AN ABSTRACT OF THE THESIS OF
Alexander C. Carsh for the degree of Honors Baccalaureate of Science in Biology
presented on May 27, 2014. Title: The effects of interspecies interactions and
environmental conditions on biomass accumulation of sessile organisms within Oregon’s
rocky mid-intertidal habitats
Abstract approved: ______________________________________
Bruce Menge
With changing climate conditions and human impacts on ecosystems becoming a
big focus of study, it has become even more crucial to understand how our ecosystems
work. Community structure within rocky intertidal habitats is governed by a mix of
environmental conditions and species interactions. This project examined the effects of
different treatments designed to test three different methods of interspecies interaction:
predation, competition, and facilitation. We then examined the data in relation to the sites
where the samples were collected using MANOVA and linear-contrast analysis. We
found that biomass of barnacles, mussels, and algae often tended to be similar in different
treatments, suggesting that interspecies interactions were overall fairly weak. The site of
origin, on the other hand, had a consistent effect in determining biomass, with a general
pattern of northern sites accumulating more biomass than southern sites. We believe that
this is due to the interaction between upwelling strength and the width of the continental
shelf along the Oregon coast with regard to the roles they play in nutrient, phytoplankton,
and larval retention, leading to differences in growth rates.
Key words: Rocky intertidal, interspecies interactions, Oregon, upwelling, nutrients
Corresponding e-mail address: carsha@onid.orst.edu
©Copyright by Alexander C. Carsh
May 27, 2014
All Rights Reserved
The effects of interspecies interactions and environmental conditions on biomass
accumulation of sessile organisms within Oregon’s rocky mid-intertidal habitats
by
Alexander C. Carsh
A PROJECT
submitted to
Oregon State University
University Honors College
in partial fulfillment of
the requirements for the
degree of
Honors Baccalaureate of Science in Biology (Honors Scholar)
Presented May 27, 2014
Commencement June 2014
Honors Baccalaureate of Science in Biology project of Alexander C. Carsh presented on
May 27, 2014
APPROVED:
________________________________________________________________________
Mentor, representing Integrative Biology
________________________________________________________________________
Committee Member, representing Integrative Biology
________________________________________________________________________
Committee Member, representing Integrative Biology
________________________________________________________________________
Department Chair, Integrative Biology
________________________________________________________________________
Dean, University Honors College
I understand that my project will become part of the permanent collection of Oregon
State University, University Honors College. My signature below authorizes release of
my project to any reader upon request.
________________________________________________________________________
Alexander C. Carsh, Author
Acknowledgements
First and foremost, I’d like to thank my thesis mentor, Dr. Bruce Menge, for
guiding me through the process of writing an undergraduate thesis, including working
with graphs and statistical analyses. I would also like to thank the other members of my
thesis committee, Dr. Mark Novak and Jonathan Robinson, for providing useful input
towards improving my essay. Jonathan in particular provided useful insight into the more
technical aspects of my project.
My thanks also go out to Megan Poole, Lindsay Hunter, and Angela Johnson,
three research technicians I worked under through the years. They helped me integrate
into the lab environment and provided advice whenever I had an issue. Finally, I wish to
thank the various research technicians, graduate students, postdocs, interns, and student
volunteers working in the PISCO labs: you all made being in the lab such an enjoyable
and productive experience.
TABLE OF CONTENTS
Page
INTRODUCTION ...............................................................................................................1
Rocky intertidal zone – abiotic factors affecting organism growth .........................1
Interspecies interactions – biotic factors affecting species growth ..........................2
Research questions and hypotheses .........................................................................3
MATERIALS AND METHODS ........................................................................................4
Collection sites .........................................................................................................4
Annual recruitment dataset ......................................................................................5
Annual colonization experiment (ACE) ..................................................................5
Collection and processing ........................................................................................6
Statistical analyses ...................................................................................................7
RESULTS ............................................................................................................................9
2010 Annual Recruitment ........................................................................................9
2011Annual Recruitment .........................................................................................9
2012 ACE.................................................................................................................9
DISCUSSION ....................................................................................................................11
Answering the research questions ..........................................................................11
Potential explanations of observed results .............................................................11
Potential expansions and improvements ................................................................15
Conclusion .............................................................................................................15
LITERATURE CITED ......................................................................................................17
LIST OF FIGURES
Figure
Page
1.
Oregon Coast map................................................................................................. 19
2.
Diagrams of the treatments ....................................................................................20
3.
Graph of the 2010 annual recruitment data ...........................................................21
4.
Graph of the 2011 annual recruitment data ...........................................................22
5.
Graph of the 2012 ACE data ..................................................................................23
LIST OF TABLES
Table
Page
1.
MANOVA and linear contrast analysis of the 2010 AR data ...............................24
2.
MANOVA and linear contrast analysis of the 2011 AR data ................................25
3.
MANOVA of the 2012 ACE data .........................................................................26
4.
Summary of site, treatment, and site x treatment comparisons for the 2012 ACE
data ........................................................................................................................26
LIST OF ABBREVIATIONS
Dataset Code
AR
ACE
Site Code
CM
FC
BB
SR
YB
SH
Treatment
Code (ACE)
MP
FN
CG
-C
-M
Dataset
Annual Recruitment
Annual Colonization Experiment
Sample Site
Cape Meares
Fogarty Creek
Boiler Bay
Seal Rock
Yachats Bay
Strawberry Hill
Site Code
TK
CA
CB
POH
RP
Sample Site
Tokatee Klootchman
Cape Arago
Cape Blanco
Port Orford Head
Rocky Point
Treatment
Marked plot (control)
Fenced plot (mesh control)
Cage (predator exclusion)
Cage with cirriped (barnacle) removal
Cage with Mytilus (mussel) removal
1
The effects of interspecies interactions and environmental conditions on biomass
accumulation of sessile organisms within Oregon’s rocky mid-intertidal habitats
Introduction
Due to the current shift in global environmental conditions, it has become more
important than ever to learn how changing an organism’s living conditions can affect its
ability to grow and survive. This is especially true for rocky intertidal ecosystems, where
factors such as temperature, wave action, nutrient availability, and habitat type create
vastly different communities of organisms. Changes to any of these factors, whether from
natural or artificial causes, can potentially bring about drastic differences in the types of
organisms that can grow in a given location.
Rocky intertidal zone – abiotic factors affecting organism growth
Because of intensive research within rocky intertidal habitats, the effects of
various individual factors in structuring communities are well-known, in particular how
the distinct zones of the intertidal form. A long-standing model suggests that the lower
limit of an organism’s potential living range in these habitats tends to be determined by
biotic factors like competition and predation, while upper limits are determined by abiotic
factors like temperature causing physiological stress on the organism (Connell 1972).
For example, large, fleshy algae species tend to live within low areas along the
shoreline because they are susceptible to desiccation and photoinhibition when exposed
to air and sunlight (Dayton 1971; Apprill and Lesser 2003; Kavanaugh et al. 2009).
2
However, barnacles are more resistant to desiccation and can live in the high intertidal
(Foster 1971), avoiding some of the other pressures of lower zones such as intense
predation or competition.
Interspecies interactions – biotic factors affecting species growth
Biotic factors can play a role in determining where organisms can survive. In
rocky intertidal habitats, space is a limiting resource for sessile invertebrates and
macroalgae, so the ability to compete for space may determine how successful different
organisms will be (Dayton 1971). As the dominant competitors along the Oregon Coast,
mussels such as Mytilus californianus crowd out local species of barnacles (Menge 1976,
Lively and Raimondi 1987), resulting in mussel beds dominating the mid-intertidal
zones. Due to the role of limiting resources in how competition operates, competition
effects are greater in heavily-populated sites (where resources are in greater demand) and
lower when organisms are sparse.
Mussel populations are kept in check by predators, most notably the sea star
Pisaster ochraceus (Paine 1966, 1974, Menge et al. 1994). Pisaster is prone to
desiccation and thermal stress (e.g., Petes et al. 2008, Szathmary et al. 2009, Pincebourde
et al. 2009) but is mobile, and thus prefers to live in the low intertidal zone. This creates a
distinct band of space or “refuge” where mussels can dominate: above that range, low
tide exposure will lead to thermal stress and eventual desiccation, while living too close
to the low tide water line leaves them more vulnerable to predation from sea stars.
Predation or grazing can also affect barnacles and macroalgae (Connell 1961, Dayton
3
1971, Menge 1976), but due to these organisms being non-dominant space competitors,
the effects are less pronounced.
A third type of species interaction, facilitation, can also play a role in determining
what can grow in such conditions (e.g. Bruno et al. 2003). Unlike the other examples,
facilitation occurs when the presence of one species or group of species allows other
groups to perform better, and even survive where they normally would do poorly or die.
For example, smaller macroalgal species tend to be extremely vulnerable to desiccation,
greatly limiting where they can grow; however, the presence of larger macroalgae in the
same spot can create a canopy for the smaller species, protecting them from the sun’s
rays and allowing them to live higher along the coast (Watanabe et al. 1992). Another
commonly seen example is where the growth of barnacles on smooth, bare rock can
provide a rough-textured substratum to which mussel and barnacle larvae and algal
spores can more easily attach (Menge 1976, Menge et al. 2011).
Research questions and hypotheses
For my project, I tested the effects of competition, predation and facilitation with
respect to variation among sites along the coast to determine their impacts on sessile
organisms in Oregon’s rocky mid-intertidal habitats, answering the following questions:
1. How do competition, predation, and facilitation affect the annual accumulation of
biomass of sessile organisms living in the mid zone of Oregon’s rocky intertidal?
2. How do these effects differ between different sites along the Oregon coast?
3. Do these relationships vary over time?
4
Materials and methods
Collection sites
Samples were collected from eleven sites at five capes along the Oregon Coast
(Figure 1; see Menge et al. unpublished manuscript for detailed information on the
environmental conditions at these sites). The northernmost study site is located at Cape
Meares (CM) (45.502°N, 123.954°W). Cape Meares is a rocky shelf that drops steeply
from the upper section of the mid-intertidal mussel bed to the sea. As the northernmost
site, Cape Meares receives the weakest upwelling of any site studied.
The next cape southward is Cape Foulweather (44.83°N, 124.06°W), which
contains two study sites, Fogarty Creek (FC) and Boiler Bay (BB). The habitat around
Cape Foulweather is known for lower levels of nutrient retention due to the narrow
continental shelf. Benches at both sample sites have solid, gently sloping, uniform rock
surfaces, with little sand and a few surge channels.
The next cape southward is Cape Perpetua (44.287°N, 124.114°W), a large cape
containing four study sites: Seal Rock (SR), Yachats Beach (YB), Strawberry Hill (SH),
and Tokatee Klootchman (TK). Cape Perpetua is located next to a broad section of the
continental shelf, resulting in high nutrient and larval retention. Except for Seal Rock,
which is a steep rocky outcrop, sites at Cape Perpetua contain solid yet uneven rock
surfaces as well as areas covered in sand and small pebbles with a gentle slope, creating
some variance in habitat.
5
Cape Arago (CA) is next southward (43.412°N, 124.454°W). This site slopes
seaward and has several deep channels, but has a relatively homogeneous substratum,
except in the low macroalgal zone where the substratum is highly heterogeneous.
The southernmost cape is Cape Blanco (42.838°N, 124.564°W), which is the
location of three study sites: Cape Blanco Main (CB), Port Orford Head (POH), and
Rocky Point (RP). Cape Blanco is the southernmost area of study, and so receives the
strongest upwelling of all the sites. For more information on each of these sites, see
Menge et al. (1994, 2004).
Annual recruitment dataset
From 2009 to 2011, biomass accumulation was quantified at each of the eleven
sites. For each sample, we first cleared 15x15cm plots of all organisms. Five plots then
had mesh cages (CG; Figure 2, photo A) placed around them to exclude predators (e.g.
whelks, sea stars), while the other five plots were marked at each corner but otherwise
unmanipulated (marked plots, MP; Figure 2, photo B) and served as controls. Each plot
was prepared in late spring to early summer of the year.
Annual colonization experiment (ACE)
In 2012, the project expanded in order to test for other types of interspecies
interactions, which involved six of the above study sites, two each from the three major
capes (FC and BB for Cape Foulweather, YB and SH for Cape Perpetua, and CB and RP
for Cape Blanco). In addition to cages and marked plot controls, we included three other
6
treatments. To test for potential mesh artifact effects, we deployed fence controls (FN;
Figure 2, photo C), which were half-cages (two adjacent sides rather than all four).
Comparison between FN and MP results allows a test for the possible influence of mesh
presence, since neither treatment prevented the entry of predators. The other two
treatments were full cages (Figure 2, photo B), from which we removed barnacle recruits
(-C) or mussel recruits (-M). Since barnacles are prime facilitators along the Oregon
intertidal, cages with barnacle removal allowed us to test for the effects of facilitation.
Similarly, with mussels being the dominant competitors, the mussel removal cages
allowed us to test the ability of barnacles to survive in the absence of competition (and
predators). In reality, bad weather conditions and high mussel recruitment at Cape
Perpetua sites make it unfeasible to remove all mussels from –M plots, so these
treatments are best considered to be mussel reductions instead of mussel removals.
Collection and processing
All plots were re-cleared after one year, and accumulated biomass was brought
back to the lab and frozen for later processing. Processing involved thawing each sample,
sieving to wash out sediment, and sorting each sample into separate pre-weighed tins by
category [barnacle, mussel, algae, and other (e.g. polychaetes, anemones)], then placed in
a drying oven at 80oC. After one week, they were removed from the oven and reweighed
to determine dry weight (in grams).
7
Statistical analyses
Microsoft Excel 2010 software was used to organize data and perform the
transformation calculations. JMP 8.0 statistical software was used to perform the
statistical analyses. SigmaPlot 10.0 was used to create the graphs of the data.
Calculations were first performed on the data to determine the absolute dry
weights of the subsample. After initial graphs made it clear that the data would be better
represented after transformation, we ran natural log transformations on the data. These
transformed data were then graphed. At the time of writing, not all samples collected had
been processed; therefore, while the 2010 annual recruitment data included all eleven
sites, the 2011 data only included eight sites (all but FC, YB, and RP) and the 2012 data
included five out of six ACE sites (all except BB).
For each year, a multivariate analysis of variance (MANOVA) test was first run
on the natural log transformed data to determine the effects of site, treatment, and
site-treatment interactions on biomass of four groups: barnacles, mussels, algae and
“other”. MANOVA is most appropriate for community data because it includes the
responses of multiple groups (i.e., the “community”), thus including possible effects of
interactions among the functional groups). We analyzed the effects of site, treatment, and
site*treatment in all datasets.
If the site*treatment interaction was not statistically significant (as was the case in
our 2011 data), linear contrasts were used to test for differences in relative biomass levels
by site and by treatment as main effects. If the site*treatment interactions were significant
(such as in our 2010 and 2012 sample sets), linear contrasts were done among or between
8
treatments by each site to determine which combinations were significant. We also used
linear contrasts across sites in the 2012 ACE data to determine how biomass varied by
site independent of treatment.
9
Results
2010 Annual Recruitment
For the 2010 annual recruitment data, the MANOVA test showed that the effect
of treatment varied by site (i.e., the site*treatment interaction was statistically significant;
p=0.0001), so each site was tested individually to determine if there were differences
between the two treatments (Table 1, Figure 2). Further analysis revealed that cage and
marked plot treatments differed at four sites: FC (p<0.0001), SR (p=0.0008), TK
(p=0.0022), and RP (p=0.0028). Of these, all but FC had higher biomass in the cages as
expected.
2011 Annual Recruitment
The MANOVA test for 2011 showed that biomass varied among sites and
treatments as main effects (p<0.0001 and p=0.0312, respectively; the site*treatment
interaction, p = 0.21) (Table 2, Figure 3). Therefore, linear contrast analyses were
performed on both variables. We found that samples from CM, BB, SR, SH, and TK had
higher levels of biomass than samples from POH, CB, and CA. We also found that
samples from cages contained more biomass than samples from marked plots (Table 2).
2012 ACE
As with the 2010 data, the effects of treatments in the ACE experiment varied
among sites (Table 3, site*treatment interaction, p <0.0001, Figure 4). Using linear
10
contrasts, we found that abundances in MP (marked plot) and FN (fence control) differed
at YB (p=0.013), and RP (p=0.0009), but not at other sites (Table 4); that is, the presence
of mesh only showed an effect at those two sites. Thus, for YB and RP, we used the FN
treatment as the control for further comparisons among treatments involving controls; for
the other three sites, the FN and MP treatments were combined.
Tests for the effect of predation on community biomass compared CG (cage,
predators reduced, mussel-barnacle interactions allowed) treatments vs. MP and/or FN
treatments. ). CB was the only site at which predation effects were found to be significant
(p<0.0001) (Table 4).
The CG treatments were then compared separately to both the –M and –C
treatments to determine the effects of mussel and barnacle removal on competition and
facilitation, respectively. However, neither treatment had an effect on community
biomass at any site.
Linear contrasts for the ACE experiment showed that, ignoring the different
treatments, SH, YB, and FC had higher levels of biomass than RP and CB. SH also had
higher levels of biomass than FC.
11
Discussion
Answering the research questions
Concerning the role that predation, competition, and facilitation play in Oregon’s
rocky intertidal, we found that predation had a significant impact at some sites over all
three years, but competition and facilitation showed no effect on community biomass.
On the other hand, site showed consistent effects on the biomass accumulation of
the organisms. The location of each sample also seems to have affected the effectiveness
of some treatments as well: both 2010 and 2012 data showed differences of predation
effects based on site. Additionally, the mesh effect tested in 2012 differed in magnitude
by site.
The differences between the three years seem to indicate that effects of species
interactions vary through time. However, because the samples only span three years, and
many geologic, biologic, and oceanographic processes run in decades-long cycles (if not
longer), we cannot come to any firm conclusions about the effects of time based on the
data in this study alone.
Potential explanations of observed results
The most likely cause for why there were no significant differences between cage
treatments (predators absent, colonization of barnacles and mussels allowed) and the cage
with barnacle or mussel removal treatments is the overall low recruitment of biomass in
12
these sites, especially at southern sites. As I mentioned earlier in the paper, competition
in particular is based on species having to jointly strive for limited resources (Dayton
1971). If there are not enough organisms in an area to limit any particular resource (in
this case, available space), competition is unlikely to be important. Similarly, facilitation
is also dependent on having large masses of organisms upon which other organisms can
gain a foothold over bare rock, so lower levels of organisms overall would result in
facilitation being less impactful. This would mean that we would expect to see treatments
have lower impact at southern sites; based on the 2010 data, that appears to be the case,
since three of the four sites with differences between the CG and MP treatments were
from northern capes. Results from the ACE data are a bit less clear in this regard, but
seeing as how only one treatment testing interspecies interactions showed an effect, and
only at one site (predation at CB), it may just be a random outlier.
We also recognize that the weak effects of both competition and predation may
have been due in part to inconsistent removal of barnacles and mussels from the
treatments during the collection process. Due to weather and tidal conditions, it was often
hazardous to travel to the coast, especially during the winter months before collection.
Because of this, mussels and barnacles were not removed as often as planned, so there
may have been some competition and facilitation effects still present, lowering the
difference between those treatments and the cages. However, we believe that there was
enough consistency in our continued removal of these organisms that the effects of
facilitation and competition were sufficiently altered to detect resulting changes in
biomass accumulation.
13
Unlike the other two interactions we examined, predation did show an effect on
biomass accumulation. We believe that this is because the direct effects of predation (i.e.
lowering the population of the prey species) would still have an impact as long as
predators and prey were both present in an area, regardless of population density.
However, predation in these systems has an indirect effect on non-dominant competitors:
mussel predation frees up space for barnacles and algae to settle on, relieving some
competition pressure. Because competition was found to have little to no effect in our
samples, this indirect effect of predation would also be quite weak when compared to
areas with more population density.
When comparing the different sites to determine the effects of each, we noticed
that a general trend emerged of biomass accumulation differing between northern and
southern sites. At least three potential factors may explain this pattern. Sea surface
temperature (SST) can affect invertebrate growth, and thus is a candidate explanatory
variable. However, previous studies have shown that overall, moderate increases in
temperature can increase biomass production through Q10 effects (Menge et al. 2008),
which, based on typical temperature-latitude relationships, would produce the opposite
effect on growth than the one observed in this study, because water temperatures tend to
be warmer southward and cooler northward (Schoch et al. 2006). In this case, however,
mean SST does not appreciably differ between the northernmost and southernmost capes
in the study (Menge et al., unpublished manuscript), meaning temperature likely played
no role in our results.
Two additional factors include upwelling strength and a variable continental shelf
width. We suggest that these factors work in tandem to underlie the north-south variation
14
in biomass accumulation. Overall, the Oregon coast experiences intermittent upwelling,
with periods of upwelling and downwelling occurring all along the coast. However,
northern sites along the coast experience weaker upwelling than more southern sites
creating some variation between the sites (Iles et al. 2012, Menge et al., unpublished
manuscript).
By itself, latitudinal differences in upwelling would seem to indicate that
organisms at southern sites should have greater biomass accumulation than northern sites
due to increased influx of nutrients and planktonic larvae. However, strong upwelling
also increases the efflux of these same particles from the system, and the width of the
continental shelf determines the potential for larvae and nutrient retention at each site.
Since the continental shelf along the Oregon coast narrows from north to south (Figure
1), higher larval/nutrient retention would occur during periods of upwelling at northern
sites than at southern ones, which suggests higher food availability for sessile filter
feeders like mussels and barnacles, and thus faster growth rates to the north. This
interpretation is consistent with the data collected in this study. This explanation also
helps explain the outlier to the trend in the data as well. SH was found to have a
statistically higher amount of biomass than FC in the 2012 data, contradicting the
otherwise-established trend. However, the continental shelf around Cape Foulweather
narrows before broadening out again near Cape Perpetua, so this result remains consistent
with the explanation provided by upwelling and the continental shelf.
15
Potential expansions and improvements
For future experiments conducted in this field, I believe the major improvement to
be made would be to expand the experiment over several more years to track the impacts
of these effects over time. The impacts of oceanographic cycles (such as the Pacific
Decadal Oscillation) make long-term tracking of coastal systems especially important.
It might also be worthwhile to see if the results differed between sites with
different ecosystems. Other studies have noted an inverse relationship between
macrophyte and invertebrate abundance at different sites (Menge et al. 1997, 2004, 2011,
Menge et al., unpublished manuscript). Cape Foulweather and Cape Perpetua serve as
notable examples of this: while Foulweather sites tend to be dominated by algae, sites
along Perpetua tend to be more invertebrate-dominant. These two different community
structures might lead to differences in magnitude of both environmental impacts and
interspecies interactions, so further studies might test to see if there are any differences
present.
Finally, collaborating to create projects with larger scopes, spanning much larger
regions of the coast, might better reflect the effects of site variations along the coast.
Having more sites studied would allow for better relationships to be established between
how the conditions vary and how the biomass accumulation changes as a result.
Conclusion
In conclusion, relatively low accumulation of biomass overall prevented
interspecies interactions from playing a large role in the growth of the organisms studied,
16
especially at the sites along the southern Oregon coast. However, there were noticeable
differences in biomass based on site conditions, correlating well with upwelling strength
and continental shelf width. This stresses the importance of examining the effects of
changing climate/environmental conditions at local and regional scales, since different
sites may vary in response based on their already-established structure.
17
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Watanabe, J. M., Phillips, R. E., Allen, N. H., Anderson, W. A. (1992) Physiological
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19
Figure 1. A map of the Oregon Coast, with stars indicating the capes from which the
samples in the study were collected. Also visible on this map is the continental shelf
directly off the coast; the shelf gradually narrows from north to south, with a distinct
narrow region around Cape Foulweather.
20
Figure 2. A diagram showing the three different treatment structures used in this study.
Photo A depicts a 15x15cm plot marked off at each corner, but otherwise unmanipulated
(MP treatments). Photo B shows an example of the mesh cages that surrounded three
treatments (CG; the same types of cages were used for –C and –M in the ACE project).
Photo C shows one plot from the half-cage (FN) treatment that was introduced in the
ACE project. Note that these photos were taken two months after the plot were initially
cleared, so some biomass has already accumulated at each one. 21
5
A. CM
E. YB
I. CB
B. FC
F. SH
J. POH
C. BB
G. TK
K. RP
D. SR
H. CA
4
3
2
1
0
5
4
3
ln Biomass
2
1
0
5
4
3
2
1
0
5
4
Cage
MP
barnacles
mussels
algae
other inverts
3
2
1
0
Cage
MP
Cage
MP
Figure 3. These graphs display the natural log-transformed absolute biomass (g) data for
the 2010 annual recruitment, with the error bar representing 1 standard error above the
mean. Sites are labeled A-K with respect to their relative positions (A being the
northernmost site, K being the southernmost). Within this dataset, treatments differed for
four sites: FC (p<0.0001), SR (p=0.0008), TK (p=0.0022), and RP (p=0.0028) (see Table
1).
22
5
A. CM
E. TK
4
3
2
1
0
5
B. BB
F. CA
C. SR
G. CB
D. SH
H. POH
4
3
ln Biomass
2
1
0
5
4
3
2
1
0
5
4
3
2
1
0
Cage
MP
Cage
barnacles
mussels
algae
other inverts
MP
Figure 4. These graphs display the natural log-transformed absolute biomass (g) data for
the 2011 annual recruitment, with the error bar representing 1 standard error above the
mean. Sites are labeled A-H with respect to their relative positions (A being the
northernmost site, H being the southernmost). The site-treatment interaction for these
sites was found to be insignificant (p=0.2124). Generally, northern sites had more
biomass than southern sites (p<0.0001), and cages had more than MP (p=0.0312) (see
Table 3). 23
6
5 A. FC
4
3
2
1
0
ln biomass
6
5
4
3
2
1
0
6
5
4
3
2
1
0
6
5
4
3
2
1
0
6
5
4
3
2
1
0
barnacles
mussels
algae
other inverts
B. YB
C. SH
D. CB
E. RP
MP
e
nc
Fe
ge
Ca
us
arn
m
b
e
g
ge
Ca
Ca
Figure 5. These graphs display the natural log-transformed absolute biomass (g) data for
the 2012 ACE, with the error bar representing 1 standard error above the mean. Sites are
organized from north to south. Significant difference between treatments were found
between the MP and fence treatments at both YB (p=0.013) and RP (p=0.0009), and
between the combined controls (MP and fence) and cage treatments at CB (p<0.0001)
(see Tables 3 and 4).
24
Table 1. Biomass in annual recruitment experiment, 2010. Identity MANOVA testing
the response of barnacles, mussels, and algae (ln transformed) by site, treatment, and
site*treatment.
Site
Treatment
Site*Treatment
Wilks Lambda
0.08842935
0.18892268
0.43047035
Approx. F
4.47194149
5.62541725
2.44840505
NumDF
63
30
30
DenDF
224.7
220.8
220.8
p
<0.0001
<0.0001
0.0001
CM S*T
FC S*T
BB S*T
SR S*T
YB S*T
SH S*T
TK S*T
CA S*T
CB S*T
POH S*T
RP S*T
F-test
0.05833984
0.34908195
0.05064866
0.24913125
0.01956417
0.05394568
0.21288118
0.01112408
0.07761312
0.02834014
0.20507047
1.45849594
8.72704871
1.26621647
6.22828129
0.48910429
1.34864198
5.32202958
0.27810202
1.94032804
0.7085035
5.12676179
3
3
3
3
3
3
3
3
3
3
3
75
75
75
75
75
75
75
75
75
75
75
0.2327
<0.0001
0.2921
0.0008
0.6908
0.2651
0.0022
0.8410
0.1303
0.5499
0.0028
25
Table 2. Biomass in annual recruitment experiments, 2011. Identity MANOVA testing
the response of barnacles, mussels, and algae (ln transformed) by site, treatment, and
site*treatment.
Site
Treatment
Site*Treatment
Test & Value
λ 0.22750951
F 0.18021007
λ 0.63247406
Approx.F
4.9069
3.1837
1.2581
NumDF
21
3
21
Site differences: CM = BB = SR = SH = TK > POH = CB = CA
Treatment differences: Cage > Marked Plot
DenDF
152.74
53
152.737495
p
<0.0001
0.0312
0.2124
26
Table 3. Biomass in annual colonization experiment, 2012. Identity MANOVA testing
the response of barnacles, mussels, and algae (ln transformed) by site, treatment, and
site*treatment. Treatments were marked plot (control, predators present), partial fence
(control for mesh effect, predators present), cage (predators absent, space competition
allowed), cage – barnacles (predators absent, barnacles reduced), and cage – mussels
(predators absent, mussels reduced).
Site
Treatment
Site*Treatment
Test & Value
λ 0.11834561
λ 0.20851616
λ 0.25883351
Approx.F
17.8057531
11.6077211
2.32647306
NumDF
12
12
48
DenDF
172.265338
172.265338
194.120137
p
<0.0001
<0.0001
<0.0001
Table 4. Biomass analysis. Summary of comparisons among treatments by site, testing
the Site*Treatment interaction shown in Table 3. When the mesh effect was significant,
the test for a predation effect used the fence control; otherwise, marked plot and fence
controls were combined for this test. Comparisons for mesh effect and predation effect
were made using linear contrasts after the identity MANOVA shown in Table 3 was run.
Comparisons for facilitation effect were made using linear contrasts after a two way
ANOVA testing differences in mussel biomass in cages and cages-barnacles.
Comparisons for competition effect were made using linear contrasts after a two way
ANOVA testing differences in barnacle biomass in cages and cages-mussels. α = 0.05.
Site
Fogarty Creek
Yachats Beach
Strawberry Hill
Cape Blanco
Rocky Point
Mesh effect Predation
Facilitation
(MP vs
effect (controls effect (mussels
Fence?)
vs cage?)
in Cage-barn vs
Cage?)
p = 0.12
p = 0.47
p = 0.83
p = 0.013
p = 0.18
p = 0.13
p = 0.98
p = 0.72
p = 0.24
p = 0.98
p < 0.0001
p = 0.08
p = 0.0009
p = 0.10
p = 0.19
Competition
effect (barnacles
in cage-mus vs
cage?)
p = 0.84
p = 0.16
p = 0.84
p = 0.10
p = 0.84
Total Biomass (ignoring treatment): SH = YB = FC > RP = CB; SH > FC.