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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 an...

We investigated the functional significance of intersexuality in the amphipod Corophium volutator, a key species in soft-bottom intertidal communities. Intersexes in this species possess morphological and anatomical characters of both males and females. Two broad types of intersexes were identified: those with nonsetose oostegites and two penial papillae (Type I), and those with setose oostegites and one or two penial papillae (Type II). We found little evidence that intersexes function as females, but some females housed experimentally with intersexes became ovigerous, indicating that intersexes can function as males. Females that mated with Type II intersexes produced smaller broods than those that mated with Type I intersexes or males, suggesting that this form of intersexuality may be costly to amphipods (most Type II intersexes possessed only a single testis). Male function of intersexes may be important in populations of C. volutator because males are frequently the limiting sex due to extr...