Recovery of corals a decade after a thermal stress event at Motobu, Okinawa, Japan: spatial variability in winners and losers

Abstract

Coral communities at nine sites off the coast of Motobu, Okinawa, were examined 6 and 12 years after a 1998 mass coral bleaching event caused by anomalous seawater temperatures. Overall, mean coral coverage in- creased from 17% in 2006 to 28% in 2010 at these sites, although these percentages were lower than the coral coverage at a nearby reef at Sesoko Island. Some of the corals that had not recovered (the “losers”) at the Sesoko reef were found at some sites in the present study. Domi- nant coral taxa differed among sites, probably because of differences in the environmental conditions at the sites, e.g., the so-called massive-type coral Porites dominated at a protected site near a river, while branching-type Acropora was dominant at exposed sites. Acropora was one of the prominent short-term losers, but contributed significantly to coral coverage increases due to its fast growth at some exposed sites. Adjacent reefs, which may share similar environmental conditions, also showed some variability, possibly due to processes such as coral recruit- ment and post settlement survival, which acted on a smaller spatial scale. Multivariate analyses such as multi- dimensional scaling were more sensitive than univariate analyses. Overall, recruitment was low, especially at sites with high coral coverage, which implies that remnant corals may have contributed to the recovery of these reefs. Coral communities in this area are recovering and there has been no apparent shift to algae-dominated commu- nities. The recovery of coral communities appears to be related to the life history traits of corals and environmental conditions.