Increasing temperature anomalies reduce coral growth in the Weizhou Island, northern South China Sea

The ways in which high-latitude corals respond to ongoing climate warming and the increasing incidence of extreme warm- and cold-water events remains unclear, probably due to a lack of field studies, especially in the northern South China Sea (NSCS). In this study, temporal variation in the skeletal growth rate in massive Porites lutea corals collected from the Weizhou Island, NSCS, was examined over a 27-year period (from 1984 to 2010). The coral skeletal extension rates were determined by using X-ray photography, and compared to the Degree Heating Weeks (DHWs) index (0–16.7 °C-weeks) and the Sea Surface Temperature (SST) Anomalies (0–0.6 °C for + SST_anomaly, and −3.2–0 °C for -SST_anomaly). Historical extreme high and low temperature events were calculated to estimate warm- (DHW > 6 °C-weeks, +SST_anomaly > 0.2 °C) and cold- (-SST_anomaly < −1.6 °C) water stresses on reef-building corals. The average skeletal growth rate for all coral colonies was 6.3 mm year−1, ranging from 3.1 to 9.9 mm year−1. Coral skeletal growth consistently showed a downward trajectory, especially after the year of 1997. The mean value was 7.3 mm year−1 from 1984 to 1996 and then declined by approximately 26% to 5.4 mm year−1 from 1997 to 2010. We found that an increasing frequency and intensity in warm- and cold-stresses can explain the observed decline in growth rate of Porites colonies in the Weizhou Island.