Latitudinal changes in hermatypic coral communities from west Kyushu to Oki Islands in Japan

Abstract

Hermatypic coral communities were quantitatively described along a latitudinal gradient from Koshiki-jima Islands (Kagoshima Prefecture) to Oki Islands (Shimane Prefecture) in western part of the mainland Japan in 2002-2009. In this region, most coral communities with relatively high coverage and species diversity occurred on hard substrates shallower than 10m at small and turbid baymouths protected from severe wave actions. Their habitats gradually shifted into two different environments with increasing latitudes; (1) shallower and sheltered areas inside small bay, and (2) deeper slopes ranging in depth from 15 to 20m near an offshore but semi-sheltered environment. Subtropical Acropora species A. hyacinthus with a tabular form and A. muricata with a branching form, and Pavona decussata with vertical plates were dominant at Kamikoshiki-jima in Koshiki-jima Islands. Coral communities near an offshore environment at Fukue-jima and Wakamatsu-jima in Goto Islands (Nagasaki Prefecture) were characterized by temperate and tabular Acropora (A. glauca, A. solitaryensis and A. japonica), whereas those in a semi-sheltered environment were dominated by temperate and branching Acropora tumida and A. pruinosa and/or encrusting to massive species such as Leptastrea pruinosa, Mycedium elephantotus and Hydnophora exesa. There occurred no tabular Acropora species at Iki and Tsushima Islands (Nagasaki Prefecture), where massive Favia spp., foliaceous to encrusting Echinophyllia spp. and Lithophyllon undulatum were dominant. Only three species (Massive to encrusting Oulastrea crispata, Alveopora japonica and Psammocora profundacella), which formed sparse populations were found at Oki Islands. The latitudinal changes in coral communities from west Kyushu to Oki Islands can be correlated well with the decrease in sea surface temperature (SST) that is also related to the warm Tsushima current, a branch of Kuroshio Current. Thus, it is important to monitor these coral communities in order to clarify changes in a coastal (shallow-water) ecosystem in this region because the increase in SST is expected in the near future as the global warming progresses.