Zoological Studies

Vol. 37 No. 4, 1998

Zoogeography of Shore Fishes of the Indo-Pacific Region

John E. Randall

Bernice P. Bishop Museum, 1525 Bernice St., Honolulu, Hawaii 96817-2704, USA

John E. Randall (1998) The East Indian region (Indonesia, New Guinea, and the Philippines), with perhaps as many as 2800 species of shore fishes, has the richest marine fish fauna of the world. The numbers of species of fishes decline, in general, with distance to the east of the East Indies, ending with 566 species in Hawaii and 126 at Easter Island. The richness of the marine fauna of the East Indies is explained in terms of its relatively stable sea temperature during ice ages, its large size and high diversity of habitat, in having many families of shore fishes adapted to the nutrient-rich waters of continental and large island shelves that are lacking around oceanic islands, in having many species with larvae unable to survive in plankton-poor oceanic seas or having too short a life span in the pelagic realm for long transport in ocean currents, and in being the recipient of immigrating larvae of species that evolved peripherally. It is also a place where speciation may have occurred because of a barrier to east-west dispersal of marine fishes resulting from sea-level lowering during glacial periods (of which there have been at least 3 and perhaps as many as 6 during the last 700 000 years), combined with low salinity in the area from river discharge and cooling from upwelling. There could also have been speciation in embayments or small seas isolated in the East Indian region from sea-level lowering. Sixtyfive examples are given of possible geminate pairs of fishes from such a barrier, judging from their similarity in color and morphology. Undoubtedly many more remain to be elucidated, some so similar that they remain undetected today. Fifteen examples are listed of possible geminate species of the western Indian Ocean and western Pacific that are not known to overlap in the East Indies, and 8 examples of color variants in the 2 oceans that are not currently regarded as different enough to be treated as species. Five examples of species pairs are cited for the Andaman Sea and western Indonesia that may be the result of near-isolation of the Andaman Sea during the Neogene. Explanation is given for distributions of fishes occurring only to the east and west of the East Indies in terms of extinction there during sea-level lows. The causes of antitropical distributions are discussed. The level of endemism of fishes for islands in the Pacific has been diminishing as a result of endemics being found extralimitally, as well as the discovery of new records of Indo-Pacific fishes for the areas. Hawaii still has the highest, with 23.1% endemism, and Easter Island is a close second with 22.2%. The use of subspecies is encouraged for geographically isolated populations that exhibit consistent differences but at a level notably less than that of similar sympatric species of the genus. In order to ensure continuing stability in our classification of fishes, a plea is given not to rank characters obtained from molecular and biochemical analyses higher than the basic morphological characters that are fundamental to systematics.

Key words: Indo-Pacific, East Indies, Speciation, Endemism, Subspecies.

*Correspondence: Tel: (808) 2351652. Fax: (808) 8478252. E-mail: johne@bishop.bishop.hawaii.org