Structure and dynamics of a high-latitude scleractinian coral community in Amakusa, southwestern Japan

This study examined structure and dynamics of a high-latitude scleractinian coral community in Amakusa, southwestern Japan (32 degrees N). All visible colonies (>similar to 5 mm in diameter) in an area of 100 m(2) were monitored for 2 yr (2001 to 2003). A total of 54 species belonging to 30 genera in 13 families were identified from 2471 colonies that covered 28.3% of the area in 2001. The majority of these were spawners with only 4 brooding species being identified or inferred. Faviidae was the most specious family (21 spp.), being dominant in terms of both colony number (49.8%) and cover (55.4%). In spawning genera, frequency distributions of colony sizes were characterized by a larger median size, wide size range and a tendency toward negative skewness, whereas in brooding genera, highest frequencies were in small size classes with a tendency toward positive skewness. Annual recruitment, dominated by Acropora and 3 brooding genera, was relatively constant (122 to 132 recruits) but always lower than annual mortality (death/dislodgement, 187 to 288 colonies), resulting in a rapid reduction in colony number (9%) in the 2 yr study period. Acropora and brooding genera accounted for 79% of the community turnover (mortality and recruitment) while many genera showed little or no change. Pocillopora showed the largest increase (+36 colonies) and Acropora the largest decrease (-127 colonies). During the study period, 57 colonies of middle to large size were lost (i.e. no skeleton remained) due to severe wave action caused by rough weather or typhoons, while colonies that died from other causes (418 colonies) were mostly of small sizes. Consequently, though deaths accounted for 88% of colony losses, lost colonies (i.e. those not counted as 'dead') accounted for 75% of coral cover reduction. This occasional loss of large colonies by severe wave action is likely to be a significant factor inhibiting the development of scleractinian communities and reef accretion, especially at high latitudes where these processes are considered to be slow.