Abstract
Temperate wetlands and estuaries are widely regarded as the most degraded of all aquatic ecosystems, largely due to their exposure to a range of deleterious anthropogenic influences. In the case of the Vasse-Wonnerup Wetland System (VWWS) near Busselton, such impacts have included, land clearing for agriculture and associated severe eutrophication, the diversion of river flow and the construction of barriers (floodgates) to prevent the intrusion of saltwater into the wetland. Although the prevention of flooding and maintenance of surrounding pastoral land has been achieved, the VWWS has also suffered from numerous fish kill events and algal blooms. Current managers are thus faced with the problem of managing the legacy of historical management decisions, while also being under community and political pressure to introduce additional (but non-compromising) measures to reduce the frequency and severity of fish kills and algal blooms. This presentation details the anthropogenic changes that have occurred in the VWWS over the last 200 years and describe the resultant changes in environmental conditions, particularly salinity. The implications of these changes are then explored by comparing the fish and macroinvertebrate communities within different parts of the wetland in different seasons and also to those fauna recorded in other local systems. These analyses show that while the invertebrate fauna comprises wetland/freshwater species, the fish fauna of the VWWS is typical for an estuary. The compositions of both faunas undergo marked seasonal and regional changes in response to changes in salinity. The preliminary results of an acoustic tracking study demonstrate that, by understanding the movements of selected fish throughout the VWWS, management strategies could be refined to mitigate the effects of poor water quality and prevent or reduce the severity of fish kills.