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The Relationship of Seagrass-Associated Fish and Crustacean Communities to Habitat Gradients in Florida Bay

By R.E. Matheson1, David Camp1, Mike Robblee2, Gordon Thayer3, Dave Meyer3, and Lawrence Rozas4

1FWC, Florida Marine Research Institute, St. Petersburg, FL., USA
2U.S. Geological Survey, Center for Water and Restoration Studies, Miami, FL., USA
3NOAA, NCCOS, Center for Coastal Fisheries and Habitat Research, Beaufort, NC., USA
4NOAA Fisheries, Estuarine Habitats and Coastal Fisheries Center, Lafayette, LA., USA

Restoration of the Greater Everglades ecosystem will be multifaceted, but a large component of the program involves reestablishing a more natural hydrological regime. Downstream of the Everglades, changes in the quantity, timing, and distribution of freshwater flows entering Florida Bay will affect the resident biota. This project was designed to provide baseline data for one important faunal component of the Florida Bay ecosystem: seagrass-associated fish, caridean and penaeid shrimp, and portunid crabs. Seagrass beds are one of the most spatially extensive and important habitats in Florida Bay, and the extent, composition, and health of seagrass beds can definitely be affected by changes in freshwater inflow. Seagrass-associated faunal communities can be affected directly by salinity changes or indirectly by changes in the seagrass habitat. This study provides baseline data needed by managers to create models that can predict what will happen as a result of changes in freshwater delivery to Florida Bay and to evaluate the success of upstream restoration activities.

We used 1-m2 throw-traps to collect seagrass-associated fauna at 18 sites distributed throughout Florida Bay. For analytical purposes, our sites can be grouped geographically (fig. 1): 1) northeast--Black Betsy, Bob, Butternut, Deer, Eagle, and Nest Keys; 2) interior--Bob Allen, Buttonwood, Crab, Roscoe, Spy, and Whipray Keys; and 3) peripheral--Barnes, Joe Kemp, Johnson, Palm, Rabbit, and Sandy Keys. Three habitats (bank, basin, and near-key) were sampled at each site during wet (October) and dry seasons (April-May) from 1998 through 2000, yielding 360 bank samples, 360 basin samples, and 270 near-key samples. We identified 7,539 fish and 62,786 shrimp and crabs from these samples.

A gradient was apparent in both habitat features and biotic communities across the three regions (table 1). Northeastern sites had lower, more variable salinities; shallower sediments; less seagrass cover; and lower diversity and abundance of fish and crustaceans. Levels of these same parameters were often intermediate at interior sites and highest at peripheral sites.

The abundance patterns of the five dominant fish species were less consistent with this gradient than were the abundance patterns of the five dominant crustacean species. The abundance of only one fish species, Lucania parva, strictly followed the gradient of northeast<interior<periphery, and two fish species, Floridichthys carpio and Opsanus beta, were found at similar abundances in all three regions. Anchoa mitchilli and the sixth-ranked species, Microgobius gulosus, were both most abundant at northeastern and interior sites; both of these species are often found in the low-salinity portions of estuaries and are weakly associated (if at all) with seagrass. Among crustaceans, abundances of the top five species were all low in the northeast, moderate or high in the interior, and high on the periphery of the bay. The strongest apparent relation between abundance and salinity were observed for Farfantepenaeus duorarum and Gobiosoma robustum. Both of these species were essentially absent at salinities below 29 ppt but were among the most abundant species at higher salinities. Greater seagrass-bed development (i.e., greater density, leaf area, or diversity) was often accompanied by greater abundances of several species, including F. duorarum, G. robustum, Thor floridanus, and O. beta.

Table 1. Characterization of habitats and faunal communities in three regions within Florida Bay. Seagrass diversity is determined by the relative contribution of each of the species collected during this study to the overall abundance of seagrass in each region. Only the five most abundant fish and five most abundant crustacean species are included.
Parameter
Northeast
Interior
Periphery
Salinity low high high
Salinity CV high low low
Sediment Depth low moderate high
Seagrass Shoots low moderate high
Seagrass Biomass low moderate high
Seagrass Diversity low moderate high
Seagrass Canopy Height low moderate high
Fish Abundance low moderate high
Number of Fish Species low low high
Lucania parva low moderate high
Gobiosoma robustum low high moderate
Floridichthys carpio moderate moderate moderate
Opsanus beta moderate moderate moderate
Anchoa mitchilli high high low
Crustacean Abundance low moderate high
Number of Crustacean Species low moderate high
Thor floridanus low high high
Hippolyte zostericola low moderate high
Farfantepenaeus duorarum low moderate high
Alpheus heterochaelis low high high
Periclimenes americanus low moderate high

Alterations in the pattern of freshwater inflow could affect most of the physical and biotic patterns which we observed in Florida Bay. The effects of these alterations on fauna will be species-specific. Our study provides data for predicting these changes prior to restoration and for documenting these changes after restoration.

Contact: R.E. Matheson, Florida Fish and Wildlife Conservation Commission, Florida Marine Research Institute, 100 8th Avenue SE, St. Petersburg, FL 33701, Phone: (727)896-8626, Fax: (727)8230166, eddie.matheson@fwc.state.fl.us


(This abstract was taken from the Greater Everglades Ecosystem Restoration (GEER) Open File Report 03-54)

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