Singing River Island, Mississippi Sound Gulf Sturgeon
Critical Habitat Benthic Community Assessment, 2005
SUBMITTED TO:
U.S. Army Corps of Engineers, Mobile District
P.O. Box 2288-0001
Mobile, AL 36628-0001
PREPARED BY:
Barry A. Vittor & Associates, Inc.
8060 Cottage Hill Rd.
Mobile, Alabama 36695
(251) 633-6100
September 2005
TABLE OF CONTENTS
LIST OF TABLES ......................................................................................................................... 3
LIST OF FIGURES .......................................................................................................................4
INTRODUCTION..........................................................................................................................5
METHODS .....................................................................................................................................5
Benthic Station Arrangement .............................................................................................5
Sample Collection And Handling .......................................................................................6
Hydrographic Data Collection............................................................................................6
Sediment Analysis ...............................................................................................................6
Macroinfaunal Sample Analysis ........................................................................................6
DATA ANALYSIS .........................................................................................................................7
Assemblage Structure .........................................................................................................7
HABITAT CHARACTERISTICS ...............................................................................................8
BENTHIC COMMUNITY CHARACTERIZATION................................................................9
HISTORIC COMPARISONS.....................................................................................................11
LITERATURE CITED ...............................................................................................................12
APPENDIX I - Station coordinates, August 2005
APPENDIX II - Benthic station hydrography
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LIST OF TABLES
Table 1. Summary of sediment data for the Mississippi Sound stations, August 2005.
Table 2. Summary of overall abundance of major benthic macroinfaunal taxonomic
groups for the Mississippi Sound stations, 2005.
Table 3. Summary of abundance of major benthic macroinfaunal taxonomic groups by
station for the Mississippi Sound stations, 2005.
Table 4. Distribution and abundance of benthic macroinfaunal taxa for the Mississippi
Sound stations, 2005.
Table 5. Percentage abundance of dominant benthic macroinfaunal taxa (> 10% of the
total) for the Mississippi Sound stations, 2005.
Table 6. Summary of benthic macroinfaunal data for the Mississippi Sound stations,
2005.
Table 7. A comparison of sediment and biological parameters from Mississippi Sound
stations collected in both 1980 and 2005.
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LIST OF FIGURES
Figure 1. Map of the Mississippi Sound stations, August 2005.
Figure 2. Sediment texture data for the Mississippi Sound stations, August 2005.
Figure 3. Sediment percent total organic carbon (%TOC) data for the Mississippi Sound
stations, August 2005.
Figure 4. Relative abundance of major taxa for the Mississippi Sound stations, August
2005.
Figure 5. Taxa richness data for the Mississippi Sound stations, August 2005.
Figure 6. Station density data for the Mississippi Sound stations, August 2005.
Figure 7. Taxa diversity (H') for the Mississippi Sound stations, August 2005.
Figure 8. Taxa evenness (J') for the Mississippi Sound stations, August 2005.
Figure 9. Hierarchical cluster analysis for the Mississippi Sound stations, August 2005.
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INTRODUCTION
Through TetraTech, Inc.’s environmental services contract with the United States
Army Corps of Engineers, Mobile District (COE), the COE contracted Barry A. Vittor &
Associates, Inc. (BVA) to characterize the benthic macroinfaunal community in the
vicinity of Singing River Island, Mississippi Sound, Pascagoula, Mississippi during
August 2005. The National Marine Fisheries Service (NMFS) has indicated that the Gulf
Sturgeon (Acipenser oxyrhynchus desotoi) may utilize this area for feeding during
migration between the Gulf of Mexico and the Pascagoula River. Navigation dredging
and dredge disposal activities in the general area may also impact the benthic
macroinvertebrate assemblages and affect potential sturgeon food resources. The data
collected from this study will be used to expand the understanding of the distribution of
Gulf Sturgeon critical habitat so that more informed management decisions pertaining to
dredging and dredge disposal operations can be made by the COE and NMFS.
METHODS
Benthic Station Arrangement
The benthic sampling plan was designed to provide pattern analysis throughout an
area that extended from West Pascagoula River on the west to Bayou Casotte on the east,
and from the lower reaches of West Pascagoula River on the north to the Gulf
Intracoastal Waterway on the south. One hundred (100) stations were established using a
symmetrical grid approach; locations of these sampling points are depicted in Figure 1
and station coordinates are compiled in Appendix I. Twelve of the 100 stations
represented points that were sampled by BVA in Fall 1980 and Spring 1981 for the COE,
and were intended to provide an indication of temporal variation in benthic community
composition. Geographic coordinates were pre-designated and programmed into BVA’s
Trimble® GPS unit to facilitate navigation to each station. In some cases, grid points
were found to be located in very shallow water (i.e. < 0.6 m) or on oyster bottoms and
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could not be sampled. Such stations were relocated to more suitable points and corrected
coordinates were recorded.
Sample Collection And Handling
A petite ponar grab (area = 0.023 m2) was used to collect bottom samples for
macroinfauna and sediment analysis at each of 100 Mississippi Sound stations during
August 2005. Macroinfaunal samples were sieved through a 0.5–mm mesh screen and
preserved with 10% formalin. Macroinfaunal samples were transported to the BVA
laboratory in Mobile, Alabama. Sediment texture and total organic carbon (TOC)
samples were places on ice for transportation to the laboratory.
Hydrographic Data Collection
Data recorded at each of the 100 stations included date, water depth, water
temperature, salinity and sea state. Hydrographic measurements were obtained with a
YSI Model 6600 water quality meter. Hydrographic data are provided in Appendix II.
Sediment Analysis
Sediment texture was determined at half-phi intervals using the hydrometer
technique for fractions smaller than 44 µm and nested sieves for larger particle fractions.
Texture parameters that were computed included percent gravel, sand, and silt /clay.
Total organic carbon (TOC) content was measured as ash-free dry weight expressed as a
percentage.
Macroinfaunal Sample Analysis
In the laboratory of BVA, benthic samples were inventoried, rinsed gently
through a 0.5 mm mesh sieve to remove preservatives and sediment, stained with Rose
Bengal, and stored in 70% isopropanol solution until processing. Sample material
(sediment, detritus, organisms) was placed in white enamel trays for sorting under Wild
M-5A dissecting microscopes. All macroinvertebrates were carefully removed with
forceps and placed in labeled glass vials containing 70% isopropanol. Each vial
represented a major taxonomic group (e.g. Polychaeta, Mollusca, Arthropoda). All sorted
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macroinvertebrates were identified to the lowest practical identification level (LPIL),
which in most cases was to species level unless the specimen was a juvenile, damaged, or
otherwise unidentifiable. The number of individuals of each taxon, excluding fragments,
was recorded. A voucher collection was prepared, composed of representative
individuals of each species not previously encountered in samples from the region.
DATA ANALYSIS
All data generated as a result of laboratory analysis of macroinfauna samples were
first coded on data sheets. Enumeration data were entered for each species according to
station and replicate. These data were reduced to a data summary report for each station,
which included a taxonomic species list and benthic community parameters information.
Archive data files of species identification and enumeration were prepared.
Assemblage Structure
Several numerical indices were chosen for analysis and interpretation of the
macroinfaunal data. Infaunal abundance is reported as the total number of individuals per
station and the total number of individuals per square meter (= density). Taxa richness is
reported as the average number of taxa represented in a given station collection.
Taxa diversity, which is often related to the ecological stability and environmental
"quality" of the benthos, was estimated using Shannon’s Index (Pielou, 1966), according
to the following formula:
s
H' = - ∑ pi(ln pi)
i=1
where, S = the number of taxa in the sample,
i = the i'th taxa in the sample, and
pi = is the number of individuals of the i'th taxa divided by the total number of
individuals in the sample.
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Taxa diversity within a given community is dependent upon the number of taxa
present (taxa richness) and the distribution of all individuals among those taxa
(equitability or evenness). In order to quantify and compare the equitability in the fauna
to the taxa diversity for a given area, Pielou's Index J' (Pielou, 1966) was calculated as J'
= H'/lnS, where lnS = H'max, or the maximum possible diversity, when all taxa are
represented by the same number of individuals; thus, J' = H' /H' max.
Cluster analysis of the Mississippi Sound data was performed by calculating the
Bray-Curtis similarity coefficient for all pairs of stations, having log transformed the
original taxa abundances to meet normality assumptions (Clarke and Gorley 2003).
Clusters were formed using the group-average linkage method between similarities
(Clarke and Gorley 2003).
HABITAT CHARACTERISTICS
Water depths at the benthic stations ranged from 0.70 m at Station PA003 in the
northwest part of the study area, to 6.61 m at Station PA056, which was located near the
west side of Pascagoula River navigation channel. Near-bottom salinities were relatively
high and exceeded 24 ppt at 68 of the 100 stations. Lower salinities occurred at the
shallower northern stations with a low of 8.2 ppt at Station PA003. Water temperatures
near-bottom were greater than 30°C at all but 14 stations, and were normal for this
season.
Sediment data for the 100 Mississippi Sound stations are given in Table 1 and
Figures 2 and 3. Sediment composition ranged from > 99% sand to > 98% silt+clay
(Table 1; Figure 2). The total organic carbon (TOC) fraction of the sediment was
uniformly low (<2.5%) at all stations (Table 1; Figure 3).
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BENTHIC COMMUNITY CHARACTERIZATION
Microsoft ™Excel electronic spreadsheets are being provided separately to the
Corps which include: raw data on taxa abundance and density for each station, a
complete taxonomic listing with station abundance and occurrence, a major taxa table
with overall taxa abundance, and an assemblage parameter table including data on
number of taxa, density, taxa diversity and taxa evenness by station.
Station location data for the 100 Mississippi Sound stations are given in Figure 1
and Appendix 1.
A total of 3577 organisms, representing 197 taxa, were identified from the 100
Mississippi Sound stations (Table 2). Polychaetes were the most numerous organisms
present representing 55.8% of the total assemblage, followed in abundance by
malacostracans (15.7%). Polychaetes represented 40.6% of the total number of taxa
followed by malacostracans (23.4%), bivalves (13.7%) and gastropods (12.7%) (Table 2).
The abundance of major taxa by station are given in Table 3 and Figure 2. The majority
of stations were dominated by a polychaete assemblage. Nearshore stations PA001,
PA003, PA004 and PA005 were dominated by a amphipod assemblage, while several
scattered stations (e.g., PA032, PA040, PA062, PA090) were characterized by a mixed
polychaete/amphipod/mollusk assemblage (Figure 4).
The dominant taxon collected from the Mississippi Sound samples was the
polychaete, Mediomastus ambiseta representing 20.8% of the total individuals collected
(Table 4). Other dominant taxa included the tube-dwelling (and mat-forming) amphipod,
Cerapus benthophilus, the rhynchocoel, Tubulanus (LPIL) and the polychaetes
Paraprionospio pinnata and Streblospio benedicti representing 8.8%, 5.5%, 4.8% and
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4.1% of the total assemblage, respectively. The polychaete, M. ambiseta was the most
widely distributed taxon being found at 88% of the stations (Table 4). The distribution of
dominant taxa representing > 10% of the total assemblage at each station is given in
Table 5.
Station taxa richness and station density data are given in Table 6 and Figures 5
and 6. Taxa richness varied considerably and ranged from a single polychaete taxon at
Station PA049 to 25 at Station PA039 (Table 6; Figure 5). There were no significant
statistical correlations between taxa richness and either sediment %TOC, sediment %sand
or sediment %silt+clay. Station densities also exhibited considerable variation ranging
from 43 organisms/m2 at Station PA049 to 9957 organisms/m2 at Station PA003 (Table
6; Figure 6). There were no significant statistical correlations between station density and
either sediment %TOC, sediment %sand or sediment %silt+clay.
Taxa diversity and evenness are given in Table 6 and Figures 7 and 8. Taxa
diversity (H’) ranged from 0 at Station PA049 (only a single taxon present) to 2.92 at
Station PA081 (Table 6; Figure 7). Taxa evenness (J’) ranged from 0 at Station PA049 to
1.00 at numerous stations (Table 6; Figure 8).
The results of the hierarchical cluster analysis are given in Figure 9. The 100
stations clustered into a myriad of station groupings. These station grouping provided
little biological discrimination based on species composition due in part to the lack of
replication, but primarily due the variation seen in taxa distribution and abundance
between stations.
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HISTORIC COMPARISONS
The Mississippi Sound and adjacent waters were sampled in 1980-81 by BVA as
part of a Corps of Engineers program to develop a dredging management plan for
Mississippi Sound (U.S. Army Corps of Engineers 1982). Twelve stations sampled in
2005 were identical to stations sampled in the Fall of 1980 (Table 7). The stations
sampled in 1980 were divided into several general habitat types based on water depth and
sediment composition. The 12 stations sampled in 1980 which were resampled in 2005
were categorized as either clean sand (tidal pass/shallow sound), shallow (coastal margin)
mud or deep (open sound) muddy sand (Table 7). Only two station pairs from 1980-2005
have similar sediment composition (38/094 and 36/098) – in most instances there has
been a major shift in sediment texture – in the majority of station pairs there has been an
increase in the sediment %sand (Table 7). There has been a dramatic decrease in both
taxa richness and macroinvertebrate density at all station pairs from 1980 to 2005. The
changes in sediment composition have also led to a change in dominant taxa between
1980 and 2005 (Table 7). These changes in assemblage composition have generally
resulted in a shift from a diverse, mixed assemblage of polychaetes, mollusks and
amphipods to one dominated by one or several opportunistic polychaete taxa (e.g.
Mediomastus ambiseta, Paraprionospio pinnata). These data are reflective of the
typically dynamic nature of the benthic communities in shallow coastal areas of the Gulf
of Mexico. The assemblages in the Singing River Island area and in Mississippi Sound
exhibit the influences of annual variation in riverine inputs and the effects of numerous
hurricanes which have impacted the northern Gulf in the past 25 years.
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LITERATURE CITED
Clarke, K.R. and R.N. Gorley. 2003. PRIMER 5 (Plymouth Routines in Multivariate
Ecological Research). Plymouth Marine Laboratory, Plymouth, United Kingdom.
Pielou, E.C. 1966. The measurement of diversity in different types of biological
collections. Journal of Theoretical Biology 13:131-144.
U.S. Army Corps of Engineers, Mobile District. 1982. Benthic Macroinfauna community
characterizations in Mississippi Sound and Adjacent Waters. Final Report. 442
pp.
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