Long-term changes of infra-littoral zone zooxanthellate cnidarians in the Taisho Lava Field, Sakurajima, Kagoshima, Japan

Abstract

In order to investigate long-term changes in a zooxanthellate cnidarian community in the temperate- subtropical area, we marked off a 41 m 2 area at Taisho Lava Field, Sakurajima, Kagoshima, Japan. Colonies of three zooxanthellate cnidarian species (encrusting anem- one Zoanthus sansibaricus Carlgren, soft coral Stereo­ nephthya japonica Utinomi, and bubble anemone Entacmaea quadricolor sensu Fautin and Allen) in the survey area were monitored yearly in August from 1995 to 2004. Sea- water temperature data were also obtained to investigate possible environmental influences on observed cnidarian changes. Sequences of internal transcribed spacer region of ribosomomal DNA (ITS-rDNA) were also obtained to identify the dinoflagellate Symbiodinium spp. endosym- bionts found within each cnidarian species (subclade C1/ C3 in Z. sansibaricus and E. quadricolor, clade G in S. japonica). Our results show that abnormally high ocean temperatures in 1998 (>2.0℃ than average summer sea water temperatures) were followed by significant decreases in both cover and colony number in S. japonica, which showed no sign of recovery to the previous level. The difference in changes between the three zooxanthellate cnidarian populations may be pri marily due to physio- logical differences at high ocean tem peratures in Symbio­ dinium spp. hosted by the three cnidarian spp..