ORGANIC AGGREGATES IN DETRITAL FOOD WEBS - INCORPORATION BY BAY SCALLOPS ARGOPECTEN IRRADIANS

Bay scallops Argopecten irradians were fed organic aggregates produced from the dissolved organic material (DOM) released from 5 species of marine macrophytes (Fucus vesiculosis, Ulva lactuca, Gracilaria tikvahiae, Spartina alterniflora, Zostera marina). The detrital food web pathway from macrophytes to scallops via aggregates was traced with N-15 and compared with nitrogen incorporation via direct absorption of DOM or consumption of morphous detrital particles, which are fragments of the original material. All 3 sources of N were fed to scallops for 4 to 24 h in a laboratory flow-through system. In all cases, scallops incorporated little or no nitrogen when fed DOM or morphous detritus (less than or equal to mu g(-1) dry wt h(-1)), but ranged from 56 to 133 mu g N g(-1) dry wt h(-1) when fed aggregates. Nitrogen uptake was linearly related to the amount of time scallops were fed aggregates (r(2) = 0.87), regardless of the macrophyte source of the DOM. We interpret these data to suggest that labile DOM from any source can potentially be incorporated by metazoan consumers via the aggregate pathway.