After the long summer: Death and survival of coral communities in the shallow waters of Kume Island, from the Ryukyu Archipelago

Abstract

Coral reefs in the Ryukyu Islands, southern Japan, have been undergoing degradation for at least five decades. Recently, the archipelago has been hit by bleaching events for two consecutive years (summers of 2016–2017). Shallow coral communities have been reported as especially affected. In this study, using underwater transects, we assessed the status of shallow coral reef communities in Kume Island, at seven distinct locations in Shimajiri Bay, following reports from local fishermen and divers of heavy bleaching across the bay. Our data and analyses revealed that the benthic environment in the bay has algae as the main component, with an average coral cover of only 7.2%. Branching coral colonies, which used to be the most common morphology in Kume Island reefs, accounted for just 7.6% of the total coral cover. Notably, the genus Acropora was almost completely absent from our transects, although its recent presence was confirmed by dead colonies making up 4.12% of total transect coverage, suggesting that restoration efforts focused on this genus might be possible in the future. In order for these to be successful, however, a better understanding of the environmental situation at Kume Island is required, including the effects of human activities on coral reef communities.