Environmental Effects of Shellfish Culture Structures along the Mid-Atlantic Region of the East Coast
Mark Luckenbach, College of William and Mary (panel moderator
Abstract
Over the past quarter century a substantial industry in bottom cultivation of hard clams, Mercenaria mercenaria, has developed along the U.S. mid-Atlantic coast. Off-bottom culture of the Eastern oyster, Crassostrea virginica, is also expanding within the region. These industries rely on a variety of structures, including nets, bags, cages and floats to provide predator exclusion and to suspend oysters in the water column. Considerable public attention has focused on the aesthetic impacts of these structures and problems associated with derelict gear, and the industry has responded by reducing impacts on the viewshed and improving gear removal. Little is known, however, about the broader ecological effects of these structures. Potential effects include impacts to predator populations through exclusion from foraging grounds, enhancement of non-bivalve prey species through the provision of refugia, the development of structure-associated communities and alterations of food webs. One short-term study found only limited overlap between migratory shorebird foraging grounds and clam aquaculture in Virginia, but further studies are needed. No studies have yet been conducted in this region examining the effects of shellfish aquaculture on other predator (e.g., fish, crustaceans and ducks) populations. On the other hand, enhanced abundances of macroinvertebrates and some juvenile finfish have been documented in association with oyster and clam aquaculture structures. For oyster aquaculture, enhanced faunal abundances are associated both with the structures and with oyster biomass. A persistent feature of M. mercenaria culture is the development of seasonally abundant macroalgae on the predator exclusion nets. These macroalgae have been shown to support a diverse faunal community, including juvenile blue crabs, and to provide occasional foraging grounds for shorebirds. Trophic models that integrate the exclusion of some predators, the enhancement of prey populations, and foraging by other predator species are needed to more completely evaluate the effects of shellfish culture structures