Impact on the coral reefs at Yongle Atoll, Xisha Islands, South China Sea from a strong typhoon direct sweep: Wutip, September 2013

Abstract

Relatively little is known about the extent and distribution of damage to coral reefs by typhoons in the South China Sea, especially in remote reefs where typhoons occur frequently. A strong Typhoon, Wutip (JTWC Category 3), directly struck the Yongle Atoll on 29 September 2013, causing 62 deaths and sinking dozens of ships in the Yongle Atoll maritime area, Xisha Islands, South China Sea. Surveys on coral reefs at Yongle Atoll were conducted using scuba diving before (July 2013) and after (8days) the typhoon sweep. The results show that the effects of Wutip on coral reefs were patchy as a result of varying coral reef geomorphology and depth. The typhoon caused significant damage to reef associated depths on the passage of the atoll, where currents generated by the typhoon produced the strongest energy. Coral destruction was most spectacular at the 2m depth (46% living scleractinian corals were damaged). At 6m and 15m depths, damage to the coral reefs were minimal. The shallow fore-reef area on the steep slopes, the upper region of the outer slopes with depths between 2 and 6m, were the principal zones of the typhoon effect. However, the vertical part of the steep slopes were mainly damaged indirectly waves rolling boulders or corals, which were less severely affected than the shallow fore-reef steep slope area. On the low angle slopes, the correlation between the typhoon damage to coral reefs and depth was low because the wave and current energy induced by the typhoon were homogenously attenuated along gentle slopes. Under the stress of global warming, destructive damage to coral reefs on the Xisha Islands is expected to increase, and will require frequent monitoring to determine trends in the near future.