Not a Fun Threesome: the Prevalence, Impact and Interaction of Boring Sponges and Pea Crabs on Oysters

The eastern oyster, Crassostrea virginica, provides a number of ecosystem services and is an important commercial fishery species along US East and Gulf Coasts. Unfortunately, their populations have declined dramatically, due to overharvest, habitat loss, and disease. As both oyster restoration efforts and aquaculture of oysters continues to increase throughout their range, it is important to consider the impacts of a number of potential oyster pests, including the boring sponge Cliona spp. and the pea crab Zaops (Pinnotheres) ostreum on oyster populations. Both of these pests have been demonstrated to reduce oyster growth, condition, and in some instances, reproductive output. Boring sponges in particular are a major concern for both oyster growers and managers, and our monitoring efforts have suggested that pea crabs might be more prevalent in sponge-infested oysters. We conducted an observational study to determine if there was any relationship between pea crab prevalence and sponge presence, and to examine whether the presence of both pests had synergistic effects on oyster condition. Across two very different systems (NC and NJ), sponge infested oysters were more likely to have a pea crab than the background population, both reduced oyster condition in isolation, and the effects were additive.