Biogeography community structure and diversity of Red Sea and western Indian Ocean butterflyfishes

Patterns of variation in the assemblage structure of butterflyfishes (Chaetodontidae) of the Red Sea and western Indian Ocean have been compared. There is a lower number of species in the Red Sea, a high proportion of which are endemic to the region, both features that have been attributed to the relatively recent origin of the Red Sea. In the Red Sea overall mean abundance of butterflyfish is greatest in the central part, decreasing both to north and south. Several species present in the southern Red Sea are absent from the north. By contrast, most western Indian Ocean species are widely distributed within the Indo-West Pacific. Comparative field studies in the northern Red Sea (Egypt) and western Indian Ocean (Kenya) showed that mean number of species was higher in the western Indian Ocean, but mean density of butterflyfishes was higher in the Red Sea. In both areas diversity of butterflyfish was related to mean substrate diversity (the number of coral growth forms). Mean spatial niche breadth of butterflyfish species was much higher in the Red Sea than in the western Indian Ocean, whereas the extent of microhabitat use was higher in the western Indian Ocean. It is suggested that these differences may be related to the more recent evolution of the Red Sea fauna.