Interactive effects of nutrient additions and predation on infaunal communities

Nutrient additions represent an important anthropogenic stress on coastal e cosystems. At moderate levels, increased nutrients may lead to increased pr imary production and, possibly to increased biomass of consumers although c omplex trophic interactions may modify or mask these effects. We examined t he influence of nutrient additions and interactive effects of trophic inter actions (predation) on benthic: infaunal composition and abundances through small-scale field experiments in 2 estuaries that differed in ambient nutr ient conditions. A blocked experimental design was used that allowed an ass essment of direct nutrient effects in the presence and absence of predation by epibenthic predators as well as an assessment of the independent effect s of predation. Benthic microalgal production increased with experimental n utrient additions and was greater when infaunal abundances were lower, but there were no significant interactions between these factors. Increased abu ndances of one infaunal taxa, Laeonereis culveri, as well as the grazer fee ding guild were observed with nutrient additions and a number of taxa exhib ited higher abundances with predator exclusion, In contrast to results from freshwater systems there were no significant interactive effects between n utrient additions and predator exclusion as was predicted. The infaunal res ponses observed here emphasize the importance of both bottom-up (nutrient a ddition and primary producer driven) and top-down (predation) controls in s tructuring benthic communities. These processes may work at different spati al and temporal scales, and affect different taxa, making observation of po tential interactive effects difficult.