Does stocking of grazing crabs ( <i>Maguimithrax spinosissimus</i> ) facilitate the survival and growth of out‐planted corals?

Abstract Introduction Macroalgal overgrowth on Caribbean coral reefs exacerbates coral disease and compromises the settlement, growth, and reproduction of corals. A new technique to combat the resultant coral‐to‐macroalgae phase shift is the stocking of native crabs ( Maguimithrax spinosissimus ) that graze on algae. Objectives This study investigated the efficacy of crab stock enhancement in facilitating the success of out‐planting corals on coral reefs in the Florida Keys, Florida, United States. Methods Coral fragments of three coral species (one branching coral: Acropora cervicornis ; two boulder corals: Montastrea cavernosa and Pseudodiploria clivosa ) were out‐planted on 32 patch reefs at two inshore and two offshore locations. Half of the reefs were stocked with crabs. Macroalgal cover on each patch reef along with the survival and growth of out‐planted corals was then monitored during the summer and winter for 2 years. Results There was no effect of crab stocking on macroalgal cover and crabs had little effect on the growth or survival of A. cervicornis . However, the presence of crabs improved the growth and survival of the two boulder coral species, although the magnitude of those effects varied by reef location. Conclusions Previous studies have heralded the strong effects that crab grazing has on reducing macroalgae and improving coral recruitment on reefs. The former was not observed in this study, although stocking crabs improved the success of coral out‐planting, with results varying by species and reef location.