Top down vs. bottom up control of benthic community composition on an intertidal tideflat

Abstract

Nutrient enrichment and predation have been shown to have important, though sometimes conflicting, effects on intermediate trophic levels in freshwater communities. Though predation is also important in structuring marine soft-sediment benthic communities, the influence of nutrient enrichment in marine benthic systems is less well understood. We examined the interactive effects of nutrient enrichment and predator exclusion on a benthic community to assess the importance of these factors and to test the bottom-up:top-down theory of trophic control in this habitat. Predator exclusion was associated with increased numbers of surface deposit feeders but had less impact on burrowing deposit feeders. Effects of nutrient addition on abundances were observed only in treatments allowing predator access, but increased size of a benthic polychaete, Streblospio benedicti Webster, was observed in predator exclusion treatments with nutrient addition relative to other exclusion plots. However, responses to nutrient addition and predator exclusion varied between years. These results suggest that nutrient addition may be associated with effects on benthic communities, possibly through increased benthic microalgal production, but that the presence or absence of predation may alter the visible response of benthos to enrichment.