Ecological status of coral reefs in the Spratly Islands, South China Sea (East sea) and its relation to thermal anomalies

Abstract

The Spratly Islands are a large group of more than 150 different coral formations from reefs to islands scattered between 6° and 12° N and 111° and 117° E in the southern part of the South China Sea. In addition to overfishing, dredging, and land reclamation in the area, an increased frequency of thermal anomalies resulting from global climate change has had an increasing effect on the coral reefs of the Spratly Islands. The coral surveys conducted in 2018–2019 on 15 sites within the archipelago revealed certain transformations of coral communities as a response to repetitive temperature stress. These transformations are expressed in shifts toward the dominance of thermally-resistant coral taxa with a stress-tolerant life strategy and in changes in size–frequency distribution of thermally-susceptible taxa toward the dominance of younger generations. Thermally-resistant taxa were dominant in 11 of 15 sites; eight of 15 sites were dominated by stress-tolerant taxa. The mean coral cover was 36.6%; the highest contribution in the total cover belonged to Acropora (27%), Porites (17.4%), and Pocillopora (4.1%). The high number of coral formations within the Spratly archipelago, high reef connectivity, and coral diversity determine the persistence of high reef resilience potential in the area.