Carbon Inputs to Bivalve Mollusks: A Comparison of Two Estuaries

Abstract

Corresponding trends in δ 13 C values for particulate organic carbon (POC) and the tissues of several filter-feeding bivalve mollusks in the Sheepscot estuary, Maine, indicate assimilation of terrestrial organic matter by these estuarine organisms. An adjacent estuary, the Damariscotta, of similar morphology but receiving little river input shows no such isotope change in either POC or bivalves, but rather a domination by marine isotopic values. Geographically localized or species-specific departures from these trends appear to be related to two mechanisms: (1) the influence of locally abundant, isotopically distinct, aquatic macrophytes in an area of seasonally low flushing; (2) surface-deposit feeding on benthic microalgae with anomolously high δ 13 C values.Key words: δ 13 C, Mytilus edulis, Mya arenaria, Macoma balthica, POC, estuarine comparisons, bivalve feeding