Predation of newly settled juvenile Crassostrea virginica often dominates post-settlement mortality. Resident mesopredators such as the xanthid mud crabs are abundant (>200/m2) on constructed subtidal oyster reefs in the New York metropolitan region and may contribute to post-settlement oyster mortality. Two study sites with differing mesopredator species, Hastings and Soundview Park, were selected to examine the role of small crustacean predators in post-settlement mortality. The white-fingered mud crab (Rhithropanopeus harrisii) inhabits Hastings, whereas the flat mud crab (Eurypanopeus depressus) and Sayi mud crab (Dyspanopeus sayi) inhabit Soundview Park. Using size-selective mesh cages to exclude predators, the effects of predator size on oyster predation and recruitment at Hastings and Soundview Park were examined. Overall, Soundview Park had higher consumption rates than Hastings. The highest consumption at Soundview Park occurred when predators of all sizes had access to the oyster prey. Larger-sized predators were likely responsible for oyster mortality, as oyster mortality was not different between the mesopredator and no-predator treatment at Soundview Park. Few oysters recruited at Soundview Park; thus predator size effects on oyster recruitment could not be effectively evaluated between sites. Recruitment at Hastings was not affected by predator-exclusion treatments, in agreement with the oyster predation experiments. Though abundant, no mud crab mesopredator recovered at either site was greater than 22mmin carapace width. Mesopredators were likely not of sufficient size to be dominant predators of newly settled juvenile oysters at Hastings and Soundview Park. Instead, predation pressure at Soundview Park was likely due to larger mobile predators such as blue (Callinectes sapidus) and spider crabs (Libinia spp.). Mesopredator size is an important factor to consider when evaluating mesopredator roles on oyster reefs.
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Vol. 35 • No. 4