Stability and Trophic Structure in Deposit-Feeding and Suspension-Feeding Communities

Suspension-feeding benthic marine organisms feed by straining particles from the overlying water. Deposit feeders feed by ingesting bottom sediments. These two alternative strategies bring about many differences in food predictability, interspecies interactions, and population dynamics. Because suspension feeders rely principally upon phytoplankton for food, they are subject to a very unpredictable energy source. This results in few permanent sets of species associations due to competitive interactions, great fluctuations in population size, and patchy distributions. Deposit feeders that rely upon great amounts of water-borne detritus are subject to the same lack of predictability. However, where the rate of sedimentation of organic detritus is not so high, the food source for deposit feeders is much more predictable. This is because bacteria provide the rate-controlling step for the generation of food, and organic matter resides in the bottom as a "sink," buffering benthic deposit-feeders against fluctuations in abundance of organic matter in the overlying water. In addition, the presence of deposit-feeding food within the substratum allows different species to interact and outcompete other species, due to their greater efficiency at exploitation. The mobility of deposit feeders also permits competitive interference to result in exclusion. Thus, species structures that are due to competitive interactions should be important in deposit-feeding communities and unimportant in suspension-feeding communities. These remarks apply only to the trophic dimensions of the niche. Interference mechanisms, for example, may be very important in the distribution of epifaunal suspension feeders where the niche dimensions of space are considered (as in rocky intertidal surfaces).