INCORPORATION OF ORGANIC AGGREGATES BY MARINE MUSSELS

Two marine mussels, Geukensia demissa (Dillwyn) and Mytilus edulis (L. ) collected in 1990 in Old Silver Beach, Falmouth, Massachusetts, inco rporated nitrogen when fed N-15-labelled organic aggregates produced f rom dissolved organic nitrogen released by the brown seaweed Fucus ves iculosis. Uptake of N-15 On the aggregate diet was linear over the cou rse of 24 h, and unincorporated N-15 was eliminated from the gut after 48 h. Both species of mussels incorporated approximately five times m ore N when they were fed organic aggregates than when they were fed ei ther N-15-labelled dissolved organic material (DOM) or particulate det ritus, both of which were also derived from the seaweed. Nitrogen upta ke was greatest in controls fed the diatom Thalassiosira weissflogii; mussels fed phytoplankton incorporated seven times more nitrogen than those fed aggregates. However, aggregates could supply an estimated 7 to 14% of the N requirements for both mussels, whereas DOM or particul ate detritus could only supply 1 to 3%. These data provide evidence th at, a food web pathway exists from primary producer to released dissol ved organic nitrogen to microbial organic aggregate to metazoan consum er, and, further, that it can be more important in a detrital food web than either particulate detritus or DOM.