FINAL REPORT 

February, 2004 

Quantitative assessment of benthic food 

resources for juvenile Gulf sturgeon, 

Acipenser oxyrinchus desotoi in the 

Suwannee River estuary, Florida, USA. 

Prepared by: 

R. Allen Brooks (Principal Investigator) 

Project Supervisor: 

Kenneth Sulak 

Coastal Ecology & Conservation Research Group 

USGS Florida Integrated Science Center 

Center for Aquatic Resource Studies 

7920 NW 71st St., Gainesville, FL, 32953 

U.S. Department of the Interior 

U.S. Geological Survey 

Coastal Ecology & Conservation Research Group 

Investigation Report CEC 2004-02 
U.S. Geological Survey 

Eastern Region 

Florida Integrated Science Center

QUANTITATIVE ASSESSMENT OF BENTHIC FOOD RESOURCES

FOR JUVENILE GULF STURGEON, ACIPENSER OXYRINCHUS 

DESOTOI, IN THE SUWANNEE RIVER ESTUARY, FLORIDA, USA. 

Final Report 

16 February 2004 

Prepared by: 

R. Allen Brooks* and Kenneth J. Sulak

USGS Florida Integrated Science Center, Center for Aquatic Resource 

Studies, 

7920 NW 71st St., Gainesville, FL, 32653, 352-378-8181 

Collaborators:

Kenneth Litzenberger, U.S. Fish and Wildlife Service, Lower Suwannee 

National Wildlife Refuge

*phone: (352) 378-8181 ext. 3478, email: allen_brooks@usgs.gov
Figure Legends 

Figure 1. The Suwannee River, Florida, with a circle inset which encloses the estuarine 

river mouth area (rkm 0-2.5) utilized as trophic habitat by juvenile Gulf sturgeon. 

Figure 2. Five different sectors of the Suwannee River Estuary based upon salinity regimes. 

Figure 3. The location of the random sampling sites used in this study. The triangles indicate 

June-July, 2002, samples (n=156) and the circles indicate February-April, 2003, samples 

(n=103). 

Figure 4. A) Comparative mean abundance (number of individuals/m2

 ± 95% C.I.) of 

benthic macrofauna (> 0.5 mm) from core samples in the Suwannee River estuary. B) 

Comparative mean biomass (g dry wt./m2

 ±s.e.) of benthic macrofauna (> 0.5 mm) from 

core samples in the Suwannee River estuary. Location abbreviations are as follows: WDP – 

Wadley Pass, EP – East Pass, NS – North Sound, SS – South Sound, and WP – West Pass. 

Figure 5. Interpolated map of macrofaunal density (number of individuals/m2

) in the 

Suwannee River estuary during the summer of 2002 (A) and winter of 2003 (B). 

Figure 6. Interpolated map of benthic biomass (g dry wt./m2

) of benthic macrofauna in the 

Suwannee River estuary during the summer of 2002 (A) and winter of 2003 (B). 

Figure 7. Relative composition of benthic macrofaunal taxa from core samples in the 

Suwannee River estuary. 

Figure 8. Interpolated map of amphipod density (number of individuals/m2

) in the 

Suwannee River estuary during the summer of 2002 (A) and winter of 2003 (B). 

 

Figure 9. Interpolated map of polychaete density (number of individuals/m2

) in the 

Suwannee River estuary during the summer of 2002 (A) and winter of 2003 (B). 

Figure 10. Interpolated map of brachiopod density (number of individuals/m2

) in the 

Suwannee River estuary during the summer of 2002 (A) and winter of 2003 (B). 

Figure 11. Interpolated map of the density (number of individuals/m2

) of macrofauna which 

fall into the Principal Foods category in the Suwannee River estuary during the summer of 

2002 (A) and winter of 2003 (B). 

Figure 12. Interpolated map of the Biased Food Density (number of individuals/m2

) estimate 

based upon core samples taken in the Suwannee River estuary during the summer of 2002 

(A) and winter of 2003 (B). 

Figure 13. Interpolated map of the Adjusted Food (g dry wt./m2

) estimate based upon core 

samples taken in the Suwannee River estuary during the summer of 2002 (A) and winter of 

2003 (B). 
Figure 14. The location of the places within the Suwannee River Estuary that juvenile (,1 m) 

Gulf sturgeon and the number which have been caught, USGS sampling 1988-1995. 
 

Abstract 

 Gulf sturgeon, Acipenser oxyrinchus desotoi, forage extensively in the Suwannee 

River estuary following emigration out of the Suwannee River. While in the estuary, 

juvenile sturgeon primarily feed on benthic infauna. In June-July, 2002, and Feb-April, 

2003, random sites within the estuary were sampled for benthic macrofauna (2002, 

n=156; 2003, n=103). A mean abundance of 2,562 individuals/m2 (s.e. + 204) was found 

in the summer, with significantly reduced macrofaunal abundance in the winter (mean 

density of 1,044 individuals/m2

, s.e. + 117). Benthic biomass was significantly higher in 

the summer with an average summer sample dry wt. of 5.92 (s.e. + 0.82) g/m2 compared

to 3.91 (s.e. + 0.67) g/m2

 in the winter. Amphipods and polychaetes were the dominant 

taxa collected during both sampling periods. A Principal Food estimate indicated that the 

potential food resource value for juvenile Gulf sturgeon is spatially heterogeneous within 

the Suwannee River estuary. 

Introduction

The Gulf sturgeon, Acipenser oxyrinchus desotoi, was designated as threatened by 

the U.S. Fish and Wildlife Service in 1991, under the U.S. Endangered Species Act of

1991. Subsequently, there has been a need to acquire information related to locating and 

characterizing their critical habitats (USFWS and Gulf States Marine Fisheries 

Commission, 1995). The largest population of Gulf Sturgeon utilizes the Suwannee

River, Florida, and estuary (Sulak & Clugston, 1998). Prior to spring spawning, sturgeon 

from offshore begin pre-migratory staging around mid-February with movement into the 

lower river from the estuary. After spawning up-river in March-April, Gulf sturgeon 

reside in the river, fasting until October-November (Mason & Clugston 1993). When they

emigrate back to the estuary, Gulf sturgeon begin active foraging to replace lost energy 

reserves. Sturgeon over the age of five/six spend the winter beyond the estuary, but 

juveniles remain and feed in the estuary during the winter (Fox & Hightower, 1998;

Sulak & Clugston, 1998). Recent analysis indicates that some juveniles age 1-6 remain 

and feed in the estuary year round (USGS 17 year Suwannee River Gulf Sturgeon 

Database). 

1

 Three passes (inlets), two with previously dredged navigation channels 

exist within the mouth of the Suwannee River. None of the channels are currently 

maintained for navigation all have become sediment-filled over time. The U.S. Army

Corps of Engineers (USACE) has proposed to dredge one inlet, Wadley Pass, in an area 

probably used as feeding habitat by juvenile sturgeon (F&W Coordination Act Report: 

GEC, 2002). The channel is planned to be approximately 25 m wide by 3 m deep 

extending for approximately 2.5 miles (Figure 1). It has been proposed that the dredge

material be placed subtidally adjacent to Cat, Little Bradford, and No-Name Island to aid

in shoreline stabilization (F&W Coordination Act Report: GEC, 2002). Of concern is 

how maintenance dredging and/or spoil disposal will impact the threatened and

endangered species which are known to inhabit the Suwannee Estuary (e.g., West Indian 

Manatee, Gulf sturgeon). 

 

Juvenile sturgeon have been found to consume primarily benthic infauna while in 

the estuary (Huff, 1975; Mason & Clugston 1993). Thus, any alterations within the 

estuary that changes either sediment grain size/sorting or chemistry may impact juvenile 

food resources (Kenny & Rees, 1996; Seiderer & Newell, 1999). In order to prevent 

disruption of sturgeon migration patterns, the date of dredging has been restricted to 

between May 15th and October 15th while the majority of the sturgeon are still upriver.

However, benthic macrofauna recovery from dredging may require a longer time frame

(De Grave & Whitaker, 1999) limiting available food resources for juvenile Gulf 

sturgeon within the estuary. 

 Gulf sturgeon feed only in the marine environment (Mason & Clugston, 1993; Gu et 

al., 2001), with adults and juveniles foraging extensively in the estuary during winter 

(November to February-March) (Mason & Clugston 1993). Therefore, it is imperative to 

acquire food resource information for this critical area. Analysis of the current benthos 

status will allow for informed management of future actions in the estuary, and can be

used to minimize impact to sturgeon trophic habitat. Most environmental impact studies 

do not have a pre-impact baseline and rely upon what appear to be relatively similar sites 

to represent “control areas”. This study allowed acquisition of quantitative “before”

samples which can be used to comparatively evaluate post-dredging changes. Two 

objectives regarding macroinfauna within the Suwannee River Estuary are addressed in 

this study: 1) Determination of the spatial distribution, abundance, and biomass of 

potential food resources for juvenile Gulf sturgeon. 2) Evaluation of quantitative methods 

for predicting which estuarine areas are potentially most important in providing food 

resources for juvenile sturgeon. 

Methods 

A) Study Area 

 The Suwannee River is one of Florida’s largest rivers and has an average flow of 

299.6 m3

 s-1 (Mattson, 1992) (Figure 1). The river is not dammed, and the mouth of the 

river receives a substantial freshwater plume (Mattson, 1992; Mason et al., 1994). The

Suwannee River Estuary is separated from the Gulf of Mexico by a series of oyster reefs. 

It can be divided up into five sectors differing in salinity (Figure 2). The river has three 

main exits into the Gulf of Mexico – West Pass and East Pass that are natural passes, and 

Wadley Pass which is man made. West Pass receives the main outflow of freshwater. The 

estuarine sound can be separated into two parts, North and South Sound. The South 

Sound receives substantial freshwater input directly from West Pass. However, the North 

Sound generally does not receive as much same freshwater input and usually maintains 

more saline conditions. We hypothesized that the five sectors of the estuary, Wadley 

Pass, West Pass, East Pass, North Sound, and South Sound, would differ in benthic 

community parameters based upon salinity and freshwater input (Kimmerer, 2002). 

B) Benthos Sampling 

2

 A virtual grid of 100 m x 100 m cells was projected over the entire Suwannee Estuary. 

 

In June-July, 2002 156 random sites and in Feb-April, 2003 103 random sites, were 

selected for sampling (Figure 3). Random sites were allocated equally among the five 

different sectors of the estuary (treated as five strata) discussed above and located in the 

field using a Garmin GPSMAP 76S. At each sampling site, a benthic core was taken to

sample macrofauna (> 0.5mm in size). The core taken was 15 cm in diameter and 15 cm

deep. Each core sample was sieved through a 0.5 mm mesh in the field. For each sample 

subsurface salinity (0.5 m depth), water temperature, dissolved oxygen content, and pH 

were measured using a YSI 6000 handheld multimeter. Upon return to the laboratory, all 

macrofauna were identified to lowest possible taxon. Dry weight (to the nearest 0.001 g) 

of each sample was determined after drying for 24 hours at 60° C. All bivalve and 

gastropod shell material was discarded prior to dry weight determination. Polychaetes 

were identified by specialists at the Atlantic Reference Centre of the Huntsman Marine 

Science Centre, St. Andrews, New Brunswick, Canada. Amphipods were identified 

according to Bousfield (1973). 

 

Statistical Analysis 

A) Fauna Abundance and Distribution 

Due to a lack of normality and homogeneity of variances among the data, all data 

were compared using nonparametric statistical comparison techniques. Mann-Whitney 

Rank Sum Test was used to test for significant differences in macrofaunal density and 

biomass based upon season, summer (July) versus winter (February-March). The summer 

and winter sampling intervals also corresponded to dry (low flow) versus wet (high flow)

times of the year, respectively. Kruskal-Wallis ANOVA on Ranks comparisons was used 

to test for significant differences in macrofaunal density, macrofaunal biomass, amphipod 

density, and polychaete density among the five estuarine sectors (Figure 2) for each 

season separately. If Kruskal-Wallis results indicated a significant treatment effect, 

Dunn’s Method multiple comparison tests were subsequently performed to determine

significant differences (Glantz, 1997). 

 The point values (i.e., macrofauna density, macrofauna biomass, amphipod density) 

for each sample were used to create interpolated maps of the study area, using an Inverse 

Distance Weighting (IDW) method in the Spatial Analyst extension of ArcView 3.2. An 

edit mask was used to exclude all land cover and constrain the interpolation to only the 

sampled area. IDW is an interpolation technique in which estimates are made based on 

values at nearby locations weighted only by distance from the interpolation location. 

IDW does not make assumptions about spatial relationships except the basic assumption

that nearby points are more closely related than more distant points. Twelve neighbors 

were used for the interpolation (power of two and cell size of 100 m). 

 

B) Principal Foods Analysis 

3

 Two studies have examined gut contents of juvenile Gulf sturgeon. Huff (1975) found 

that guts of juveniles in the Suwannee River Estuary feed upon non-tube building 

amphipods, isopods, insect larvae and mud shrimps. Mason & Clugston (1993) found 

similar prey in juvenile Gulf sturgeon gut contents, including non-tube building 

 

crustaceans and insect larvae, with relatively few organisms that possess either a hard

carapace or shell. Heard et al. (2002), did not examine gut contents, but stated that 

juvenile Gulf sturgeon consume non-tube building amphipods. After review of these 

studies, three different principal food categories (Principal, Secondary, and Minor) were 

established (Table 1). 

 Using these three food categories, three ways to predict potential food resources for 

juvenile Gulf sturgeon were examined: 

1) Principal Food Density – This estimate is simply the density (individuals/m2

) 

of macrofauna which fall into the Principal Foods category. Using only the density of 

Principal Food items, however, ignores the Secondary and Minor Food categories. 

2) Biased Food Density – The density of macrofauna (individuals/m2

) was 

weighted by food category: Biased Food Density = [(1.0*Principal Food items

/m2

)+(0.66*Secondary Food items /m

2

)+(0.33*Minor Food items/m2)]”. The Biased Food 

Density estimate does not take benthic biomass (i.e., energy) into account. 

3) Adjusted Biomass – The Adjusted Biomass estimate was derived to take food 

categories and biomass into account. First, the Biased Food Density estimate was used to 

derive a Food Index for each sample: “Food Index = Biased Density / Total Density”. 

The Food Index returns a value between 0 and 1 for each sample. Higher index values 

indicate a greater abundance of foods in the Principal Food category. The food index for 

each sample was then combined with the sample biomass (g/m2

) to derive an Adjusted 

Biomass estimate: “Adjusted Biomass = Overall Biomass* Food Index”. 

Results 

A) Faunal Abundance and Distribution 

 In the summer samples, 6,618 individuals were collected with an average of 2,562 

macrofauna/m2 (95% C.I. + 403). Macrofauna abundance was significantly (P=0.001, 

Mann-Whitney Rank Sum Test) reduced in the winter with 1,900 individuals collected 

for an average density of 1,044 macrofauna/m2 (95% C.I. + 232). Benthic biomass was

significantly higher in the summer (P=0.015, Mann-Whitney Rank Sum Test) with an 

average summer dry wt. of 5.92 (95% C.I. + 1.3) g/m2

 compared to 3.91 (95% C.I. + 1.3) 

g/m2 in the winter. 

 Macrofaunal density was not significantly different among the five estuarine sectors in 

the summer (P=0.388, ANOVA on Ranks, Figure 4a). However, from an interpolated 

map of macrofauna density, it is apparent that density is not homogenous but rather 

patches of high density exist (Figure 5a). Specifically, areas of high density can be found 

throughout Suwannee Sound and in part of the West Pass sector. A significant difference 

in macrofaunal density was found among the five sectors during the winter (P=0.001, 

ANOVA on Ranks, Figure 4a). Both the North Sound and South Sound sectors had 

significantly higher infaunal density than the East Pass sector. An interpolated map for 

the winter also shows areas of relatively high density in the Suwannee Sound (both 

sectors) and parts of the West Pass sector (Figure 5b). 

4

A significant difference in benthic biomass was found between the five different 
Table 1. Principal food categories for juvenile Gulf Sturgeon erected from the 

 macrofauna found in the Suwanee River Estuary. 

PRINCIPAL FOODS SECONDARY FOODS MINOR FOODS 

Brachiopods Anthozoans Bivalves 

Free-Living Amphipods Cumaceans Decapods 

Insect Larvae Nematodes Gastropods 

Isopods Nemerteans Ophiuroids 

Oligochaetes Ostracods 

Shrimp Polychaetes 

Tube-Building Amphipods 

Hirudinea 
Macrofauna Density

Avg. Density

m-2

0

1000

2000

3000

4000

5000

Summer 2002

Winter 2003

Macrofauna Biomass

Location

DI EP NS SS WP Overall

Avg. Dry

Wt. (g) m-2

0

2

4

6

8

10

12

14

A.

B.

 

estuarine sectors for both summer and winter samples (P=0.007 and 0.001, respectively, 

ANOVA on Ranks). In both summer and winter, biomass was significantly greater in the

North Sound sector compared to the West Pass sector (Figure 4b). Additionally, biomass 

in both the North and South Sound sector was significantly greater than that of West or 

East Pass sectors in the winter. Patches of high biomass can be found throughout both 

Suwannee Sound sectors during both sampling times and in the summer at the mouth of 

West Pass (Figures 6a,b). 

 Amphipods and polychaetes were the numerically dominant fauna collected in this 

study (Figure 7). Although ANOVA on ranks results indicate a significant difference in 

amphipod density among estuarine regions in the summer (P=0.023), results of a Dunn’s

Multiple Comparisons Test indicated no significant differences. Areas of high amphipod 

abundance in the summer can be found in both the South Sound and West Pass (Figure 

8a) which both along with the North Sound had a significantly greater amphipod density 

than East Pass in the winter (P=0.001, ANOVA on Ranks). Overall, amphipod density 

was more homogeneous throughout the study area in the winter with smaller patches of 

high amphipod density (Figure 8b). Amphipod species richness was higher in the summer

(n=10) compared to winter (n=7) (Table 2). One amphipod species, Ampelisca abdita, 

dominated in both the winter and summer accounting for 58% of all amphipods collected. 

Parahaustorius spp. (14.4% of all amphipods collected, summer and winter) was also 

commonly collected. Cerapus tubularis (15.3% of all amphipods collected, summer and 

winter) was relatively dominant in the summer samples while Gammarus mucronatus

(1.8% of all amphipods collected, summer and winter) was relatively common in the 

winter samples. 

 Polychaete density was higher in the North Sound compared to all other estuarine 

sectors in the summer (P=0.001, ANOVA on Ranks). An interpolated map of summer

polychaete density indicates a large patch of high density in the North Sound with smaller 

patches in West Pass (Figure 9a). Polychaete density in the winter was significantly 

greater in both Sound sectors compared to West Pass and significantly greater in the 

North Sound than in East Pass (P=0.001, ANOVA on Ranks). An interpolated map of 

polychaete density in the winter indicates a large area of high density in both the North 

and South Sound (Figure 9b). Melinna (cf. cristata) dominated in both the winter and 

summer accounting for 39% of all polychaete species (Table 3). Tharyx sp., Parandalia 

americana, Glycera americana, Leitoscoloplos (cf. robustus), and Aricidea philbinae 

were also relatively abundant representing 14%, 10%, 6%, 5%, and 4%, respectively, of 

all polychaetes collected in both the summer and winter combined. 

 The stalked brachiopod, Glottidia pyramidata, and isopods were also relatively 

important taxa, representing between 2-5% and 3%, respectively, of the 

macroinvertebrates collected, respectively. The stalked brachiopod is a common food 

resource for adult Suwannee River Gulf sturgeon (Harris, 2003). Brachiopods were found 

only in the outer part of Suwannee sound, with higher densities in the summer (Figures 

10a,b). 

B) Principal Foods

5

 Interpolated maps for only the Principal Foods category are shown in Figure 11a,b. 

SUMMER WINTER

Amphipods

Polychaetes

Brachiopods

Isopods

Bivalves

Oligochaetes

Nemerteans

Other

Table 2. Percent representation of amphipod taxa collected in summer, winter and overall 

 samples. 

Species 

Percent of 

Amphipods 

Collected in the 

Summer 

Percent of 

Amphipods 

Collected in the 

Winter 

Overall 

Percent of All 

Amphipods 

Collected 

Ampelisca abdita 60.5 48.5 58.9 

Cerapus tubularis 17.2 3.3 15.3 

Haustoriidae 10.5 39.1 14.4 

Ampithoe longimana 5.5 1.3 4.9 

Corophium simile 4.2 1.2 3.7 

Gammarus mucronatus 1.1 6.1 1.8 

Cymadusa compta <1.0 0 <1.0 

Melita nita <1.0 0 <1.0 

Stenothoe minuta <1.0 <1.0 <1.0 

Luecothoe spinicarpa <1.0 0 <1.0 

Table 3. Percent representation of the dominant polychaete taxa collected in summer, 

 winter, and overall samples. 

Species 

Percent of 

Polychaetes 

Collected in the 

Summer 

Percent of 

Polychaetes 

Collected in the 

Winter 

Overall 

Percent of All 

Polychaetes 

Collected 

Melinna (cristata?) 25.1 51.9 39.0 

Tharyx 17.9 9.6 13.6 

Parandalia americana 15.2 5.8 10.3 

Glycera americana 7.0 5.8 6.4 

Leitoscoloplos (robustus?) 9.0 1.6 5.2 

Aricidea philbinae <1.0 7.2 3.8 

Kinbergonuphis 6.2 <1.0 3.4 

Paraspionospio pinnata 1.9 4.6 3.3 

Websterinereis 4.6 1.8 3.2 

Anaitides mucosa 3.5 <1.0 1.8 

Malanidae 3.7 0 1.8 

Pectinaria gouldii 2.4 <1.0 1.5 

Unidentified sp. 0 2.6 1.4 

Neanthes succinea 1.2 <1.0 1.0 

Other 1.3 5.4 4.3 


 

High densities of Principal Food items are found in West Pass and the outer Sound in the 

summer. A similar pattern is found for the winter with a high density of principal food 

items throughout West Pass and in the Sound by the mouth of West Pass. 

The Biased Food Density measure indicates high summer values in West Pass and the 

near-shore area of the South Sound (Figure 12a). A few small patches of high density, are 

also observed in the outer Sound. Only a few spots stand out in the winter (Figure 12b), 

but a pattern is still present that is similar to the summer. 

 The Adjusted Food measure, which combines both density and biomass, indicated that 

the main areas of potential high food value were located in the outer Sound in both the 

summer and winter (Figures 13a & 13b). The density of brachiopods was mathematically 

driving this pattern in the summer, but the pattern persisted in the winter, when 

brachiopod abundance was reduced. 

Discussion 

 Macrofaunal abundance in the Suwannee Estuary was within the mid range found for 

other estuaries around the Gulf of Mexico. Macrofaunal densities ranged from 0-13,701 

individuals/m2

 with an average density of 1,935 (s.e. + 137) individuals/m2. Present 

estimates of benthos density in the Suwannee Estuary are higher than those found for

Mobile Bay, AL (TechCon, 1980); Neches River Estuary, TX (Harrel & Smith, 2002); 

Nueces Bay, TX (Mannino & Montagna, 1997); and Santa Rosa Sound, FL (EPA, 1975). 

But Suwannee estuary estimates are not as high as values reported for Mississippi Sound, 

MS (USACE, 1982); Tampa Bay, FL (Culter, 1995); and Rookery Bay, FL (Sheridan, 

1997). Although macrofaunal population density differences among the five estuarine 

sectors were only found for the winter sampling, the distribution of macrofauna was very 

patchy. Areas of high population density were found throughout the Sound and in part of 

West Pass, regardless of sampling season. In contrast to these results, no significant 

differences were found for macrofaunal densities among salinity regions in Nueces Bay,

TX. Seasonal differences in benthos density were also found in the Suwannee Estuary 

with abundances over two times greater in the summer compared to winter. 

 Benthic biomass (dry weight) ranged from 0-41 g/m2

with an average of 4.8 (s.e. +

0.5) g/m2. Biomass estimates were almost 50% higher in the summer than in winter. 

Patches of high biomass were found in areas of higher salinity (e.g., Suwannee Sound), 

similar to results from Nueces Bay, Texas (Mannino & Montagna, 1997). Overall, the 

range of biomass values found in the Suwannee Estuary were substantially greater than 

the range reported from Nueces Bay (<1-9.23 g/m2

). In the Suwannee estuary, average

benthic biomass was higher than above the salt wedge (RKMS 52-64, 0.5 g/m2 + 0.1) 

(Sulak et al., in press). 

6

 Amphipods were the dominant taxa in the summer with most species being tubicolous. 

The spatial distribution of amphipod density displays a clear spatial correlation between 

high density and freshwater flow. West Pass and parts of the South Sound, which 

predominantly receive the freshwater plume, contained relative hot spots of amphipod 

density compared to the rest of the study area. Amphipod distribution may not be 


 

responding solely to the low salinity regime. Sediment deposition, particulate organic

content, and/or high oxygen content as well as freshwater inflow stimulated primary and 

secondary production may also influence amphipod distribution (Mannino & Montagna, 

1997; Kimmerer, 2002). Ampelisca, by far the most common amphipod genus collected, 

are filter feeders and have been noted for their vulnerability to sediment quality. They are 

often used as indicator species for heavy metals and PAH organic compounds in 

toxicology studies (ASTM, 2003; Gomez Gesteira & Dauvin, 2000). A high density of 

ampeliscans in the Suwannee River Estuary suggests low sediment contamination levels. 

 Polychaetes were the dominant taxa collected in the winter. The spatial distribution of 

polychaetes was opposite that of amphipods. Polychaete density was highest in the North 

Sound away from the freshwater influence of the river. Tharyx, a tube building deposit 

feeder, was commonly found in both the winter and summer. Free burrowing 

Leitoscoloplos and Parandalia were typical genera collected in the summer. 

Leitoscoloplos is a deposit feeder, while Parandalia is suspected to be a carnivore.

Melinna, a tube builder and surface deposit feeder was the dominant polychaete taxon 

collected in the winter (Fauchald & Jumars, 1979). 

 Brachiopod distribution within the Suwannee Estuary is restricted to outer Sound 

areas and appears to be associated with hard substratum provided by oyster shell material. 

Brachiopods can be found in patches of high density (> 6,000 individuals m-2) in the 

summer but have reduced abundance in winter. It is unknown if juvenile sturgeon utilize 

brachiopods as an important prey item although adults utilize them heavily (Harris, 

2003). 

 Tubiculous amphipods and polychaetes, although consumed by juvenile sturgeon, do 

not appear to be principal food items based upon gut content analysis (Huff, 1975; Mason 

& Clugston, 1993). Brachiopods were included in the principal foods category for this 

analysis based upon adult gut contents (Harris, 2003), but their inclusion needs to be reevaluated as more diet information becomes available. Other than brachiopods, isopods 

and oligochaetes are also important potential food resources in the estuary. Isopod 

density is highest near the lower parts of the river passes, while oligochaetes have a 

pocket of high density in the North Sound. 

 Depending upon which quantitative measure is used to evaluate potential resource 

value for juvenile Gulf sturgeon foraging, different locations within the estuary stand out. 

When examining the distribution of only those taxa which were assigned to the Principal 

Food category, high densities are found throughout West Pass and in the South Sound by 

the mouth of West Pass. The pattern is consistent regardless of sampling date. The Biased 

Food Density measure highlights not only areas of West Pass as containing high potential 

resource value but the outer Sound areas and the near-shore area of the South Sound as 

well. In the winter, the distribution of high resource areas based upon the Biased Food 

estimate is fairly homogeneous with relatively few hot spots. Values of the Adjusted 

Food measure are highest in the outer Sound areas away from the river mouth. 

7

Interestingly, the Adjusted Food measure does not highlight West Pass as an area 

of high resource value for juvenile sturgeon and the Biased Food Density estimate is only 

high in West Pass during the summer. Historical sampling within West Pass however has 

indicated that juvenile sturgeon are consistently found within this area, as documented in 
 

the U. S. Geological Survey (USGS) Suwannee River Gulf sturgeon database (Figure 

14). Therefore, without any additional information on juvenile habitat use it appears that 

the Principal Food Density estimate is the best predictor of potential food resources for 

juvenile Gulf sturgeon. Adult sturgeon have been found to follow what appears to be a

Levy search pattern when foraging such that an initial search direction is chosen at 

random and followed linearly until a patch of prey is located, after which movements

become random within a confined area (Edwards et al., 2003). Therefore, prey density 

and prey patch size are possibly more important than prey biomass for juvenile Gulf 

sturgeon. Estimates which incorporate an indicator of biomass such as the Adjusted Food 

measure maybe more important for other benthic fishes (e.g., Spot, Croaker, Flounder) 

with alternative foraging strategies. 

 The measures calculated in this study provide a static assessment of potential food 

resources (density and biomass) that may need to be adjusted if benthic feeding fishes 

such as the Gulf sturgeon continuously feed within the same area. In this regard, we lack 

data on benthic productivity. A sector may initially have relatively high benthic resources 

before it is foraged, but recovery time is unknown. An area with a low recolonization rate 

may not be as valuable for sturgeon over the winter feeding season compared with an

area with a higher recolonization rate (i.e., populated by fast reproducing amphipods). 

Thus, there may be a trade-off between immediate and long-term resource value in a

given area. 

 The quantitative measures used in this study have identified areas which are 

potentially sensitive to disturbance by dredging and/or spoil disposal. The Principal Food 

Density estimate is high in Wadley Pass only during the summer when sturgeon 

residence within this area is potentially low. Thus, dredging Wadley Pass in either the 

winter when there is a low food density or summer would seem to present a low potential

for long-term impact on critical juvenile sturgeon trophic habitat. 

Literature Cited 

American Society for Testing and Materials (ASTM). 2003. Standard guide for 

conducting 10-day static sediment toxicity tests with marine and estuarine amphipods. 

WK632. 

Ardisson, P.L., E. Bourget. 1997. A study of the relationship between freshwater runoff 

and benthos abundance: a scale oriented approach. Estuarine Coastal and Shelf Science 

45:535-545. 

Bousfield, E.L. 1973. Shallow-water gammaridean amphipoda of New England. Cornell 

University Press, Ithaca, NY, USA. 

Culter, J.K. 1995. Benthic infauna of Tampa Bay: Summer 1993. Tampa Bay National 

Estuary Program report no 02-95. Mote Marine Laboratory Technical Report no 420. 

8

 

De Grave, S., A. Whitaker. 1999. Benthic community re-adjustment following dredging 

of a muddy-maerl matrix. Marine Pollution Bulletin 38:102-108. 

Edwards, R.E, K.J. Sulak, M.T. Randall, C.B. Grimes. 2003. Suwannee River (FL) Gulf 

sturgeon (Acipenser oxyrinchus desotoi) movements and nearshore Gulf of Mexico habitat 

determined by acoustic telemetry. Gulf of Mexico Science:59-70. 

Fox, D.A., J.E. Hightower. 1998. Gulf sturgeon estuarine and nearshore marine habitat 

use in Choctawhatchee Bay, FL. Annual Report to National Marine Fisheries Service, 

North Carolina State University, Raleigh, N.C. 29pp. 

Glantz, S. A. 1997. Primer of Biostatistics. The McGraw-Hill Companies, Inc., USA. 

Gomez-Gesteira, J.L., J.C. Dauvin. 2000. Amphipods are good bioindicators of the 

impact of oil spills on soft-bottom macrobenthic communities. Marine Pollution Bulletin 

40:1017-1027. 

Gu, B., D.M. Schell, T. Frazer, M. Hoyer, F.A. Chapman. 2001. Stable carbon isotope 

evidence for reduced feeding of Gulf of Mexico sturgeon during their prolonged river 

residence period. Estuarine, Coastal and Shelf Science 53:275-280. 

Gulf Engineers & Consultants. 2002. Suwannee River Maintenance Dredging Dixie 

County, Florida. Fish and Wildlife Coordination Act Report, Prepared for U.S. Fish &

Wildlife Service in Jacksonville. 

Harrel, R.C., S.T. Smith. 2002. Macrobenthic community structure before, during, and 

after implementation of the Clean Water Act in the Neches River estuary (Texas). 

Hydrobiologia 474:213-222. 

Harris, J.E. 2003. Distribution of Gulf of Mexico sturgeon (Acipenser oxyrinchus 

desotoi) in relation to environmental parameters and the distribution of benthic 

invertebrates in the Suwannee River Estuary, Florida. Masters Thesis, University of 

Florida, Gainesville, FL, USA. 

Hightower, J.E., K.P. Zehfuss, D.A. Fox, F.M. Parauka. 2002. Summer habitat use by 

Gulf sturgeon in the Choctawhatchee River, Florida. Journal of Applied Ichthyology 

18:595-600. 

Huff, J.A. 1975. Life history of the Gulf of Mexico sturgeon, Acipenser oxyrhynchus 

desotoi, in Suwannee River, Florida. Florida Department of Natural Resources, 

Marine Research Laboratory Publication 16. 

Kenny, A.J., H.L. Rees. 1996. The effects of marine gravel extraction on the 

macrobenthos: results 2 years post-dredging. Marine Pollution Bulletin 32:615-622. 

9

Kimmerer, W.J. 2002. Effects of freshwater flow on abundance of estuarine organisms:

physical effects or trophic linkages? Marine Ecology Progress Series 243:39-55. 
 

Mannino, A., P.A. Montagna. 1997. Small-scale spatial variation of macrobenthic 

community structure. Estuaries 20:159-173. 

Mason, W.T., J.P. Clugston. 1993. Foods of the Gulf Sturgeon in the Suwannee River, 

Florida.Transactions of the American Fisheries Society 122:378-385. 

Mason, W.T, R.A. Mattson, J.H. Epler. 1994. Benthic invertebrates and allied 

macrofauna in the Suwannee River and estuary ecosystem, Florida. Florida 

Scientist 57:141-160. 

Mason, W.T. 1991. A survey of benthic invertebrates in the Suwannee River, Florida. 

Environmental Monitoring and Assessment 16:163-187. 

Mattson, R.A. 1992. Characteristics of benthic macroinvertebrate communities of the 

Suwannee River drainage. Technical Report (Draft), Suwannee River Water Management 

District. 

Montagna, P.A., R.D. Kalke. 1992. The effect of freshwater inflow on meiofanal and 

macrofaunal populations in the Guadalupe and Nueces Estuaries, Texas. Estuaries 

15:307-326. 

Seiderer, L.J., R.C. Newell. 1999. Analysis of the relationship between sediment 

composition and benthic community structure in coastal deposits: Implications for marine

aggregate dredging. ICES Journal of Marine Science 56:757-765. 

Shaw, J. K., P.G. Johnson, R.M. Wewing, C.E. Comiskey, C.C. Brandt, T.A. Farmer. 

1982. Benthic macroinfana community characteriazation in Mississippi Sound and 

adjacent waters. Final Report. U.S. Army Engineer District, Mobile, Alabama. Contract 

No. DACW01-80-C-0427. 

Sheridan, P. 1997. Benthos of adjacent mangrove, seagrass and non-vegetated habitats 

in Rookery Bay, Florida, USA. Estuarine Coastal and Shelf Science 44:455-469. 

Stoner, A.W., C. Acevedo. 1990. The macroinfaunal community of a tropical estuarine 

lagoon. Estuaries 13:174-181. 

Sulak, K.J., Clugston, J.P. 1998. Early life history stages of the Gulf sturgeon in the 

Suwannee River, Florida. Transactions of the American Fisheries Society 127:758-771. 

Sulak, K.J., R.A. Brooks, M. Randall. Seasonal Refugia and Trophic Dormancy in Gulf 

Sturgeon: Test and Refutation of the Thermal Barrier Hypothesis 

U.S. Fish and Wildlife Service and Gulf States Marine Fisheries Commission. 1995. 

Gulf sturgeon Recovery Plan. Atlanta, GA, USA. 

10
 

11

Wakeford, A. 2001. State of Florida Conservation Plan for Gulf Sturgeon (Acipenser 

oxyrinchus desotoi). Florida Fish and Wildlife Conservation Commission, Florida Marine 

Research Institute Technical Reports (TR-8).