The temperate seas of WA's south coast are subject to the variability of the Leeuwin Current. This band of warm, relatively-low-salinity, nutrient-depleted water starts near the North West Shelf, and travels down the west coast, wrapping around Cape Leeuwin and continuing eastwards as far as the Great Australian Bight, though it varies in strength from year to year. In so doing, it transports some tropical species of plants and animals to the temperate south coast of WA.

Along the western section of the coastline, which receives significant winter rainfall, there are numerous estuaries fed by winter-flowing rivers. Most of these are closed by sandbars and only open following heavy winter rains. The numbers of rivers and estuaries decreases to the east as the coastline becomes more arid. The limited run-off from rainfall combines with the effect of the Leeuwin Current to limit the nutrients available and hence the productivity of these waters. As a result there is high species diversity but low overall abundance for many marine animals.

It is a high energy environment heavily influenced by the swells generated in the Southern Ocean. There are few large areas of sheltered waters along the southern coast, the exceptions being around Albany and in the Recherche Archipelago off Esperance.

A unique assemblage of plants and animals has evolved in the waters of the south coast including large and spectacular fish such as the blue groper and the threatened great white shark. The south coast marine environment includes spectacular granite reefs, sponge gardens, limestone reefs, seagrass meadows, kelp gardens and communities of filter feeders in deeper waters. In the Recherche Archipelago off Esperance, the only area that has been intensively surveyed, scientists have also discovered large areas containing rhodolith beds of calcareous algae.

Leafy Seadragon (c) Ann Storrie

An extremely high proportion of species in Australia's southern waters are found nowhere else in the world, such as the remarkable and uncommonly seen leafy seadragon. When marine biologists surveyed the Recherche Archipelago they collected 300 to 400 species of sponges and around 40 to 50 per cent were new to science! Even in a better known group such as the fish, six new species were discovered.

New Zealand Fur Seals

Islands off the coast are home to colonies of New Zealand furseals, Australian sea lions, penguins and other seabirds, all of which depend on the sea to survive.