The Siganidae, comprising 26 marine tropical Indo-West Pacific fishes, range from East Africa to French Polynesia. The larvae are pelagic but juveniles and adults live in the littoral/sublittoral zones. One species is estuarine; 13 are obligate corallophiles; and the remainder may also
occur on coral reefs. Species richness is highest in the Indo-Malayan area, lowest in French Polynesia, while East Africa occupies an intermediate position. There are five pairs of sibling species of which one of each pair has an Indian Ocean centered distribution and the other a Pacific Ocean
centered distribution. The eastern and western limits of the ranges of these pairs are confluent in the Indo-Malayan area. Thus part of the overall species richness of this area, at least for siganids (and for some other taxa as well), is an artifact resulting from it being a zone of overlap
of two faunas—one distributed from Indonesia to the Gulf of Oman and the other from Indonesia to French Polynesia. The effect of Quaternary lowerings of sea level on the Indonesian region has probably been responsible for this differentiation into separate Indian and Pacific Ocean faunas.
Other distinct zoogeographical subdivisions of siganid distribution, as evidenced by the extent of endemism in particular areas after the scheme of Briggs, coincide with the W. Indian Ocean, Red Sea and N. W. Australia Provinces. However, there are no endemic siganids in the peripheral island
groups of the central Pacific. The only two siganids to have penetrated some of these remoter areas are very wide ranging species, distinguished by their spending extended periods in the open sea as part of their early development. Conversely, the extremely similar species of the subgenus
Lo, which lead a sedentary existence among reef corals and might be expected to have abbreviated larval life spans, are comparatively not wide ranging. Further, in this subgenus speciation appears to have occurred in peripheral, isolated populations rather than in the central Indo-Malayan
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