INTERTIDAL CLAM HARVESTING - BENTHIC COMMUNITY CHANGE AND RECOVERY

Mechanical harvesting of intertidal bivalve molluscs inevitably leads to the physical disturbance of the substratum and its associated fauna . Hence, it is necessary to consider the consequences of such activiti es for the requirements of other species (e.g. fish and birds) which u tilize these areas. The present study reports a long-term experiment t hat studied the effects of Manila clam, Tapes philippinarum Adams & Re eve, cultivation on an estuarine benthic habitat and its fauna. The st udy began with the initial seeding of the clams, and continued through ongrowing, and finally, harvesting 30 months later. Earlier observati ons revealed that plots covered with netting elevated sedimentation ra te, and hence, encouraged the proliferation of certain deposit-feeding worm species which persisted throughout the cultivation cycle until h arvesting took place. The immediate effects of harvesting by suction d redging caused a reduction of infaunal species and their abundance by approximate to 80%. Recovery of the sediment structure and the inverte brate infaunal communities, judged by similarity to the control plots on both the harvested and unharvested but originally netted plots, had occurred 12 months after harvesting. Comparisons with other similar s tudies demonstrate that, in general, suction harvesting causes large s hort-term changes to the intertidal habitat. The rate at which recolon ization occurs and sediment structure is restored varies according to local hydrography, exposure to natural physical disturbance and sedime nt stability. The management of clam farming procedures and other form s of mechanical harvesting should incorporate a consideration of site selection, rotational seeding, cultivation and harvesting to create fa llow areas, and seasonal harvesting to ameliorate the recovery of site s.