Epifaunal invertebrates as predators of juvenile bay scallops (Argopecten irradians)

Abstract

Predation strongly influences populations of numerous benthic invertebrates, although many predation studies to date have focused on macroscopic individuals, ignoring critical early life stages. Juveniles of the bay scallop, Argopecten irradians, settle and grow on the blades of eelgrass, Zostera marina, then migrate to the sediment surface when their mobility and size provide a refuge from benthic predators. During their time in the eelgrass canopy, scallops co-occur with a diverse array of small invertebrates, including peracarid and small decapod crustaceans, whose role as predators is largely unexplored. We measured consumption by amphipods, isopods, and a shrimp on recently settled bay scallops ranging in size from 0.5 to >1.5mm in a series of 24-hour experimental laboratory assays. These invertebrate predators, which were common concurrent epifaunal surveys of restored eelgrass beds in the mid-Atlantic, consumed up to 63% day−1 of juvenile scallops when the scallops were <1mm, but predation impacts decreased as scallops exceeded this size. Our data have implications for current restoration of both bay scallops and their eelgrass habitat, suggesting that previously unrecognized consumers may significantly affect scallop population dynamics at early life stages.