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