Management of scleractinian coral assemblages in temperate non-reefal areas: insights from a long-term monitoring study in Kushimoto, Japan (33°N)

In this era of global climate change, understanding fundamental mechanisms of coral community maintenance and persistence in temperate non-reefal areas is a high marine conservation priority. To identify mechanisms of community maintenance and persistence via larval supply, we monitored coral settlement over 12 years and investigated the genetic population structure of two major acroporid species at Kushimoto, Wakayama Prefecture, Japan (33°N). Between 8 and 30 artificial settlement panel pairs were deployed from May or June to September, October, or November of each year. Recruits on settlement panel pairs were scarce, especially those of acroporids (0 or < 1 recruit per panel pair in most years). As coral cover in the Kushimoto area remained relatively high over a decade, such low recruitment may be sufficient for persistence of acroporid communities in this region. In addition, genetic analysis using 8 or 10 microsatellite markers demonstrated differences in genetic structure between populations of Acropora hyacinthus, which is a long-term resident species in this area, and A. muricata, a recently arrived species. Acropora hyacinthus displayed higher numbers of multilocus genotypes (41 of 43 samples collected) whereas only one multilocus genotype in 30 samples was seen in A. muricata. This difference may reflect both the length of time since population establishment and morphology. Consequently, acroporid communities in the Kushimoto area are likely maintained by survival and growth of existing colonies and/or fragmentation, indicating that conservation of established corals should be the first priority to ensure persistence of coral assemblages in such temperate non-reefal areas