Transitions in coral communities over 17 years in the Sekisei Lagoon and adjacent reef areas in Okinawa, Japan

Abstract

AbstractLong‐term monitoring reveals coral community responses to multiple disturbances that allow us to track their trajectories. We assessed the status of coral communities between 2000 and 2017 in the Sekisei Lagoon and adjacent areas in Okinawa, Japan, using an analysis of monitoring data collected from 196 research sites. Using categorical clustering, we ranked the coral cover in the sites according to five groups: (a) high, (b) intermediate, (c) low, (d) rapidly increasing and (e) unrecovered coral cover. We also identified the composition of assemblage types that were categorized according to the dominant species, and calculated the mean number of Acropora spp. juveniles for each group. Severe declines in the coral cover ranking were observed in response to bleaching events in 2007 and 2016. Although the coral cover rank of the other groups slowly returned to previous levels after the 2007 event, group 5, which accounted for 31% of all sites, did not. Group 5 sites were mainly located in the middle and southern area of the Sekisei Lagoon and along the Ishigaki Island, and were dominated by the Acropora spp., that are more susceptible to disturbances. The intermediate number of Acropora juveniles may also have hindered the recovery of corals in group 5 sites. Our study demonstrated that the coral community composition, in particular the proportion of Acropora spp. and juvenile recruitment, influenced the trajectory of coral cover and, therefore, should be considered when predicting the response of coral communities to climate change scenarios.