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COMPARISON OF CARBON AND NITROGEN FLUXES IN TIDEFLAT FOOD WEBS DOMINATED BY BURROWING SHRIMP OR BY CULTURED OYSTERS
Citation:
DeWitt, T H. AND P M. Eldridge. COMPARISON OF CARBON AND NITROGEN FLUXES IN TIDEFLAT FOOD WEBS DOMINATED BY BURROWING SHRIMP OR BY CULTURED OYSTERS. Presented at Pacific Estuarine Research Society meeting, Tacoma, WA, May 18-19, 2001.
Description:
Two species of indigenous, thalassinid burrowing shrimps are pests to the benthic culture of Pacific oysters (Crassostrea gigas) because deposition of sediment excavated by the shrimps buries or smothers the oysters. Carbaryl pesticide is used to reduce burrowing shrimp densities on commercial oyster beds in Willapa Bay and Grays Harbor (Washington). Many direct impacts of carbaryl and oyster culture on the shrimp, other estuarine benthic invertebrates, and fishes have been characterized. However, trade-offs in ecosystem functions between burrowing shrimp-dominated tideflats and oyster-dominated tideflats have not been investigated. We used a series of models to examine how shrimp- or oyster-dominated tideflats affect the structure and dynamics of tideflat food webs, and to examine how food web structure affects the flux of carbon and nitrogen between the tideflat and overlying water column. The food web model was constructed using existing benthic community structure data from intertidal commercial oyster beds and un-farmed tideflats dominated by the mud shrimp, Upogebia pugettensis. Scenarios of changes in benthic community structure preceding and following the application of carbaryl were constructed using existing data from environmental impact studies and ecological research on burrowing shrimp. Community structure data from each scenario were used to parameterize separate food web models. Inverse analysis of the food web models from the suite of scenarios produced a projection of changes of within-tideflat fluxes of carbon and nitrogen associated with various stages of oyster farming. Two predictions generated by this analysis are that 1) Upogebia-dominated tideflats may have greater rates of flux of carbon and nitrogen between the benthos and water column than oyster-dominated tideflats, and 2) Upogebia-dominated tideflats may sustain greater rates of in-situ primary production than oyster-dominated tideflats. Studies are underway to validate these models, and future work is envisioned to test predictions generated by the models.