Western Port: a marine biodiversity assessment

Western Port and Port Philip Bay are large estuarine basins formed within a tectonic depression. Both estuaries were flooded at a similar time, at the end of the last glacial period as sea level submerged Bass Strait. Western... [ view full abstract ]

Western Port and Port Philip Bay are large estuarine basins formed within a tectonic depression. Both estuaries were flooded at a similar time, at the end of the last glacial period as sea level submerged Bass Strait. Western Port however supports higher species diversity and contains faunal elements not present in nearby Port Phillip Bay – a surprising result given both bays have been estuarine for the same period of time and contain a similar range of habitats.

The current marine invertebrate diversity of Western Port remains poorly known; the best data derived from a 1975 study was incompletely analysed. The question arises as to whether the biological differences are a result of incomplete data or whether the temporal stability of the habitats within each basin has driven speciation. Our project addresses these questions, using archived museum collections, recent field invertebrate sampling and sediment coring. Preliminary radiocarbon dating results indicate that the Western Port sediment flats are not recent feature but have been intertidal for the duration of the Holocene highstand and are 7,000 years old. Our study has also highlighted disparities in sampling effort and taxonomic identification between surveys over the last 40 years, which has restricted conclusions relating to changing patterns in Western Port invertebrate diversity. However, using some well-studied polychaete groups it seems possible that species diversity in Western Port is not unusually high but rather supports a unique composition of species. Future directions for our research will include other coastal embayments along the southeast Australian coast to understand the relative influence of geological history versus more recent, anthropogenic stressors on patterns of marine biodiversity.