ASPECTS OF VELIGER LARVAL GROWTH AND BYSSUS DRIFTING OF THE SPAT OF PECTEN-MAXIMUS AND AEQUIPECTEN-(CHLAMYS)-OPERCULARIS

Veliger larvae of Pecten maximus were reared from the early "D" larva stage to metamor-phosisat9,12,15, and 18°C. Growth rates andQ,0 values were calculated at the different temperatures. In conjunction with data from previous studies, the average length of planktonic life for P. maximus larvae was estimated to range from 78 days at 9°C to 24 days at 18°C.To investigate the potential for post-larval dispersal, the sinking rates of wild collected post-larvae (spat) of P. maximus and Aequipecten (Chlamys) opercularis, and laboratory reared spat of P. maximus, were measured in a glass tube. Spat of both species were sometimes able to slow their descent dramatically and it is proposed that, as with other bivalves, this was achieved by the production of a long, fine byssus drifting thread. The behaviour of some spat suggested that they could detach from the drifting thread and then secrete a further thread during their descent in the tube.The data are discussed in relation to the differing dispersal capabilities of these two scallop species, an important consideration for the management of their fisheries. © 1992 Oxford University Press.