Habitat complexity and predator size mediate interactions between intraguild blue crab predators and mud crab prey in oyster reefs

The prevalence of inherently unstable intraguild (IG) predation in natural systems suggests that many biotic and abiotic factors, including habitat complexity and population size structure, affect interactions between IG predators and prey. We investigated the role of shared oyster resource use (Crassostrea virginica), predator size, and habitat complexity (i.e. sand, shell hash, and simulated oyster clusters) in mediating the interactions of IG predators, the blue crabs Callinectes sapidus, and IG prey, the mud crabs Panopeus herbstii, in oyster reef communities. In mesocosms, mud crabs consumed the shared oyster resource at higher rates than did blue crabs. Constructed oyster reef clusters in mesocosms reduced blue crab predation on mud crabs, suggesting increasing habitat complexity provides mud crabs with a more effective refuge from IG predators. Survival of mud crabs in less complex habitats depended on predator size; small blue crabs were not able to consume mud crabs in any habitat type. The refuge effects of oyster reefs were confirmed in the field using mud crabs tethered in sand, shell hash, and oyster clusters. These experiments demonstrate the importance of habitat complexity and body size in mediating intraguild interactions between blue crabs and mud crabs on oyster reefs; they also elucidate the impacts of these predators in oyster reef communities.