INFAUNAL COMMUNITY CHANGES AS A RESULT OF COMMERCIAL CLAM CULTIVATIONAND HARVESTING

Manila clams, Tapes philippinarum (Adams and Reeve) are cultivated ben eath plastic netting, to protect them from excessive predation? and ha rvested after approximately two years. Both the on-growing and harvest ing process have the potential to alter benthic communities. In order to study these effects, we surveyed a clam lay and uncultivated areas at a site of commercial clam cultivation in south-east England. Survey s were undertaken at the end of the growing stage, immediately after h arvesting by suction dredge and seven months later. Infaunal abundance was greatest within a net covered clam lay than in proximate and dist ant control areas, but the total number of species encountered was sim ilar in all areas (20-22). These differences were not attributable to variation in sediment structure or environmental variables between the areas sampled. Tube-building polychaetes, such as Lanice conchilega a nd Euclymene lumbricoides, were particularly abundant within the culti vated area as was the errant polychaete, Syllis gracilis. Harvesting b y suction dredge altered sediment composition by removing the larger s and fractions down to the underlying clay substratum, consequently the re was a large reduction in the density of all individuals and the tot al number of species. Seven months later, no significant difference wa s found between the infaunal community in the harvested clam lay or ei ther of the control areas and sedimentation had nearly restored the se diment structure. These observations indicate that the practice of cla m cultivation does not have long-term effects on the environment or be nthic community at this site.