BIOGEOGRAPHY OF THE TROPICAL SEAGRASSES IN THE WESTERN PACIFIC

Seagrass species and their distributions were recorded from 18 localit ies in the tropical and subtropical Pacific. These field observations were collated with a review of the recent literature, enabling the pre sent distribution patterns of seagrass species in the western Pacific to be described and the origin of those species to be discussed in rel ation to the major oceanic currents of the region. The major tropical seagrasses of the western Pacific are Thalassia hemprichii, Enhalus ac oroides, Cymodocea rotundata, C. serrulata, Halodule uninervis, Syring odium isoetifolium and Thalassodendron ciliatum, with T. hemprichii an d E. acoroides being the two most widely distributed species. Species are found in coastal waters along the Equatorial Countercurrent and th e Kuroshio and East Australian Currents. The highest number of seagras s species occurs in the coastal waters of Malesia enclosed by Indonesi a, Borneo, Papua New Guinea and the Torres Strait (northern Australia) . This area is considered to be the source of all of the seagrass spec ies of the western Pacific, i.e. the centre of their origin. A relatio nship between the distance from this centre of origin along the above three major ocean currents and the diversity of seagrass species was f ound: the further from the origin, the poorer the seagrass diversity. These observations support the centre-of-origin theory that was first proposed by den Hartog to describe the processes responsible for the p resent distribution patterns of seagrasses in the western Pacific.