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Fresh Water Inflow and Oyster Productivity in Apalachicola Bay, FL (USA)
Citation:
OCZKOWSKI, A., F. G. Lewis, S. W. Nixon, H. L. Edmiston, R. S. Robinson, AND J. P. Chanton. Fresh Water Inflow and Oyster Productivity in Apalachicola Bay, FL (USA). Estuaries and Coasts. Estuarine Research Federation, Port Republic, MD, 34(5):993-1005, (2011).
Impact/Purpose:
Apalachicola Bay is home to an extraordinarily productive oyster fishery and supplies 90% of Florida’s oysters. The success of the oyster, as well as other commercially important fish species, is attributed to the Apalachicola River, where the spatial and seasonal variability of the discharge both repels predators and provides an important food source to bay fish. However, the headwaters of the river lie in Georgia and increasing amounts of water are being withdrawn in this area to irrigate agriculture. There is great concern among Florida fishermen and decision-makers that these withdrawals may be negatively impacting the oyster fishery. Thus, our goal in this research effort was to try to document the importance of Apalachicola River nitrogen (dissolved and particulate) to the oysters. We used stable isotopes of nitrogen and carbon to trace the interactions between the river and offshore Gulf of Mexico water in the oyster tissues. Our results suggest that the relative importance of dissolved and particulate river N varies seasonally, but overall, the N signatures in oyster tissues overwhelmingly reflect the river influence. This study demonstrates the seasonal complexities that must be considered in characterizing the Apalachicola Bay food web and illustrates the dynamic differences in food sources associated with the riverine flow regime.
Description:
Apalachicola Bay lies at the mouth of the Apalachicola River, where seasonally variable freshwater inflows and shifting winds support an unusually productive and commercially important oyster fishery. While there is concern that upstream water withdrawals may impact the fishery, the importance of riverine nitrogen (N) to oyster diets is unclear. N and carbon (C) stable isotopes (δ15N, δ13C) measured in macroalgae, surface water nitrate, and surface sediments define a gradient from enriched riverine δ15N values to more depleted values in the Gulf of Mexico. In contrast, δ13C of particulate matter is depleted in the river and enriched offshore. Oyster stable isotope signatures throughout Apalachicola Bay are more complex, but are dominated by freshwater inputs and reflect the variability and hydrodynamics of the riverine inflows.