Potential food resources in the Suwannee River Estuary for juveniles of the threatened Gulf...

Potential food resources in the Suwannee River Estuary for juveniles of the

threatened Gulf Sturgeon, Acipenser oxyrinchus desotoi.

Allen Brooks

Ken Sulak

Coastal Ecology & Conservation Research Group

U.S. Geological Survey

OBJECTIVES• Discuss the spatial distribution and

abundance of benthos in the Suwannee River Estuary.

• Discuss which areas within the estuary are potentially most important in providing food resources for juvenile Gulf Sturgeon.

Suwannee River Estuary

STUDY AREA

EAST PASS WADLEY PASSWEST PASS

NORTH SOUND SOUTH SOUND

Sample Site Selection

• A grid (100 m centers) was placed over the entire study area.

• 156 random sites were selected for sampling inJune-July 2002

SAMPLING STATIONSJune 2002

Sampling Methods

Benthic Core– 15 cm in diameter (0.018 m2) and 15 cm deep– 0.5 mm mesh sieve

Laboratory Methods- Fauna abundance- Sample dry wt. (600 - 24 hrs)

ABUNDANCE

Avg.

Den

sity

(m2 )

0

1000

2000

3000

4000

BIOMASS

EPWLP WP NS SS

OVERALL

Avg.

Dry

Wt.

(g/m

2 )

0

2

4

6

8

10

12

No Sig. Diff.

*

1000 0 1000 2000 Meters

N

EW

S

0 - 10001000 - 20002000 - 30003000 - 40004000 - 50005000 - 60006000 - 70007000 - 80008000 - 9000> 9000No Data

Benthos Density (m2)

N

EW

S

00.01 - 11 - 55 - 1010 - 2020 - 30> 30No Data

1000 0 1000 2000 Meters

BIOMASS (g/m2)

AMPHIPODSBIVALVESBRACHIOPODSISOPODSPOLYCHAETESOTHER

64.7%

15.8%

Percent Composition of Major Taxa

5.2%3.3%

3.4%

7.6%

2000 0 2000 4000 Meters

N

EW

S

01 - 500500 - 10001000 - 20002000 - 30003000- 40004000 - 50005000 - 6000> 6000No Data

Amphipod

Density (m2)

N

EW

S

00.1 - 100100 - 200200 - 300300 - 400400 - 500500 - 600600 - 700700 - 800800 - 900900 - 10001000 - 1500> 1500No Data

1000 0 1000 2000 MetersPolychaete

Density (m2)

Density of Individuals (m2)

0 10000 20000 30000 40000 50000

Santa Rosa Sound, FL

Neches River Estuary, TX

Mobile Bay, AL

Suwannee River Estuary, FL

Rookery Bay, FL

Mississippi Sound, MS

Tampa Bay, FL

How Does the Suwannee Compare?

Objective 2:

WHAT’S FOR DINNER?

Principal Foods for Juvenile Gulf Sturgeon

•Huff, 1975- Prefer non-tube building amphipods, isopods,

insectlarvae and mud shrimps

•Mason & Clugston, 1993- Prefer non-tube building crustaceans and insect

larvae- Do not prefer organisms with a hard carapace or

shell

• Heard et al., 2002- Prefer non-tube building amphipods

Food Categories based upon Gut Content Analysis

• Principal Foods:Free Living Amphipods ShrimpIsopods OligochaetesInsect Larvae Brachiopods

• Secondary Foods:Tube Dwelling Nemerteans AmphipodsPolychaetes NematodesCumaceans AnthozoansOstracods

• Minor Foods*:Ophuiroids GastropodsBivalves Decapods

* No taxa were excluded from all categories.

N

EW

S

0 - 100100 - 250250 - 500500 - 10001000 - 2500> 2500 No Data

1000 0 1000 2000 Meters

Principal Food

Density

Biased Density

Biased Density = [(1.0*Principal Food/m2)+(0.66*Secondary Food/m2)

+(0.33*Minor Food/m2)]

1000 0 1000 2000 Meters

N

EW

S

0 - 10001000 - 20002000 - 30003000 - 40004000 - 50005000 - 6000> 6000

Biased Density

Adjusted Biomass = Overall Biomass* Food Index

Food Index = Biased Density / Total Density

The goal is to include not only faunal density but an idea of energy as well.

N

EW

S

0 - 11 - 55 - 1010 - 1515 - 20> 20No Data

1000 0 1000 2000 Meters

Adjusted Biomass

Conclusions• The density of benthic macrofauna in the

Suwannee River Estuary is within the range of other estuaries around the Gulf of Mexico.

• The distribution of taxa is patchy within the estuary.

• The use of total density may not be the best method for predicting where juvenile sturgeon might be preferentially feeding.

Acknowledgements

Ken Litzenberger, Refuge ManagerLower Swuannee National Wildlife Refuge,U.S. Fish and Wildlife Service

Gerhard Pohle, Associate DirectorAtlantic Reference Centre