CONTRIBUTION OF MARINE-DERIVED ORGANIC-MATTER TO AN ATLANTIC COAST, FRESH-WATER, TIDAL STREAM BY ANADROMOUS CLUPEID FISHES

This study used stable isotope analysis to evaluate the hypothesis tha t upstream migrations by anadromous clupeid (Alosa spp.) fishes repres ent an ecologically important seasonal subsidy to annual energy and nu trient budgets for coastal waters of the Atlantic slope. Dual stable i sotope ratio analyses (delta(31)C and delta(15)N, parts per thousand) were conducted on >200 samples representing major ecological component s of Wards Creek, Virginia, and temporal trends in the stable isotope signatures of these components were related to the timing of Alosa-der ived allochthonous inputs. Carbon ratios (delta(13)C) for migratory (o ceanic) Alosa spp. arriving in Wards Creek were enriched by 10.2 parts per thousand compared to ratios for resident fishes. The timing and m agnitude of shifts in the delta(13)C values of documented Alosa predat ors suggest that predators in Wards Creek derive a substantial proport ion of their biomass carbon from marine sources during the Alosa spawn ing run. The unique trophic structure of Wards Creek may be related to ecological linkages between tidal fresh waters and coastal marine sys tems and the greater taxonomic complexity of tidal freshwater faunal a ssemblages compared to other aquatic systems.