Distribution of Temperate/Tropical Seagrass in Satsunan Islands and Adjacent Waters, Kagoshima Prefecture, Japan

Distribution of thirteen species of seagrass in Satsunan Islands and adjacent waters (Kagoshima Prefecture) was determined by herbarium specimens at Kagoshima University and Kagoshima Prefectural Fisheries Technology and Development Center. Furthermore, a field survey was carried out at two sites of seagrass meadows in Amami-Oshima Island to reveal the community structure of these meadows and their distributional ecotone of tropical and temperate species. Zostera， japonica and Halophila nipponica, collected from Amami-Oshima Is., were the only temperate species occurring in this region. Distributional limits of tropical species differed by the taxa. Six tropical species, Cymodocea rotundata , Cymodocea serrulata，Syringodium isoetifolium, Thalassia hemprichii, HaloPhila ovalis and HaloPhila decipiens, were confirmed from Amami-Oshima Is. and is appear to be at their most northern limit in the world. Meanwhile, two species of Halodule were confirmed at all major islands from south of Tanegashima Is., and Halophila major were confirmed from both Satsunan and southern part of Kyushu Islands. In general, T. hemprichii occurs as one of the more dominant species in reef-associated habitats in the Pacific tropical islands including the southern part of Satsunan Is. (i.e., Yoronjima, Okinoerabujima, Tokunoshima Islands). However, in Amami-Oshima Is., Halodule and Zostera were more common rather than the former