Competition and Predation in Marine Soft-sediment Communities

One of the major goals of community ecology is to understand how interactions among the resident organisms affect their distribution and abundance. For terrestrial and rocky intertidal communities competition and predation clearly can play pivotal roles in community organization (28, 47, 84). The importance of biological processes in organizing marine soft-sediment communities is not as well understood (86), despite the fact that marine soft-sediments are the most common habitat on earth. As 1 argue below, paradigms of co~nmunity organization based on other habitats seem to offer little insight into the structure of marine soft-sediment communities. Rather than attempting to explain the failure of such paradigms, I argue that softsediment habitats are sufficiently different from other communities that different paradigms are needed. Soft-sediment communities are unusual in the rate at which the nature of the physical environment can change. Most sedimentary particles are smaller than the resident organisms (the infauna). The activities of the infauna can dramatically change the nature of the environment over time periods of hours or days. For instance, burrowing infauna may increase the porosity and erodability of the sediment (102). Subsurface deposit-feeders may alter the