Controls of benthic marine food webs

Are benthic marine food webs controlled by predation (top-down) or resources (bottom-up)? Although both top-down and bottom-up processes operate in all ecosystems, the aquatic literature on communities has been dominated by early work done on rocky or hard substrates, which emphasizes top-down controls. Further research to assess the importance of resources on food webs of these communities is needed. Manipulative experiments in which top-down and bottom-up factors are simultaneously varied in the field should be undertaken is to adequately evaluate is relative importance of predation and resources. Our work on the benthos of Great Sippewissett Salt Marsh in Massachusetts, USA, examined the effects of both nutrient additions to increase resources, and caging to reduce predation by epibenthic fish and crabs. It illustrates the value of such field manipulations in evaluating controls on aquatic food webs.