DISTRIBUTION AND BIOGEOGRAPHIC RELATIONSHIPS OF THE HYDROID FAUNA OF THE AUSTRALIAN WEST-COAST - A PRELIMINARY ACCOUNT

Distribution and biogeographic relationships of 148 hydroid species fr om the western coast of the Australian continent bordering the Indian Ocean are examined. Faunal distribution along the western coastline is controlled by two major oceanic currents, the tropical Leeuwin Curren t and the warm temperate Western Australian Summer Current. A zone of confluence between the temperate and tropical hydroid fauna occurs at latitude 26 degrees S with an attenuated zone of overlap existing to 3 4 degrees S. Ferry-four per cent of the western Australian fauna occur s in south and south-eastern Australia and 24% on the subtropical and tropical eastern coast. A distinct overlap zone of tropical and temper ate species occurs at Shark Bay. About half of the 25 species known fr om the southern Indian Ocean occur on the western Australian coast. Tw enty-six per cent of the western fauna is common to southern and easte rn Africa, 32% to the tropical Indian Ocean and Indonesian archipelago and 18% to the Indo-west Pacific.