Modelling Oyster Population Response to Variation in Freshwater Input

Silt loadings associated with human activities in catchments were inferred to have an extremely widespread effect on estuarine macrobenthos around Tasmania. Estuaries with human population densities exceeding 10 km-2in catchments consistently possessed muddy rather than sandy beds and shores, and were dominated by infauna rather than epifauna. Estuaries with human population densities below 1 km-2in catchments possessed sandy sediments and numerous epifaunal species. These effects were consistent within groups of estuaries possessing similar hydrology and geomorphology. Although faunal composition differed substantially between estuaries possessing low and high human population densities, the number of macrofaunal species was similar. Population effects therefore could neither be detected using species richness indices, nor by the ABC method. Faunal changes were most clearly detected using disturbance indices weighted by the sensitivity of individual species to human activity. Two such indices, which are based on abundance (DIn) and productivity (DIp) data, are suggested to provide useful local indicators of estuarine health.