CONTROLS OF BENTHIC MARINE FOOD WEBS

Are benthic marine food webs controlled by predation (top-down) or res ources (bottom-up)? Although both top-down and bottom-up processes ope rate in all ecosystems, the aquatic literature on communities has been dominated by early work done on rocky or hard substrates, which empha sizes top-down controls. Further research to assess the importance of resources on food webs of these communities is needed. Manipulative ex periments in which top-down and bottom-up factors are simultaneously v aried in the field should be undertaken is to adequately evaluate is r elative 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 t o reduce predation by epibenthic fish and crabs. It illustrates the va lue of such field manipulations in evaluating controls on aquatic food webs.