The Importance of Mesopredators on Juvenile Oyster Predation: A Field Test

The eastern oyster, Crassostrea virginica, is a target species for many restoration efforts along the East and Gulf coasts of the United States. These restoration efforts typically seek to enhance populations by combating recruitment limitation. While recruitment of oysters is considered to be limited by low larval supply, or substrate availability, post-settlement mortality, particularly attributed to predation, can also lead to recruitment failure of benthic invertebrates such as oysters. Our previous research suggests that only the exclusion of predators by caging was effective at increasing oyster recruitment, regardless of seeding or settlement cues. Many species are implicated in predatory mortality of post-settlement invertebrates, although decapod crustaceans are among the most important. It has been suggested that the dominant predators of small oysters could be mesopredators such as mud crabs, despite their lower per capita consumption rates than larger predators, due primarily to their high abundances on oyster reefs. 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. In addition, we tested whether location within a site – reefs fringing marshes or reefs on mud flats – also had an effect on the importance of mesopredators on juvenile oysters.