Phytoplankton-based production of the clam Corbicula japonica in a low-turbidity temperate estuary as identified by fatty acid biomarkers and stable isotopes.

Abstract

The Asian brackish water clam, Corbicula japonica, is an infaunal filter feeder in the soft bottom the of estuary, and plays an important role in the functioning of the estuarine ecosystem. Stable isotope signatures and fatty acid biomarkers were determined to identify dietary sources of C. japonica in the low-turbidity temperate Seomjin River estuary of Korea. The present study addresses the patterns of its resource utilization as relating to clam size, sites (salinity gradient), and seasons (pre- and post-monsoon). Both δ13C and δ15N in the clam tissues overlapped with those of riverine and estuarine suspended particulate organic matter (R- and E-SPOM), with no apparent effects of size, site, and season on their absolute values. Biogeochemical proxies seemed to be useful to identify the contribution of autochthonous phytoplankton production to the E-SPOM pool. The high content of essential polyunsaturated fatty acids in the E-SPOM supported that phytoplankton might be an important contributor to the E-SPOM pool. Close FA profiles between C. japonica and E-SPOM revealed that while the clam production is largely dependent upon phytoplankton-derived organic matter irrespective of site and season in the unique low-turbidity estuarine condition, riverine terrestrial particulate matter plays only a minor role in their nutrition. Our findings suggest that the low quantity of riverine particulate matter and in situ primary production due to water turbidity play a crucial role in determining regional heterogeneity of the trophic base of an estuarine food web.