Floodplain wetlands of the Gellibrand estuary: What type of invertebrate community

Introduction. Along the south coast of Australia, wetlands on the floodplains of lowland rivers and estuaries have been severely altered by agriculture and urbanization. Efforts to restore or rehabilitate these wetlands are hampered by insufficient knowledge of the original condition of these wetlands, or their variability in time and space. This research describes the macroinvertebrate community of wetlands on the floodplain of the Gellibrand River and estuary, which has suffered comparatively few human impacts. The aim of the research was to describe the variability of macroinvertebrate communities as a baseline for the future management of these wetlands, and to contribute to the general understanding of estuary-floodplain wetlands, thereby improving the basis for their management.

The Gellibrand River has a catchment area of approximately 1200 km2 draining the western slopes of the Otway Ranges, and entering the Southern Ocean at Princetown. From a mean annual flow of 315 000 mL, 25 000 mL are removed per annum for agricultural and domestic use (O'May & Wallace 2001), and flows are closer to natural regimes than most other Western Victorian rivers. The estuary is a bar-built, salt-wedge estuary that becomes completely blocked by the sand bar in most years, during summer and autumn. Over past decades, the estuary mouth has been opened artificially in most years. to prevent flooding of agricultural land and roads adjacent to the wetlands. At its maximum, the salt-wedge penetrates approximately 10 km upstream from the river mouth, but the estuary may also be completely fresh during high winter discharge
(Mckay 2000).

The wetlands surrounding Princetown cover 119 ha and are listed as nationally important (Environment Australia 2001). This listing regards the wetlands as an important habitat for animals at vulnerable stages of their life cycle and a refuge from adverse conditions, such as drought. They are a good example of coastal brackish and freshwater marshes, with an important ecological and hydrological role as part of a large wetland
complex.