Does Size Matter: Are Mesopredators Controlling Oyster Populations in Southeast North Carolina Estuaries?

Eastern oyster, Crassostrea virginica, restoration efforts seek to enhance populations by combating recruitment limitation.   Although typically considered to be limited by larval supply or substrate availability, post-settlement mortality can also lead to oyster recruitment failure.  Our previous research suggests that only the exclusion of predators by caging was effective at increasing oyster recruitment.  Decapod crustaceans are among the most important oyster predators, and it has been suggested that mesopredators, such as xanthid crabs, could be the dominant predators of juvenile oysters.  However, most studies have employed lab consumption rates and field densities to draw these conclusions.  In our study, we deployed a series of different sized mesh cages at a field site in southeast North Carolina to exclude groups of predators in order to test whether mesopredators are responsible for the majority of juvenile oyster predation.  The results suggest that mesopredators are either the dominant predator or at least capable of matching the consumption of larger predators.  In addition, we tested whether location within a site – reefs fringing marshes or reefs on mud flats – also had an effect on predation.  While predation was higher along the salt marsh, predation at both locations was attributable to mesopredators.