Distribution and abundance of soft-bottom molluscs in Port Phillip Bay, Victoria, Australia

Abstract

The distribution of soft-bottom molluscs of Port Phillip Bay, Vic., is examined in terms of abundance, the distribution of feeding types and patterns of diversity, and related to environmental variables such as depth and sediment type. Six feeding types were distinguished among the 105 species collected. Infaunal suspension feeders dominated in marginal sandy substrates while surface deposit feeders dominated in the silt and clay sediments of the Central region and Corio Bay. Epifaunal suspension feeders, grazers, scavengers and predators were less abundant and were seldom dominant. Numbers of individuals and species, and diversity, varied widely but were generally higher in marginal areas. Four areas of the Bay were recognized on the basis of similarities in distribution patterns, the distribution of species numbers, of diversity and of the dominant feeding type: the Nepean sand banks, the deep water Central and Corio regions, marginal areas, and the shallow seagrass sand flats. The main determinants of mollusc distributions were substrate and food supply, while purely hydrological effects were limited to nearshore areas. Regional differences in diversity were related to sample size by correlation and regression; low faunal density caused diversity in the Exchange region to be considerably underestimated.