How small-scale variation in oyster reef patchiness influences predation on bivalves

ABSTRACT: As oyster fishing continues to degrade reef habitat along the US Atlantic coast, oyster reefs appear increasingly fragmented on small spatial scales. In outdoor mesocosms, experiments tested how consumption of representatives of 4 different bivalve guilds by each of 3 mesopredators varies between continuous and fine-scale patches of oyster reef habitat. The mesopredator that fed least (stone crab) exhibited no detectable change in consumption on any bivalve (ribbed mussel, bay scallop, hard clam, and 3 size classes of eastern oyster). Consumption of bay scallops by both blue crabs and sheepshead fish was greater in small patches than in continuous oyster reef habitat. Of the bivalve guilds tested, only the scallop possesses swimming motility sufficient to reduce predation, an escape response that would likely leave the bivalve protected within structured habitat in larger continuous oyster reefs. Sheepshead consumed more small oysters in the continuous habitat than in the fine patches, while no other predator–prey interaction exhibited differential feeding as a function of habitat patchiness. Consequently, predation by mesopredators on bivalves can vary with the scale of oyster reef patchiness, but this process may depend upon the bivalve guild. Understanding the role of habitat patchiness on fine scales may be increasingly important in view of the declines in apex predatory sharks leading to mesopredator release, and global climate change directly and indirectly enhancing stone crab abundances, thereby increasing potential predation on bivalves