FORAGING AND IMPACTS BY BENTHIC FISH ON THE INTERTIDAL AMPHIPOD COROPHIUM VOLUTATOR

We studied feeding site selection and impacts by benthic fish (flounder and skates) on the amphipod Corophium volutator, an ecologically-important species in muddy intertidal communities. We determined that benthic fish foraged mainly in areas that had high densities of amphipods, on a mudflat in Nova Scotia, Canada. This observation was based on recording sediments displaced by benthic fish in areas where samples of amphipods also were taken. From gut-content analysis, we found that benthic fish fed almost entirely on C. volutator, and most consumed smaller amphipods than expected based on samples of amphipods collected from the substrate. Benthic fish also fed on male amphipods more than expected. We determined that daily foraging pressure by benthic fish on amphipods was low (about 0.3% per day) by measuring the new appearance of feeding traces made by fish. Nonetheless, fish are expected to have substantial impacts on demography of C. volutator due to the length of the fish foraging season and because fish appear to contribute to extreme female-biased sex ratios typically seen in this species.