Influence of freshwater inflow on the habitat value of oyster reefs in Southwest Florida estuaries

When assessing oyster-reef habitat in estuaries it is important to understand the influence of salinity on the spatial and temporal variability of associated organisms. How comparable is community structure among stations located at different points along the salinity gradients of estuaries or among tidal tributaries that experience different levels of freshwater inflow? Do assemblages vary seasonally in response to changing salinity and freshwater inflow? To address these questions, multivariate techniques were employed to analyze decapod crustacean and fish abundance data. Organisms were collected at three reefs along the salinity gradient of three estuaries: the Caloosahatchee River and estuary, Estero River and Bay, and Faka Union Canal and Bay. Additional collections were made from reefs located near the mouths of Estero Bay’s five tidal tributaries.

Samples were dominated by the decapods Eurypanopeus depressus and Petrolisthes armatus. Commonly occurring species included the decapods Panopeus obesus, Alpheus heterochaelis and Rhithropanopeus harrisii and the fishes Gobiosoma robustum, Lophogobius cyprinoides and Gobiesox strumosus. Analysis of similarities suggested differences among stations located along the salinity gradients of all three estuaries. Community structure also varied among stations located near the mouths of the tidal tributaries of Estero Bay. Multidimensional scaling identified community structure present at upper stations as distinct from that downstream and at high-flow tributaries as distinct from that near low-flow tributaries. Upper stations and stations near high-flow tributaries were typified by E. depressus and gobiid fishes. Downstream stations and stations near low-flow tributaries were typified by E. depressus and P. armatus. Percent dissimilarity was greatest when upper and lower stations were compared along the salinity gradient or when low salinity and high-salinity sites were compared among tributaries. Within-station sample variability tended to be higher upstream or in association with high-flow tributaries. 

Additional Readings:
Van Horn, J & SG Tolley. In press. Seasonal patterns of distribution along a salinity gradient in the flatback mud crab Eurypanopeus depressus. Gulf of Mexico Science

Tolley, SG, AK Volety, M Savarese, L Walls, C Linardich & EM Everham III. 2006. Impacts of salinity and freshwater inflow on oyster-reef communities in Southwest Florida. Aquatic Living Resources 19:371-387

Tolley, SG, JT Winstead, L Haynes & AK Volety. 2006. Influence of salinity on the prevalence of the parasite Loxothylacus panopaei in the xanthid Panopeus obesus in Southwest Florida. Diseases of Aquatic Organisms 70: 243-250

Tolley, SG & AK Volety. 2005. The role of oysters in habitat use of oyster reefs by resident fishes and decapod crustaceans. Journal of Shellfish Research 24:1007-1012

Tolley, SG, AK Volety & M Savarese. 2005. Influence of salinity on habitat use of oyster reefs in three Southwest Florida Estuaries. Journal of Shellfish Research 24:127-138

Tolley, SG, AK Volety & M Savarese. 2003. Shellfish research and adaptive resource management in Southwest Florida: oysters as sentinels of ecosystem health. World Aquaculture 34:64-66

This project was funded by the South Florida Water Management District and by a Congressional Grant awarded through the U.S. Environmental Protection Agency. In addition, many of the student interns involved in the project were supported by a Congressional Grant from the U.S. Department of Education.