Abstract

More than 120 species of marine water striders (Hemiptera, Gerromorpha), representing three families and eight genera, are distributed throughout the lndo-Pacific region. They live in marine habitats such as mangroves, intertidal coral reef flats and the sea surface near coral and rocky coasts. Five species of sea skaters, Halobates (Gerridae), have colonised the surface of the open ocean. Adult marine water striders are wingless but may disperse along coasts, chains of islands and possibly across wider stretches of open sea. Although some species of coral bugs, Halovelia (Veliidae) and Halobates are widespread, most species of marine water striders have rather restricted distributions. Cladistic hypotheses are now available for the genera Halovelia, Xenobates (Veliidae) and Halobates. Based upon distributional data for about 110 species, a number of areas of endemism can be delimited within the Indo-Pacific region. The results of component analyses of taxon-area cladograms for several monophyletic species-groups of marine water striders are presented.

The faunas of northern New Guinea, the Bismarck and Solomon Islands (Papuasia) are closely related and show much greater affinity with Maluku, Sulawesi and the Philippines than with the fauna of northern Australia. Relationships between the faunas of Papuasia + Sulawesi + the Philippines and those of Borneo + Jawa + Malaya are relatively weak. Marine water striders endemic to islands of the western Pacific show relationships among themselves and with Australia. Most marine water striders from the Indian Ocean (East Africa, Madagascar, Mauritius, Seychelles and Maldives) can be derived from the Indian-South-east Asian fauna. Composite faunas of marine water striders (either of different age or origin) are found in New Guinea, New Caledonia, Fiji Islands, the Philippines, tropical Australia and East Africa. The biogeography of marine water striders does not support the traditional division of the Indo- Pacific into the Ethiopian, Oriental and Australian regions. The distributional patterns are more compatible with a set of hierarchical relationships between more restricted areas of endemism.