Time-courses in the retention of food material in the bivalves Potamocorbula amurensis and Macoma balthica significance to the absorption of carbon and chromium

Abstract

Time courses for ingest~on, retention and release via feces of microbial food was investigated using 2 b~valves w ~ t h d~fferent feeding strategies, Potamocorbula amurensis and Macoma balthica. The results showed 2 pathways for the uptake of food material in these clams. The first is represented by an initlal label pulse in the feces. The second pathway operates over longer time periods. Inert Cr-labeled beads were used to determine time frames for these pathways. The first pathway, involving extracellular digestion and intestinal uptake, is relatively inefficient In the digestion of bacter~al cells by P amurensis but more efficient in M. balthica. The second pathway, involving intracellular digestion withln the digestive gland of both clams, was highly efficient in absorb~ng bacterial carbon, and was responsible for most chromium uptake. Differences in the overall retention of microbial Cr and I4C relate not to gut-passage times but to the processing and release strategies of the food material by these 2 clams.