BIOLOGY OF MODERN FRAGUM-ERUGATUM (MOLLUSCA-BIVALVIA, CARDIIDAE) IN RELATION TO DEPOSITION OF THE HAMELIN COQUINA, SHARK BAY, WESTERN-AUSTRALIA

Fragum erugatum populations were sampled over two consecutive years in Hamelin Pool, Lharidon Eight and Freycinet Harbour, which are represe ntative of the hypersaline and metahaline regimes of Shark Bay. F. eru gatum was widely distributed infratidally between 1.2 m and 6.5 m dept h. Dense aggregations of zooxanthellae were present in mantle and gill tissue. Shell shape of the population from Hamelin Pool differs from that of the Lharidon Eight, Freycinet Harbour and Dampier Archipelago populations. F. erugatum was found to be a synchronous hermaphrodite. Settlements of juveniles, and modality of size distributions, indicate a single annual spawning. Production estimates of dry flesh and shell (CaCO3 inclusive) were much lower in Hamelin Pool than in Lharidon Ei ght, largely because of the lower density of F.: erugatum recorded in Hamelin Pool. Although shells are washed ashore continuously, large-sc ale deposition of the accumulated infratidal coquinas, largely compose d of F. erugatum shells, probably occurs periodically in major storm e vents, thereby forming the Hamelin Coquina.