MEPS 494:29-39 (2013)  -  DOI: https://doi.org/10.3354/meps10561

ABSTRACT: Benthic invertebrates alter estuarine ecosystem function by moderating benthic microalgal production and sediment biogeochemistry. While lethal predation eliminates the effect of invertebrates, non-consumptive effects of predation through trait-mediated indirect effects on behavior may reduce prey control of ecosystem function. Using microcosms, we investigated how chemical cues from the predatory mud crab Panopeus herbstii changed prey behavior and thereby affected the ability of the grazing-deposit feeding gastropod Ilyanassa obsoleta and filter-feeding bivalve Mercenaria mercenaria to regulate benthic ecosystem function. Sediment-water column fluxes of oxygen and nutrients, microscale profiles of sediment oxygen, benthic chlorophyll a, porewater ammonium and organic matter were measured after exposure to predator effluent. Both species had significant effects on sediment processes, with higher sediment oxygen consumption and release of ammonium to the water column, and lower porewater ammonium. However, individual effects were altered in the presence of chemical cues from P. herbstii. The negative effect of M. mercenaria on porewater ammonium was diminished by 26% in predator treatments, suggesting less movement and therefore less sediment oxidation and nitrogen removal. For I. obsoleta, there was a 30% increase in microalgal biomass and a 35% decrease in sediment ammonium release in the predator treatments, possibly associated with decreased foraging activity. In these experiments, non-consumptive predator effects indirectly altered benthic biogeochemistry, benthic microalgae and nutrient fluxes. These results suggest that experiments conducted without predators may overestimate the impact of benthic fauna on ecosystem processes and that changes in community structure resulting in loss of predators may have indirect effects on benthic ecosystem function, leading to faster nitrogen turnover and release to the water column.

KEY WORDS: Trait-mediated interactions · Non-consumptive effects · Benthic invertebrates · Benthic microalgae · Sediment biogeochemistry