Stability and change in a changing environment: soft-bottom benthic molluscs in the Peel-Harvey Estuary over 42 years

Context. Eutrophication caused extensive macroalgal blooms in the Peel-Harvey Estuary, Western Australia, in the 1970s. Nutrient inputs were reduced and an artificial channel was constructed in 1994 to increase marine flushing. Aims. This study examines benthic mollusc populations in the estuary in 1978, 2000 and 2020, to determine what changes have occurred in the estuaries over time. Methods. Quantitative samples were made at 10 sites in autumn and spring of each year; physical and chemical parameters were measured in 2000 and 2020. Key results. Species composition was stable, dominated by Arthritica semen and Hydrococcus brazier!; however, there have been substantial changes in abundance of these and less common species. Conclusions. The exact cause (s) of density changes could not be determined, but it is likely to be due to a combination of factors. Implications. Further changes in mollusc assemblages in south-western Australian estuaries are expected as the climate warms and dries and the estuaries are stressed by human population growth.