Department of Conservation and Land Management

Western Australia's Marine Biodiversity Setting

Western Australia's State Coastal Waters extend from latitudes 14° to 35° South and range from the warm, tropical waters off the Kimberley coast to the cool temperate waters of the Great Australian Bight. The coastline is over 13,000 kilometres in length and comprises about 40% of the continental coastline of Australia.

A unique feature of the coastal waters of Western Australia is the presence of a poleward, shelf-edge current of tropical water, the Leeuwin Current, which carries water derived in part from the Pacific-Indian Throughflow down the Western Australian coastline. The current flows year round but is stronger and closer to shore during autumn and winter due to the absence of the opposing southerly wind stress and associated nearshore northward counter-currents (eg the Capes and Ningaloo currents) that occur during the late spring and summer months. The Leeuwin Current has a major influence on the biogeography of the State’s marine flora and fauna and is responsible for the occurrence of tropical biota at latitudes further south than where these species are typically found elsewhare. Three major biogeographic zones occur: a tropical zone north of North West Cape, a temperate zone east of Cape Leeuwin and a biological overlap zone in between. Other major influences on the marine environment of Western Australia are the regular occurrence of severe tropical storms (i.e. cyclones), particularly off the northwest coastline, the low level of freshwater and sediment input to most of the nearshore waters of the State, the macro-tidal water level variations of the northwest coast and the high wave energy of the west and south coasts.

These natural characteristics and influences combine to produce a diversity of marine ecosystems and habitats unrivalled in other states of Australia. The conservation of Western Australia’s marine biodiversity is not only important from an intrinsic point of view, but also as the fundamental basis of major recreational, tourism, fishing and, potentially, pharmaceutical industries.