Predator-prey interactions in a restored eelgrass ecosystem: strategies for maximizing success of reintroduced bay scallops (Argopecten irradians)

Predation is a key determinant of community structure and function, and thus should play a central role in successful ecological restoration strategies. The bay scallop, Argopecten irradians, was once abundant in the coastal bays of Virginia, U.S.A., until the complete loss of their eelgrass habitat, Zostera marina, in the 1930s. With the successful restoration of Z. marina in these coastal bays, attention has turned to reintroducing A. irradians with the intent of producing a self-sustaining population. The success of this effort requires an understanding of the sources and degree of natural mortality that A. irradians experiences throughout their ontogeny. The objectives of this study were to: (1) quantify predatory mortality during two successive life history stages of A. irradians, in both spring and fall spawns and (2) identify possible predators of A. irradians in the Virginia coastal bays. We conducted tethering experiments to quantify the proportional losses due to predation, and used otter trawls and suction samples to characterize the predator community over two consecutive years. Losses due to predation ranged from 4 to 80% per day, with smaller juveniles (<15 mm shell height) experiencing greater mortality in 2013, and larger juveniles (>20 mm shell height) in 2014, which we infer is driven by the absence and presence of adult blue crabs in 2013 and 2014, respectively. We propose that managers should look toward relatively inexpensive predator surveys to best judge both when and at what size restored species should be introduced into the wild.