Recruitment of the subtropical coral Alveopora japonica in the temperate waters of Jeju Island, South Korea

Abstract

The zooxanthellate scleractinian coral, Alveopora japonica Eguchi, 1968, inhabits high-latitude waters from southern Taiwan to mainland Japan. This species may have benefited from recent increase in seawater temperature, and it has been hypothesized that a shift from kelp forest to coral dominance may be occurring at some locations at the edge of its distribution. Here, we examined the coral diversity and composition of the benthic community associated with extensive A. japonica stands from Biyangdo, northeast of Jeju Island (33.41 degrees N), South Korea. Coral recruit density was further examined by estimating the number of juvenile corals in photographs taken directly from the benthos. The depauperate coral assemblage (five species in total) was dominated by A. japonica, which contributed to 64.0% (SE 1.4%) of the benthic cover. Together with local reports documenting recent development of A. japonica populations, the exceptionally high density of recruits, 7590 (SE 660) recruits per m(2), suggests a population that could be increasing. Additional data are needed to correlate the trend observed in this population with rising seawater temperature. However, this "weedy" and opportunistic coral species may be colonizing the region more aggressively than expected by chance, possibly to the detriment of the original ecosystem dominated by macroalgae. Overall, this work constitutes an important baseline against which future changes recorded in the temperate benthic communities can be assessed.