The Effect of Increasing Habitat Complexity on Bay Scallop Survival in the Presence of Different Decapod Crustacean Predators

Predation is among the most important biotic factors affecting benthic populations. Habitat complexity, such as seagrass shoot density, can significantly reduce rates of predation by changing predator and prey behaviors, increasing searching and handling times, and reducing encounter rates; this relationship is assumed to be nonlinear. For bay scallops, and other commercially important seagrass-associated prey, understanding the relationship between survival and habitat can have important implications. In this study, we looked at the shape of the habitat survival function (HSF) for bay scallops across four different decapod predator species ( Callinectes sapidus , Carcinus maenas , Dyspanopeus sayi , and Libinia sp.) using a series of mesocosm experiments at four different levels of habitat complexity (0, 200, 400, and 800 shoots m−2). As expected, scallop survival was higher in the complex seagrass habitat than when no seagrass was present. However, the shape of the HSF varied among predators: when green crabs were predators, the HSF was linear, whereas the HSF was hyperbolic in the presence of both mud and blue crabs. These data suggest that even small increases of seagrass shoot density from very low levels may rapidly increase prey survival, but that prey survival is unlikely to increase across broad changes in habitat complexity. Further, this experiment suggests that predator identity may be important in determining the relationship between prey survival and habitat complexity. For scallop restoration, efforts can be enhanced by selecting even relatively low levels of seagrass habitat, regardless of perceived “value” based on shoot density.