10.44
50.07
8.91
58.98
5.78
64.76
4.74
69.50
4.23
73.73
4.17
77.90
4.00
81.90
2.57
84.47
2.14
86.61
2.11
88.72
2.00
90.72
69.61
69.61
12.71
82.32
11.69
94.01
50.12
50.12
13.39
63.51
8.44
71.95
7.19
79.14
4.68
83.82
3.81
87.63
3.34
90.97
A
Species
Br Sponge
F. serratissima
Sh Sponge
Un Sponge
BR Gorgonian
Dissimilarity %
Sh Sponge
F. serratissima
BR Gorgonian
Un Sponge
SSR Gorgonian
Dissimilarity %
F. serratissima
L. californicus
Un Sponge
Sh Sponge
BR Gorgonian
Dissimilarity %
F. serratissima
Sh Sponge
Un Sponge
Fo Sponge
Bu Anemone
Dissimilarity %
F. serratissima
Subselliflorae
Sh Sponge
Un Sponge
Fo Sponge
Dissimilarity %
F. serratissima
Sh Sponge
SSW Gorgonian
Un Sponge
Subselliflorae
Dissimilarity %
C
D
E
F
G
B
Assemblage
16.87
12.54
9.46
9.03
5.51
83.4
16.5
14.47
11.98
10.41
4.86
98.81
20.54
14.88
12.95
6.04
4.6
96.5
14.67
12.02
9.61
7.43
7.04
69.38
13.13
12.19
11.93
9.53
6.92
74.5
C%
26.83
9.73
8.59
6.95
5.54
71.78
B
Br Sponge
F. serratissima
SSW Gorgonian
BR Gorgonian
P. californicus
Dissimilarity %
Br Sponge
F. serratissima
Subselliflorae
BR Gorgonian
M. aequalis
Dissimilarity %
Br Sponge
F. serratissima
BR Gorgonian
M. aequalis
P. californicus
Dissimilarity %
Br Sponge
F. serratissima
L. californicus
G. eucnemis
M. aequalis
Dissimilarity %
Br Sponge
F. serratissima
M. aequalis
P. californicus
G. eucnemis
Dissimilarity %
Species
29.83
20.6
7.58
4.95
4.54
88.08
30.86
21.62
10.8
5.93
5.59
93.31
34.02
23.87
6.52
6.16
5.16
97.16
29.79
21.05
9.8
4.56
3.9
68.23
35.85
21.34
5.99
5.05
4.81
66.18
C%
C
SSW Gorgonian
BR Gorgonian
SSR Gorgonian
F. serratissima
Subselliflorae
Dissimilarity %
Subselliflorae
BR Gorgonian
SSR Gorgonian
F. serratissima
P. californicus
Dissimilarity %
BR Gorgonian
SSR Gorgonian
F. serratissima
P. leukothele
Branching Sponge
Dissimilarity %
L. californicus
P. californicus
SSR Gorgonian
Sh Sponge
BR Gorgonian
Dissimilarity %
Species
17.03
16.54
9.79
8.39
6.6
74.02
22.22
18.46
10.7
9.08
5.6
88.14
24.83
14.4
12.22
7.53
4.55
89.08
19.31
9.54
8.61
7.48
6.39
55.97
C%
D
L. californicus
SSW Gorgonian
P. californicus
BR Gorgonian
P. leukothele
Dissimilarity %
Subselliflorae
L. californicus
BR Gorgonian
P. californicus
P. leukothele
Dissimilarity %
L. californicus
BR Gorgonian
P. californicus
P. leukothele
Sh Sponge
Dissimilarity %
Species
14.31
12.24
8
7.25
5.63
81.07
14.95
14.83
8.95
8.38
6.58
89.24
16.97
10.45
9.79
7.75
6.79
96.24
C%
E
SSW Gorgonian
Subselliflorae
BW Gorgonian
M. farcimen
Un Sponge
Dissimilarity %
Subselliflorae
G. eucnemis
L. foliolata
O. rubsecens
M. farcimen
Dissimilarity %
Species
27.82
14.82
6.85
5.71
4.83
87.79
66.57
11.72
5.47
2.99
2.44
77.88
C%
F
SSW Gorgonian
Subselliflorae
BW Gorgonian
M. farcimen
G. eucnemis
Dissimilarity %
Species
23.38
21.18
5.78
5.18
5.15
73.27
C%
Table 2 Dissimilarity % and the contribution (C%) of five most important taxa to the dissimilarity between
any combinations of assemblages in the Delta stations. Results were based on SIMPER’s 90%-cutoff
(Anemone, gorgonian, and sponge abbreviations: Br = branching, Bu = burrowing, BR = branching red, BW =
branching white, Fo = foliose, Sh = shelf, SSR = single stalk red, SSW = single stalk white, Un =
unidentified). For the complete genus names, refer to Table 1.
71
72
Table 3 List of taxa with highest contribution % in defining different macroinvertebrate
assemblages across the ROV Hammerhead stations. Results were based on the
SIMPER’s 90%-cutoff results. The assemblages A and B were excluded from this
analysis since they each had only one station.
Assemblage
C
Stations
SR 2-4, 68, 11
Avg.
Similarity
73.17
Top Contributors
Shelf sponge
Branching Red Gorgonian
Parastichopus californicus
Branching Sponge
Single Stalk White Gorgonian
Branching White Gorgonian
Mediaster aequalis
Metridium farcimen
Pandalus sp.
Parastichopus leukothele
Single Stalk Red Gorgonian
Henricia sp.
Gorgonocephalus eucnemis
Stylasterias forreri
Ophiacantha sp.
D
E
GB 5, 7
GB 16-18
74.09
78.13
Subselliflorae
Branching Red Gorgonian
Branching White Gorgonian
Single Stalk Red Gorgonian
Single Stalk White Gorgonian
Metridium farcimen
Shelf Sponge
Branching Sponge
Luidia foliolata
Parastichopus californicus
Semisuberites cribrosa
Stomphia coccinea
Henricia sp.
Branching Red Gorgonian
Branching Sponge
Metridium farcimen
Shelf Sponge
Single Stalk Red Gorgonian
Parastichopus californicus
Henricia sp.
Urticina columbiana
Mycale sp.
Single Stalk White Gorgonian
Stylasterias forreri
Semisuberites cribrosa
Contribution Cumulative
%
%
15.25
15.25
11.53
26.78
8.44
35.22
7.94
43.16
7.85
51.01
7.05
58.06
6.62
64.68
6.33
71.01
3.99
75.00
3.07
78.07
3.06
81.13
2.88
84.01
2.74
86.75
2.14
88.89
1.57
90.46
28.46
28.46
11.96
40.42
10.02
50.44
7.99
58.43
6.05
64.48
5.60
70.08
4.89
74.97
3.61
78.58
3.44
82.02
2.66
84.68
2.43
87.11
2.17
89.28
1.73
91.01
12.99
12.99
12.27
25.26
10.53
35.79
10.45
46.24
6.19
52.43
5.82
58.25
5.72
63.97
5.37
69.34
4.28
73.62
4.16
77.78
2.50
80.28
2.48
82.76
73
Table 3 (Continued)
Assemblage
Stations
Avg.
Similarity
E
GB 16-18
78.13
F
GB 8, 1013, 15
74.81
Top Contributors
Ascidia paratropa
Pteraster tesselatus
Branching White Gorgonian
Piaster brevispinus
Branching Red Gorgonian
Single Stalk Red Gorgonian
Branching Sponge
Shelf Sponge
Single Stalk White Gorgonian
Branching White Gorgonian
Parastichopus californicus
Semisuberites cribrosa
Metridium farcimen
Henricia sp.
Urticina columbiana
Mycale sp.
G
GB 3, 9,
14, SR 9
37.86
Stylasterias forreri
Pteraster tesselatus
Stomphia coccinea
Ascidia paratropa
Subselliflorae
Luidia foliolata
Stomphia coccinea
Branching White Gorgonian
Urticina columbiana
Single Stalk White Gorgonian
Urticina coriacea
Contribution Cumulative
%
%
2.42
85.18
2.38
87.56
1.90
89.46
1.76
91.22
18.37
18.37
12.12
30.49
9.63
40.12
8.12
48.24
7.25
55.49
6.43
61.92
4.26
66.18
4.06
70.24
4.05
74.29
3.68
77.97
3.32
81.29
2.48
83.77
2.26
86.03
1.57
87.60
1.45
89.05
1.37
90.42
45.01
45.01
14.83
59.84
9.19
69.03
5.97
75.00
5.18
80.18
5.09
85.27
4.76
90.03
A
Species
Pandalus sp.
M. farcimen
BR Gorgonian
M. quadrispina
BW Gorgonian
Dissimilarity %
Pandalus sp.
M. farcimen
Sh Sponge
BR Gorgonian
P. chitinoides
Dissimilarity %
Pandalus sp.
M. farcimen
Subselliflorae
BR Gorgonian
P. californicus
Dissimilarity %
Pandalus sp.
M. farcimen
Br Sponge
SSW Gorgonian
Mycale sp.
Dissimilarity %
Pandalus sp.
M. farcimen
SSR Gorgonian
Bu Anemone
S. cribrosa
Dissimilarity %
Pandalus sp.
M. farcimen
BR Gorgonian
P. californicus
SSW Gorgonian
Dissimilarity %
C
D
E
F
G
B
Assemblage
29.18
13.73
9.54
4.48
4.41
79.46
35.18
13.46
4.89
3.39
2.93
51.12
31.97
7.84
5.24
3.25
3.25
54.75
34.1
13.07
10.81
3.42
3.3
57.25
35.26
13.16
7.8
4.45
2.66
42.22
C%
31.67
14.71
10.63
4.77
4.4
44.71
B
SSW Gorgonian
Pandalus sp.
BW Gorgonian
Sh Sponge
Subselliflorae
Dissimilarity %
BR Gorgonian
Pandalus sp.
SSR Gorgonian
Br Sponge
M. quadrispina
Dissimilarity %
Pandalus sp.
BR Gorgonian
Br Sponge
BW Gorgonian
SSW Gorgonian
Dissimilarity %
Subselliflorae
Pandalus sp.
BR Gorgonian
SSW Gorgonian
M. quadrispina
Dissimilarity %
BR Gorgonian
Sh Sponge
Pandalus sp.
Br Sponge
P. californicus
Dissimilarity %
Species
11.87
11.04
10.84
6.82
6.57
71.32
13.47
12.07
9.55
6.3
5.23
52.8
9.57
8.68
8.51
7.12
6.48
64.24
17.44
13.73
7.86
7.27
5.95
52.05
11.8
11.16
7.66
6.23
6.18
39.32
C%
C
Sh Sponge
BR Gorgonian
P. californicus
Subselliflorae
Br Sponge
Dissimilarity %
Sh Sponge
SSR Gorgonian
Pandalus sp.
BR Gorgonian
M. aequalis
Dissimilarity %
Pandalus sp.
Br Sponge
BR Gorgonian
BW Gorgonian
U. columbiana
Dissimilarity %
Subselliflorae
Sh Sponge
Pandalus sp.
P. californicus
M. aequalis
Dissimilarity %
Species
12.56
10.33
6.84
6.34
5.74
80.6
8.65
8.06
7.3
7.24
4.93
42.53
6.68
5.96
5.7
5.42
4.95
45.05
16.65
10.74
6.37
5.46
5.38
53.6
C%
D
Subselliflorae
BR Gorgonian
BW Gorgonian
SSR Gorgonian
SSW Gorgonian
Dissimilarity %
Subselliflorae
BR Gorgonian
Br Sponge
SSR Gorgonian
BW Gorgonian
Dissimilarity %
Subselliflorae
Br Sponge
Sh Sponge
M. farcimen
BW Gorgonian
Dissimilarity %
Species
14.13
13.76
8.87
8.03
5.84
61.65
22.8
8.78
8.21
5.62
4.4
41.88
18.69
10.62
6.76
6.34
5.93
53.03
C%
E
BR Gorgonian
Br Sponge
Sh Sponge
M. farcimen
Subselliflorae
Dissimilarity %
M. farcimen
BW Gorgonian
Br Sponge
BR Gorgonian
SSR Gorgonian
Dissimilarity %
Species
11.37
10.3
8.52
7.72
7.5
84.99
9.82
7.94
7.46
7.4
6.48
30.81
C%
F
BR Gorgonian
SSR Gorgonian
Br Sponge
Subselliflorae
Sh Sponge
Dissimilarity %
Species
15.4
9.44
7.62
7.27
6.33
78.42
C%
Table 4 Dissimilarity % and the contribution (C%) of five most important taxa to the dissimilarity between
any combinations of assemblages in the ROV Hammerhead stations. Results were based on SIMPER’s 90%cutoff results. For the anemone, gorgonian, and sponge abbreviations, refer to Table 4. For the complete genus
names, refer to Table 1.
74
G
F
E
D
C
B
A
20%
40%
60%
80%
100%
Figure 11 Proportions of different substrata across Delta assemblages identified by SIMPROF. See Table 3
for details on each assemblage’s stations.
0%
BM
FB
FC
FF
FG
FM
FP
MB
MC
MM
MP
RB
RC
RG
RM
RP
RR
75
G
F
E
D
C
B
A
0%
40%
60%
80%
100%
Figure 12 Proportions of different substrata across ROV Hammerhead assemblages identified by SIMPROF.
See Table 6 for details on each assemblage’s stations.
20%
BB
BM
FB
FC
FF
FG
FM
FP
GG
GM
MB
MC
MG
MM
MP
PM
RB
RC
RG
RM
RP
RR
76
77
Table 5 Top ten sets of environmental variables that are most highly correlated with the
invertebrate structure in the Delta and ROV Hammerhead stations based on the BIOENV results. All taxa densities were square-root transformed, and all the environmental
data were normalized (after substrata percentages were log-transformed).
Dataset
Delta
ROV Hammerhead
Environmental Variables
MM
MM, Latitude
MM, RM, Latitude
MM, RM, Depth
BM, MM, Latitude
MM, RM, Temp
BM, MM, RM, Latitude
MM, RM, Depth, Latitude
BM, MM, RM, Depth
MM, MP
GG, RM, Temp
GG, RM, Latitude
GG, RM, RR, Temp
GG, RM, RR, Latitude
RM, Temp
GG, RM, RR, Depth
RM, Latitude
MG, MM, RM, RR, Temp
GG, MM, RM, RR, Temp
GG, MM, RM, RR, Latitude
Correlation Coefficient
0.799
0.779
0.768
0.76
0.744
0.739
0.731
0.727
0.726
0.726
0.789
0.788
0.784
0.781
0.777
0.777
0.774
0.767
0.764
0.763
78
APPENDICES
79
Appendix A Table 1 Total raw count of macroinvertebrate taxa across all five sites in
the Delta and ROV stations. Includes total counted (n = 169,856), and each taxon’s %
contribution to the total count (GB = Grays Bank, SR = Siltcoos Reef, CB = Coquille
Bank). Note that GB Deep and Shallow were represented separately.
Phyla
Taxon
GB
Deep
1994
PORIFERA
Anthomastus ritteri
Barrel Sponge
Branching Sponge
Foliose Sponge
Halichondria panicea
Mycale sp.
Orange Encrusting Sponge
Phakellia sp.
Polymastia pacifica
Semisuberites cribrosa
Shelf Sponge
Spheciospongia confoederata
Unidentified Sponge
Upright Flat Sponge
6
72
225
1
4
1369
14
1084
22
CNIDARIA
Branching Purple Gorgonian
Branching Red Gorgonian
Branching White Gorgonian
Burrowing Anemone
Cribrinopsis fernaldi
Dromalia alexandri
Metridium farcimen
Ptilosarcus gurneyi
Single Stalk Purple Gorgonian
Single Stalk Red Gorgonian
Single Stalk White Gorgonian
Stomphia coccinea
Stylaster californicus
Subselliflorae
Urticina columbiana
Urticina coriacea
Urticina piscivora
1
110
324
866
15
425
1
12
ECHINODERMATA Allocentrotus fragilis
Ceramaster patagonicus
Crossaster papposus
Dermasterias imbricata
Florometra serratissima
Gorgonocephalus eucnemis
Henricia sp.
Hippasteria spinosa
Luidia foliolata
Mediaster aequalis
Ophiacantha sp.
Ophiopsilla californica
Orthasterias koehleri
Parastichopus californicus
Parastichopus leukothele
Pisaster brevispinus
Poraniopsis inflata
145
2561
3
18
2
18
113
7
5
10
89
25
GB
GB
SR
SR
CB
Total # % of
Shallow 2011 1995 2011 1993 of indiv. total
1994
1
1
0.00
4
10
0.01
- 3158
273 1008 52513
57024 33.57
45
234
29
50
583
0.34
1
0.00
430
430
0.25
4
3
11
0.01
22
22
0.01
6
6
12
0.01
338
1
339
0.20
- 2021
624 4085
8099
4.77
51
65
0.04
1
32
23
1140
0.67
10
3
35
0.02
Total no. of Poriferan individuals 67772 39.90
Total no. of taxa
14
7
51 6794 1378 3698 2635
5 1161
- 1303
14
4
138
145
12
10
2
251 1627
27 1740 3252
66
9
1
15 2090
31
214
268
947 1148
2 1765
2
679
18
95
72
1
29 2385 1684
146
26
5
554
9
3
88
2
2
1
2
18
1
Total no. of Cnidarian individuals
Total no. of taxa
1
61
-
4
5
2
35
589
88
91
318
9
775
2
71
-
3
6
252
56
125
3
125
185
6
11
1128
647
13
3
37
1
37
21
1
14 35158
187 1429
170
263
7
5
23
80
705 1726
61
17
149
1251 1398
300
198
2
17
7
0.00
14557
8.57
2593
1.53
623
0.37
10
0.01
2
0.00
6897
4.06
75
0.04
1
0.00
2618
1.54
4728
2.78
881
0.52
1
0.00
4695
2.76
571
0.34
93
0.05
34
0.02
38386 22.60
17
190
4
69
3
37985
1710
1165
17
395
2820
392
5
196
4552
1236
71
57
0.11
0.00
0.04
0.00
22.36
1.01
0.69
0.01
0.23
1.66
0.23
0.00
0.12
2.68
0.73
0.04
0.03
80
Appendix A (Continued)
Phyla
Taxon
ECHINODERMATA Poraniopsis jordani
Psolus chitonoides
Psolus squamatus
Pteraster militaris
Pteraster tesselatus
Pycnopodia sp.
Solaster dawsoni
Solaster endeca
Solaster paxillatus
Solaster sp.
Stylasterias forreri
GB
Deep
1994
5
135
22
1
19
GB
GB
SR
SR
CB
Total # % of
Shallow 2011 1995 2011 1993 of indiv. total
1994
4
9
0.01
35
8
27
70
0.04
135
0.08
3
3
0.00
123
40
7
3
173
0.10
8
43
15
7
95
0.06
24
2
26
0.02
4
4
0.00
4
4
0.00
1
2
1
14
19
0.01
134
12
88
13
266
0.16
Total no. of Echinoderm 51671 30.42
Total no. of taxa
28
CHORDATA
Ascidia paratropa
1
121
1
3
4
Total no. of Chordate individuals
Total no. of taxa
130
130
1
0.08
0.08
MOLLUSCA
Dirona albolineata
Laqueus californicus
Octopus dofleini
Octopus rubescens
Mud Scallop
Tochuina tetraquetra
Tritonia diomedea
Unidentified Snail
1
3
1
- 6544
5
16
5
3
4
9
1
4
7
3
1
Total no. of Mollusc individuals
Total no. of taxa
1
6544
5
24
13
13
3
4
6607
8
0.00
3.85
0.00
0.01
0.01
0.01
0.00
0.00
3.89
NEMERTEA
Cerebratulus californiensis
Tubulanus polymorphus
-
1
3
Total no. of Nemertean individuals
Total no. of taxa
1
3
4
2
0.00
0.00
0.00
ARTHROPODA
Cancer sp.
Hermit Crab
Lopholithodes foraminatus
Munida quadrispina
Pandalus platyceros
Pandalus sp.
2
28
110
-
7
14
5
9
1
41
8
1
12
1
1
210
- 4836
Total no. of Arthropod individuals
Total no. of taxa
35
52
42
211
110
4836
5286
6
0.02
0.03
0.02
0.12
0.06
2.85
3.11
GRAND TOTAL NO. OF INDIVIDUALS 169856
76
GRAND TOTAL NO. OF TAXA
100
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Figure 1 Substrata % proportions across five sites. Abbrev: GB = Grays Bank, SR = Siltcoos Reef, CB =
Coquille Bank. Note that GB Deep and Shallow were represented separately.
CB 1993
SR 2011
SR 1995
GB 2011
GB Shallow 1994
GB Deep 1994
BB
BM
CM
FB
FC
FF
FG
FM
FP
GG
GM
MB
MC
MG
MM
MP
PM
RB
RC
RG
RM
RP
RR
81
Appendix B
82
Appendix C Table 1 The mean depth (meters) of all stations (n = 45) across the Delta
and ROV Hammerhead sites (GB = Grays Bank, SR = Siltcoos Reef, CB = Coquille
Bank).
Delta
Site
Station Mean Depth
GB Deep 1994
3417
191.72
3419
204.01
3420
167.12
3421
167.33
GB Shallow 1994
3415
54.49
3416
67.10
SR 1995
3668
108.71
3669
109.11
3670
119.90
3671
109.32
3672
114.00
3673
112.08
3674
109.24
CB 1993
3060
98.20
3061
85.19
3062
88.13
3067
94.51
3068
90.19
3069
93.24
3070
97.83
3071
125.62
ROV Hammerhead
Site
Station Mean Depth
GB 2011
3
72.82
5
75.24
7
79.31
8
75.15
9
69.18
10
78.94
11
66.07
12
62.96
13
77.33
14
76.29
15
64.83
16
57.88
17
55.84
18
56.84
SR 2011
1
113.14
2
111.36
3
116.34
4
105.91
6
105.06
7
103.70
8
104.18
9
110.47
11
103.00
12
104.12
83
CHAPTER II: Investigation of Key Asteroid Echinoderms in Benthic
Macroinvertebrate Assemblages
84
INTRODUCTION
Asteroid Echinoderms, or sea stars, are one of the most familiar benthic motile
macroinvertebrates. Sea stars have a wide array of morphology, function, life history, and
dietary characteristics (Paine 1966; Dayton 1971; Dayton et al. 1974). In some intertidal
communities, sea stars are one of the most abundant benthic predators (Jalbert et al. 1989;
Himmelman 1991). Studies of sea stars have demonstrated their influential roles in
community ecology; one of the most widely known role is the “Keystone Species” of
Pisaster ochraceus (Paine 1966). In terms of dietary habits, some species are specialists,
such as Solaster dawsonii, which prey on other sea stars, and Solaster stimpsonii, which
feed primarily on Holothurians (Mauzey et al. 1968). Others are generalists, such as
Pycnopodia sp., Mediaster aequalis, and Pteraster tesselatus (Menge 1972; Mauzey et al.
1968). Currently in the Pacific Northwest, very few studies are available about sea star
ecology and distributions away from intertidal habitats. Most of these studies take place
in Puget Sound. Mauzey et al. (1968) provided a study of observed behavioral traits such
as feeding habits of each sea star that is commonly found in Puget Sound, while
Birkeland (1974) provided a study of orange sea pen Ptilosarcus gurneyi and seven of its
predators in Puget Sound, five of which were sea stars. Both Mauzey et al. (1968) and
Birkeland (1974) have found that sea stars greatly vary between species in terms of
capturing prey. Furthermore, of the sea stars that were observed, many were known to
change their diet by seasons, while species that were widespread across diverse range of
habitats were known to feed on different prey item per habitat.
85
In an attempt to reduce uncertainties of the role of sea stars in Pacific Northwest
continental shelf waters, my goal is to determine if particular sea star species exert
influence on the benthic macroinvertebrate assemblage patterns in Pacific Northwest
continental shelf waters. Thus I addressed the following objectives:
i.
Determine if there are sea star species that are potential candidates of being
descriptive in describing macroinvertebrate assemblage patterns
ii.
Determine if these sea star species are indeed descriptive species, after taking
account of all the other available environmental variables
iii.
Investigate species-specific associations based on life history and behavior
To address these objectives, I used the sea stars were found to be significant contributors
to macroinvertebrate assemblages in both Delta and ROV Hammerhead datasets from
Chapter 1. To address the third objective, specifically, I have made the following
hypotheses for sea stars that appear in more than one assemblage across both Delta and
ROV Hammerhead datasets in Chapter 1. These hypotheses are the following:
Henricia spp: Although little knowledge exists about the ecology and life history
of species in this genus, based on past laboratory observations of Henricia leviscula and
Henricia sanguinolenta morphology, the blood star, Henricia, appears to primarily feed
on sponges (Mauzey et al. 1968, Lambert 2000). Some Henricia species have been found
with remains of small sponge colonies in their stomach folds, thus indicating that they
may contribute tissue damage and potential mortality to sponge colonies (Mauzey et al.
1968). Furthermore, the damage on sponge tissues inflicted by Henricia spp. could make
these damaged sponges susceptible to further tissue damage and increased likelihood of
86
breakage in turbulent currents and high-wave action caused by storms (Sheild and
Witman 1993). Therefore, I hypothesized that the densities of Henricia spp. would be
inversely correlated with the densities of Branching Sponges, since the branching
morphology of these sponges could make them more vulnerable to breakage and other
damages caused by strong currents after their tissues have already been damaged by
Henricia spp.
Luidia foliolata: The sand star, Luidia foliolata, is a species that primarily inhabits
soft substrates (Lambert 2000). It is known for the five long arms and dull grey or brown
coloration that often blends well with the surrounding environment (Lambert 2000). It is
also known for its behavior of burying in soft substrates; although the mechanisms for
burrowing are not well known, it is known that this species' tube feet are long and
versatile enough to disturb the silty substrate (Mauzey et al. 1968). The soft substrate
habitats along west coast of the North America often are occupied by colonies of white
sea pens belonging to the suborder Subselliflorae (Strom 2006). Sea pens are often
susceptible to damage caused by physical disturbances of habitats since the axial rod of
sea pens are usually brittle (Greathead et al. 2007). Since one of L. foliolata's traits is its
burrowing ability, I hypothesized that greater densities of these sea stars would reduce
white Subselliflorae sea pen colonization, since the burrowing behavior could be
responsible for substrate disturbance that causes sea pens' inability to secure in sediment.
Thus I hypothesized that the densities of L. foliolata would be inversely correlated with
the densities of Subselliflorae sea pens.
87
Mediaster aequalis: The vermillion red star, Mediaster aequalis, has one of the
most opportunistic diets of any sea stars; its diet consists of sea pens, sponges, algal
materials, and detritus (Birkeland 1974, Mauzey et al. 1968). In some places, such as the
Gabriola Passage in British Columbia in December, about 56% of M. aequalis were
observed feeding on detritus (Lambert 2000). It is also a widespread species that inhabits
habitats of various grain sizes, ranging from high-relief rocks to pebbles (Lambert 2000).
Another common echinoderm present throughout the hard-substrate habitats of the
Pacific Northwest is the red sea cucumber, Parastichopus californicus (Lambert 1997). P.
californicus primarily feeds on organic matter and detritus as it roams across the seafloor
and inserts the organic matter with its tentacles (Lambert 1997). From past literature
about dietary preference similarity between the M. aequalis and P. californicus, it
appears that their prey resources overlap greatly, thus leading to the possibility of
resource competition between these two species. Thus, I hypothesized that the density of
M. aequalis across different stations would be inversely correlated with the density of P.
californicus.
Pteraster tesselatus: The cushion star, Pteraster tesselatus, is characterized by
short puffy arms, broad disc, and overall, a fat, rotund structure; it is particularly known
for its ability to excrete slime upon disturbance (Lambert 2000). A few studies in the past
have observed P. tesselatus consuming sponges that are small and encrusting in
morphology (Mauzey et al. 1968). This could be attributed to their morphology, since
their short puffy arms may limit their movement flexibility, thus preventing them from
successfully clambering and attacking sponges of branching morphology. With this in
88
mind, I hypothesized that there would be negative correlation between the densities of P.
tesselatus and the shelf sponge, since shelf sponges were distinguished from other
sponges based on their relatively flat surface as opposed to branching morphology that
other sponges had, thus making these sponges a possible favorable target for P. tesselatus.
Stylasterias forreri: Many studies in the past have indicated that sponge colonies
are subjected to fish predation (Ruzicka and Gleason 2008). Studies of temperate reefs
around the world have suggested possible changes in sponge diversity and richness
structure affected by spongivorous fish predation (Ruzicka and Gleason 2009). In some
cases, fish predation on sponges has shown to limit sponge growth forms over time,
which could potentially weaken their internal structures and increase their vulnerability to
other threats (Loh and Pawlik 2009). The velcro star, Stylasterias forreri, is a species that
inhabits hard substrata and reefs, and it usually feeds on bivalves, chitons, and sponges
(Lambert 2000). However, S. forreri is special in that it feeds on motile prey such as fish
by capturing them with pedicellariae (Robilliard 1971). The dorsal surface of S. forreri is
covered with thousands of crossed pedicellariae that immediately activates upon contact;
these pedicellariae are equipped with sharp hooks and act like pincers, grasping the
motile prey with vice-like grip (Chia and Amerongen 1974). The S. forreri is often wellblended against background, and some observations have recorded fish being captured as
it mistakes the dorsal surface of S. forreri as rocky substratum (Chia and Amerongen
1974). Therefore, I hypothesized that there would be a positive correlation between the
densities of S. forreri and the Shelf Sponge, since the increasing presence of S. forreri
would lead to increasing predation on spongivorous fish, thus indirectly protecting the
89
sponge colonies. I selected the Shelf Sponge since its relatively flat morphology in the
reefs would allow predatory fish to approach closer to the rocky substratum surface, thus
increasing the possibility of their contact with the S. forreri.
90
METHODS
BIO-ENV with Modified Matrix
The sea stars that appeared in the top 90% contributing list per station group
(SIMPER analysis) were removed from the biota matrix for each dataset and added to the
environmental matrix as possible explanatory variables. After moving the sea stars, the
Delta biota matrix had 54 species, and the environmental matrix had total of 26
environmental variables: 18 different substratum percentages, depth (meters),
temperature (Celsius), latitude, and the densities (#/m2) of five sea star species. After
moving the sea stars, the ROV biota matrix had 54 species, and the environmental matrix
had total of 32 environmental variables: 22 different substratum percentages, depth
(meters), temperature (Celsius), Salinity (PSU), latitude, and the densities (#/m2) of six
sea star species. To determine if sea stars are indeed descriptive species in describing
different assemblage patterns after accounting for all other available environmental
parameters, I ran a BIO-ENV procedure, available in PRIMER 6th Version (Plymouth
Routines in Multivariate Ecological Research) once each per dataset (Delta and ROV
Hammerhead). Before running the BIO-ENV, for each environmental matrix, the
substrata percentages were log (x+1) transformed, and the sea star densities were squareroot transformed before the entire environmental data was normalized.
Pearson’s Correlation Tests
After determining which sea stars were influential species in determining
invertebrate assemblage patterns after all the other environmental variables have been
91
accounted for based on the BIO-ENV results, I investigated whether there were potential
species-specific relationships between these sea stars and a selected invertebrate species
that possibly face direct or indirect effects based on the sea star’s dietary behavior and
life history using the limited information from past peer-reviewed literature. I tested each
hypothesis with the Pearson’s Correlation Test at p = 0.05 significance level. All
densities were square-root transformed before running the tests.
92
RESULTS
Descriptive Species in the Delta Stations
Five Asteroid Echinoderms were identified as descriptive candidates in
characterizing invertebrate communities of Delta stations, since they made part of the
90% contribution in distinguishing assemblages. These five species were the blood star,
Henricia spp., sand star, Luidia foliolata, vermillion red star, Mediaster aequalis, thorny
star, Poraniopsis inflata, and slime star, Pteraster tesselatus (Table 6).
When the five Asteroid Echinoderms were added to the environmental matrix, the
result of best environmental variable subsets that explain the invertebrate community
(minus five Asteroid Echinoderms) was different from the environmental subsets
obtained without accounting for Asteroid Echinoderms in the environmental matrix
(Table 7). The variable combination that exhibited the highest correlation with squareroot transformed minus Asteroid Echinoderm invertebrate community structure were
boulder-mud (BM), mud-mud (MM), ridge-mud (RM), depth, latitude, L. foliolata, M.
aequalis, Henricia spp., and P. tesselatus (r = 0.792). The correlation dropped slightly
when the P. tesselatus was removed from the variable combination (r = 0.789). Thus,
after the environmental variables BM, MM, RM, depth, and latitude were taken into
account, L. foliolata, M. aequalis, Henricia spp., and P. tesselatus were the Asteroid
Echinoderm species whose densities were correlated with the overall structure of the
benthic macroinvertebrate communities in stations surveyed by Delta.
93
Descriptive Species in the ROV Hammerhead Stations
Six Asteroid Echinoderms were identified as descriptive candidates in
characterizing invertebrate communities of ROV Hammerhead stations, since they made
part of the 90% contribution in distinguishing assemblages. These six species were
Henricia spp., L. foliolata, M. aequalis, giant pink star, Pisaster brevispinus, P. tesselatus,
and the velcro star, Stylasterias forreri (Table 6).
When the six Asteroid Echinoderms were added to the environmental matrix, the
correlation between the variable subsets and the invertebrate community structure (minus
the six Asteroid Echinoderms) was highest when the environmental variable subset was
composed of GG, RM, latitude, L. foliolata, and S. forreri (r = 0.855) (Table 7). Thus,
after the variables GG, RM, and latitude were taken into account, L. foliolata and S.
forreri were the Asteroid Echinoderm species whose densities were correlated with the
overall macroinvertebrate community structure in the stations surveyed by ROV
Hammerhead.
Specific Relationships with Asteroid Echinoderms
Based on the past literature about the life history and feeding traits, I proposed the
following hypotheses about the sea stars that were considered influential drivers of
invertebrate community structure patterns. Briefly, they were the following:
i.
Henricia sp. densities will be negatively correlated with the densities of
Branching Sponge.
94
ii.
L. foliolata densities will be negatively correlated with the densities of
Subselliflorae sea pen.
iii.
M. aequalis densities will be negatively correlated with the densities of California
Sea Cucumber Parastichopus californicus.
iv.
P. tesselatus densities will be negatively correlated with the densities of Shelf
Sponge.
v.
S. forreri densities will be positively correlated with the densities of Shelf
Sponges.
The null hypothesis was rejected for all Pearson’s correlation tests except one (correlation
between P. tesselatus and the shelf sponge) (Table 8). Five Pearson’s correlation tests did
have significant results with positive correlations greater than 0.6 except the correlation
between S. forreri and the shelf sponge (r = 0.58). In terms of the individual hypotheses
for each sea star species, no hypothesis was met except for the test between S. forreri and
the shelf sponge, although the correlation was only slightly over 0.5 (Table 8). In the
original hypotheses, four species were speculated to be negatively correlated with the
invertebrate of interest, but their hypothesis were rejected by the Pearson’s correlation
test, which showed that all correlations were positive, opposite of what was predicted.
The highest correlation was between L. foliolata and Subselliflorae sea pen in ROV
Hammerhead dataset (r = 0.71), and the lowest correlation was between P. tesselatus and
the shelf sponge (r = 0.29).
95
DISCUSSION
This study has indicated that with all other environmental variables taken into
account, a selected number of sea stars species are correlated with benthic
macroinvertebrate community patterns on the Pacific Northwest continental shelf. In the
Delta dataset, four species were identified to be descriptive. The importance of the sand
star, Luidia foliolata, can be attributed to its close association with the substratum type
mud-mud (MM), which was determined to be one of the most important environmental
variables explaining different macroinvertebrate assemblage patterns. The close
association between MM and L. foliolata could suggest that mud habitat with L. foliolata
is even more unique, and the combination of MM and L. foliolata can provide better
views of patterns of assemblages residing in habitats dominated by mud. Furthermore, its
percent contribution was particularly high in assemblage F, an assemblage that was
mainly characterized by Subselliflorae sea pen, also a MM associated species. The
association of both the sand star and the Subselliflorae sea pen with mud habitats is likely
what lead to the high correlation between these species in the Pearson’s test. The blood
star, Henricia spp., was also identified to be correlated with overall invertebrate patterns,
and this can be attributed to the fact that they were characteristic species in two
assemblages that mainly consist of Siltcoos Reef and Coquille Bank stations. Coquille
Bank and Siltcoos Reef stations were geographically in close proximity, and since the
Henricia spp. was not a characteristic species in other three assemblages, Henricia spp.
might have been selected because it is indicative of latitudinal differences in invertebrate
communities. The vermillion star, Mediaster aequalis, was also selected, primarily
96
because it had the most widespread distribution of all five sea stars, and it was an
important characteristic species in assemblages that were distributed across all Grays
Bank Deep & Shallow, Siltcoos Reef, and Coquille Bank stations, potentially indicating
its correlation with a community of generalists. Finally, the cushion star, Pteraster
tesselatus, was possibly shown as a descriptive species, because it was an important
characteristic species only in an assemblage which consisted of five Siltcoos Reef
stations. The presence of P. tesselatus at Siltcoos Reef but not elsewhere could suggest
similar latitudinal variance as implied by Henricia spp. However, unlike Henricia spp., P.
tesselatus was not present in Coquille Bank. The absence of P. tesselatus in Coquille
Bank could also be associated with different rock material composition that may
contribute to distinct macroinvertebrate assemblages between Siltcoos Reef and Coquille
Bank stations. Another reason for the absence of P. tesselatus at the Siltcoos Reef could
be that this species is even more latitudinally confined.
Unlike the for Delta stations, for the ROV survey only two sea star species were
shown as descriptive species of general macroinvertebrate assemblage patterns. These
two species were L. foliolata, and the velcro star, Stylasterias forreri. L. foliolata was
once again shown as descriptive, because it is a species that is indicative of low-relief
fine sediment habitats, such as those primarily composed of mud. Habitats composed of
low-relief mud are known to have very distinct invertebrate communities in comparison
to habitats composed of high-relief rocky types. The latitude was also shown to be an
important variable in the subset with highest correlation. S. forreri was possibly shown as
97
an influential species because it was widely distributed in many stations across both
Grays Bank and Siltcoos Reef.
In the Delta stations, all correlation tests were significant except the test between
P. tesselatus and shelf sponge. Perhaps Henricia spp. was positively associated with
branching sponges, since it is possible that they would prefer feeding on smaller
encrusting sponges and zoanthid anemones that were not quantified by this study
(Mauzey et al. 1968). If Henricia spp. greatly depends on branching sponges for food
source, it would mean that they would have to climb onto branching structure of the
Poriferan to digest their outer tissues. Crawling onto these sponges would mean greater
exposure to currents, thus putting the Henricia spp. at risk of being swept away.
Furthermore, it might be energetically unfavorable for the Henricia spp. to climb onto a
branching sponge. L. foliolata was positively correlated with Subselliflorae sea pen
instead of negative as hypothesized, because this might suggest that their burrowing
behavior may not occur at minimal intensity and frequency to actually uproot
Subselliflorae sea pens from the sediment. Likewise, it may be possible that the
Subselliflorae have peduncle with muscles that are strong enough to adhere to the
sediment, and resistant to burrowing disturbance caused by L. foliolata, if such burrowing
activities do occur adjacent to the sea pen. The vermillion star M. aequalis was positively
correlated with red sea cucumber P. cailfornicus, contrary to the hypothesis. Although
carrion and other decaying matter do make up large portion of M. aequalis diet, M.
aequalis are also known to be formidable predators (Birkeland 1974). Their diet is also
known to change by season (Mauzey et al. 1968; Birkeland 1974). Perhaps the resource
98
partitioning in high-relief rocky habitats were M. aequalis and P. californicus cohabit is
well-balanced so that the two species can avoid interspecific competition. The cushion
star, P. tesselatus, was the only species whose null hypothesis for Pearson’s correlation
test was not rejected. P. tesselatus is known to feed on encrusting sponges, or the sponges
that cover rock layers without any particular morphological features (Mauzey et al. 1968).
Shelf sponges, although not branching, are usually flat, but sometimes come with various
morphological features that are sometimes pointed, crested, bent, etc. Since P. tesselatus
are fat, rotund, and have short stubby arms, an attempt to clamber over a pointed shape of
shelf sponge may be highly energetically unfavorable for P. tesselatus; thus they may be
feeding primarily on encrusting sponges rather than other Poriferans. Since quantifying
encrusting sponges is very difficult, mainly because often they are difficult to distinguish
from bare rock surface, it was possible to make observations of these organisms at the
Delta stations to explore this hypothesis.
In the ROV Hammerhead dives, the correlation tests for both L. foliolata and S.
forreri were positive. The same explanation for the correlation test result between sand
star L. foliolata and Subselliflorae sea pen in Delta dives can also be applied to the
correlation test results in ROV Hammerhead dives. The correlation test between S.
forreri and the shelf sponge was the only correlation test that met the hypothesis,
although the correlation was low. The limited literature that has been published about S.
forreri suggest that they specialize in preying on fish (Robilliard 1971; Chia and
Amerongen 1974; Lambert 2000). However, Lambert (2000) stated that S. forreri
alsofeed on sponges, suggesting that these species may feed on sponges as much as they
99
prey on fish, hence the low positive correlation between their densities and the densities
of shelf sponges.
Sea stars mainly exert their influence in community heterogeneity and diversity
through their feeding rate, prey selection, and other foraging strategies (Gaymer et al.
2004). Many sea stars have diverse feeding strategies among species and across seasons;
it is also possible that in one particular season, the sea stars would consume a prey in
lower frequency than they would consumer another prey species in a different season
(Birkeland 1974). The differences of influence that sea stars can exert on community
diversity also could depend on the habitat they primarily inhabit. In this study, three out
of five sea stars: Henricia spp., P. tesselatus, and S. forreri were associated with highrelief rocky habitats. These three species may be attracted to higher-relief rocky habitats
due to food availability, substrata, and shelter provided by sponge and gorgonian colonies.
Their predation of sponges and other organisms depending on the sponge colonies could
be playing a significant role in maintaining energy flow between organisms of different
trophic levels, since their predation may prevent one organisms taxa from becoming too
abundant, just as Pisaster ochraceus has demonstrated with its predation behavior in
intertidal habitats (Paine 1966).
The sand star, L. foliolata, was identified as a characteristic species because they
are associated with fine sediment habitats, which have many fewer associated taxa than
high-relief habitats. Mauzey et al. (1968) observed that L. foliolata have a diverse diet
that consists of various small Holothurians, bivalves, and even crustaceans. Since it is
known to capture its prey by digging into substrata, it can be inferred that L. foliolata
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mainly feeds on small infaunal invertebrates that usually cannot be observed in research
using underwater submersibles. Therefore, L. foliolata’s actual influence on community
diversity may be reflected on the infaunal invertebrates rather than epifaunal
macroinvertebrates.
Finally, M. aequalis could be influencing macroinvertebrate community diversity
through their highly varied diet. Mauzey et al. (1968) found that along with detritus, M.
aequalis also feeds on wide array of prey including but not limited to sponges, algae,
nudibranchs, sea pens, diatoms, dinoflagellates, hydroids, and bivalves. This
opportunistic behavior could make the M. aequalis responsible for community diversity
declines if they inhabited a low-relief fine sediment habitat with relatively low
macroinvertebrate diversity to begin with (i.e. a mud habitat occupied by sea pens and
several other macroinvertebrate taxa).
Sea stars undoubtedly have potential to influence the abundance and distribution
of various prey species (Menge 1972; Gaymer et al. 2004). Their ability to influence
overall community is determined by wide range of factors, including prey species
preferences (by age, habitat, etc.), prey size preference, prey capturing strategies, and
prey consumption percentages (i.e. whether they consume all the prey remains or leave
carrion for other species to scavenge). While the specific feeding habits and other life
history components of the potentially influential sea stars in the Pacific Northwest’s
continental shelf waters are still relatively unknown, with the assessment of their
contribution to distinct macroinvertebrate assemblages, their association with specific
substrata types, and their high correlation with invertebrate community patterns, the light
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on Pacific Northwest’s sea stars can be shed slowly as we steadily characterize the roles
of one of the most important and indistinguishable macroinvertebrate groups in benthic
continental shelf habitats.
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BIBLIOGRAPHY
Birkeland, C. 1974. “Interactions Between a Sea Pen and Seven of Its Predators.”
Ecological Monographs 44: 211–232.
Chia, F-S, and H. Amerongen. 1974. “On the Prey-catching Pedicellariae of a Starfish,
Stylasterias Forreri (de Loriol).” Canadian Journal of Zoology 53: 748–755.
Dayton, P.K. 1971. “Competition, Disturbance and Community Organization: The
Provision and Subsequent Utilization of Space in a Rocky Intertidal Community.”
Ecological Monographs 41: 351–389.
Dayton, P.K., G.A. Robillard, R.T. Paine, and L.B. Dayton. 1974. “Biological
Accommodation in the Benthic Community at McMurdo Sound, Antarctica.”
Ecological Monographs 44: 105–128.
Gaymer, C.F., C. Dutil, and J.H. Himmelman. 2004. “Prey Selection and Predatory
Impact of Four Major Sea Stars on a Soft Bottom Subtidal Community.” Journal
of Experimental Marine Biology and Ecology 313 (2): 353–374.
Greathead, C.F., D.W. Donnan, J.M. Mair, and G.R. Saunders. 2007. “The Sea Pens
Virgularia Mirabilis, Pennatula Phosphorea and Funiculina Quadrangularis:
Distribution and Conservation Issues in Scottish Waters.” Journal of the Marine
Biological Association of the UK 87: 1095–1103.
Lambert, P. 1997. Sea Cucumbers of British Columbia, Southeast Alaska, and Puget
Sound. Seattle, WA: University of Washington Press.
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———. 2000. Sea Stars of British Columbia, Southeast Alaska, and Puget Sound.
Vancouver, BC, Canada: UBC Press.
Loh, T.L., and J.R. Pawlik. 2009. “Bitten down to Size: Fish Predation Determines
Growth Form of the Caribbean Coral Reef Sponge Mycale Laevis.” Journal of
Experimental Marine Biology and Ecology 374 (1): 45–50.
Mauzey, K.P., C. Birkeland, and P.K. Dayton. 1968. “Feeding Behavior of Asteroids and
Escape Responses of Their Prey in the Puget Sound Region.” Ecological Society
of America 49 (4): 603–619.
Menge, B.A. 1972. “Foraging Strategy of a Starfish in Relation to Actual Prey
Availability and Environmental Predictability.” Ecological Monographs 42 (1):
25–50.
Paine, R.T. 1966. “Food Web Complexity and Species Diversity.” American Naturalist
100: 65–75.
Robilliard, G. 1971. “Feeding Behavior and Prey Capture in an Asteroid, Stylasterias
Forreri.” Syesis 4: 191–195.
Ruzicka, R., and D.F. Gleason. 2008. “Latitudinal Variation in Spongivorous Fishes and
the Effectiveness of Sponge Chemical Defenses.” Oecologia 154 (4): 785–794.
———. 2009. “Sponge Community Structure and Anti-predator Defenses on Temperate
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Sheild, C.J., and J.D. Witman. 1993. “The Impact of Henricia Sanguinolenta (O.F.
Müller) (Echinodermata:Asteroidea) Predation on the Finger Sponges, Isodictya
Sp.” Journal of Experimental Marine Biology and Ecology 166 (1): 107–133.
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CHAPTER II TABLES
A
3.21
2.27
C
2.88
6.62
2.14
Asteroid Echinoderm
Henricia sp.
Luidia foliolata
Mediaster aequalis
Poraniopsis inflata
Pteraster tesselatus
Asteroid Echinoderm
Henricia sp.
Luidia foliolata
Mediaster aequalis
Pisaster brevispinus
Pteraster tesselatus
Stylasterias forreri
Delta Assemblages
B
D
F
2.57
4.17
12.71
7.74
4.23
2.57
ROV Hammerhead Assemblages
D
E
F
1.73
5.72
3.68
3.44
1.76
2.38
1.57
2.5
2.26
G
14.83
-
G
7.19
3.81
-
Table 6 Contribution % of all sea stars across all assemblages in both Delta and ROV Hammerhead datasets.
These species were found within SIMPER’s 90% cutoff results. The hypotheses were made for only the
species that occurred in more than one assemblage.
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ROV
Delta
Dataset
Environmental Variables
BM, MM, RM, Depth, Latitude, L. foliolata , M. aequalis , Henricia sp., P. tesselatus
BM, MM, RM, Depth, Latitude, L. foliolata , M. aequalis , Henricia sp.
BM, MM, RM, RR, Depth, Latitude, L. foliolata , M. aequalis , Henricia sp., P. tesselatus
BM, FM, MM, RM, Depth, Latitude, L. foliolata , M. aequalis , Henricia sp.
BM, FM, MM, RM, RR, Depth, Latitude, L. foliolata , M. aequalis , Henricia sp., P. tesselatus
GG, RM, Latitude, L. foliolata , S. forreri
GG, RM, Temperature, L. foliolata , S. forreri
RM, Latitude, L. foliolata , S. forreri
GG, RM, Latitude, L. foliolata
GG, RM, Temperature, S. forreri
Correlation Coefficient
0.792
0.789
0.787
0.787
0.782
0.855
0.845
0.843
0.842
0.839
Table 7 Top five sets of environmental variables (with sea stars) that are most highly correlated with the
invertebrate structure in the Delta and ROV Hammerhead stations. Results were based on the BIO-ENV
results, after the sea stars were removed and added to the environmental matrix. All taxa densities were
square-root transformed, and all the environmental data were normalized (after substrata percentages were
log-transformed). For the full species names, refer to tables 1, 3, and 5.
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ROV
Delta
Dataset
Asteroid Echinoderm
Henricia sp.
Luidia foliolata
Mediaster aequalis
Pteraster tesselatus
Luidia foliolata
Stylasterias forreri
Species Compared
Branching Sponge
Subselliflorae
Parastichopus californicus
Shelf Sponge
Subselliflorae
Shelf Sponge
Correlation Coefficient
0.69
0.63
0.69
0.29
0.71
0.58
t
4.17
3.49
4.13
1.32
4.73
3.35
df
19
19
19
19
22
22
p-value
< 0.001
0.002
< 0.001
0.2015
< 0.001
0.003
Table 8 Pearson’s Correlation Test results between the influential sea stars and the invertebrate taxa of interest
at p = 0.05 significance level.
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