Impact on the Coral Reefs at Yongle Atoll, Xisha Islands, South China

Journal of Asian Earth Sciences 114 (2015) 457–466 Contents lists available at ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes Impact on the coral reefs at Yongle Atoll, Xisha Islands, South China Sea from a strong typhoon direct sweep: Wutip, September 2013 ⇑ Hongqiang Yang b, Kefu Yu a,b, , Meixia Zhao b, Qi Shi b, Shichen Tao b, Hongqiang Yan b, Tianran Chen b, Guohui Liu b a Coral Reef Research Centre of China, Guangxi University, Nanning 530004, PR China b Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, PR China article info abstract Article history: Relatively little is known about the extent and distribution of damage to coral reefs by typhoons in the Received 3 October 2014 South China Sea, especially in remote reefs where typhoons occur frequently. A strong Typhoon, Wutip Received in revised form 25 March 2015 (JTWC Category 3), directly struck the Yongle Atoll on 29 September 2013, causing 62 deaths and sinking Accepted 1 April 2015 dozens of ships in the Yongle Atoll maritime area, Xisha Islands, South China Sea. Surveys on coral reefs at Available online 18 April 2015 Yongle Atoll were conducted using scuba diving before (July 2013) and after (8 days) the typhoon sweep. The results show that the effects of Wutip on coral reefs were patchy as a result of varying coral reef geo- Keywords: morphology and depth. The typhoon caused significant damage to reef associated depths on the passage Typhoon Wutip of the atoll, where currents generated by the typhoon produced the strongest energy. Coral destruction Coral reefs Yongle Atoll was most spectacular at the 2 m depth (46% living scleractinian corals were damaged). At 6 m and 15 m Xisha Islands 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 6 m, 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. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction coral reef communities directly, by generating physical devastation or indirectly as a result of stresses, such as enhanced turbidity, dis- Coral reefs are suffering from a variety of natural and anthro- ease outbreak, changes in predator behaviour or fresh water pogenic disturbances, including coral bleaching, ocean acidifica- inflow. On coral reefs, tropical storms cause small to large reduc- tion, coral diseases, tropic storms, over-fishing, pollution and tions in the abundance, area of coverage and species richness of tourism; these disturbances have resulted in significant degenera- corals. tion of complex coral reef ecosystems (Carpenter et al., 2008; The magnitude of damage to coral reefs by tropical cyclonic Comeau et al., 2014; Graham et al., 2013; Hoegh-Guldberg et al., storms at regional and local scales has been well studied (Done, 2007; Hughes et al., 2003; Johns et al., 2014; Nystrom et al., 1992; Gardner et al., 2005; Woodley et al., 1981). The scale and 2000; Osborne et al., 2014; Roff and Mumby, 2012; Yang et al., spatial degree of tropical storm effects on coral reefs vary widely, 2014; Yu, 2012; Zhao et al., 2012). Among them, ocean acidifica- from cases of negligible disturbance to the great devastation of a tion, coral bleaching and increased tropical storm intensity, which three-dimensional reef structure. A large amount of studies have are associated with climatic change, are currently acknowledged as also documented typhoon damage from direct mechanical disrup- having a severe negative impact on coral reefs. Severe tropical tion, sedimentation, salinity changes and turbidity (Cheal et al., storms, which are interrelated with climatic change, influence 2002; Harmelin-Vivien, 1994; Harmelin-Vivien and Laboute, 1986; VanWoesik et al., 1995). Direct physical disturbances not only include the effects of waves induced by tropical storms, such ⇑ Corresponding author at: Coral Reef Research Centre of China, Guangxi University, Nanning 530004, PR China. as dislodgement, overturning, coral breakage and the horizontal E-mail address: [email protected] (K. Yu). movement of debris (Bries et al., 2004; Fabricius et al., 2008; http://dx.doi.org/10.1016/j.jseaes.2015.04.009 1367-9120/Ó 2015 Elsevier Ltd. All rights reserved. 458 H. Yang et al. / Journal of Asian Earth Sciences 114 (2015) 457–466 Scoffin, 1993; Woodley et al., 1981), but also the damage caused by et al., 2012). These simulations indicate that the mean magnitude rolling coral rubble or boulders from steep slopes (Fabricius et al., of tropical storms will increase markedly in the immediate future. 2008; Harmelin-Vivien and Laboute, 1986). During tropical storm Scoffin (1993) indicated that the South China Sea reef areas are events, a considerable quantity of sediment is transported and frequently exposed to tropical storm disturbances, but more recent deposited. Some debris rolls into deeper sub-reef environments work shows that past tropical storms occurred frequently for the along steep slopes or is propelled onto beaches above sea level last several thousand years. Using high-precision ageing of across reef-flats (Done, 1992; Harmelin-Vivien and Laboute, storm-transported large Porites blocks on the Yongshu Reef, Yu 1986). The surface salinity changes rapidly, induced by river flood- et al. (2004, 2009) recognized six strong storm events with an aver- ing and torrential rainfall related to tropical storms, which may age period of 160 years during the last millennium. Yu et al. (2009) result in the death of coral colonies living in the shallow sea also found that storm activities in the South China Sea increased (Harmelin-Vivien, 1994; Williams and Bunkley-Williams, 1990). over the last 4000 years by analysing both lagoon sediments and Intense water movements induced by tropical storms stir sediment wave-transported coral blocks. However, in contrast to abundant material in lagoons and reefs. In addition, heavy rainfall results in scientific achievements on the possible effects of modern tropical turbid waters flowing into the reef area. These lead to an increase storms on coral reefs from the Great Barrier Reef and the in water turbidity that may decrease the available light for coral Caribbean Sea, there is still little known about how typhoons influ- colonies (Riddle, 1988). ence coral reefs in the South China Sea. When Typhoon Wutip One of the predictable results of global climate change is an struck the Yongle Atoll, we were conducting field investigations enhancement in the tropical storm intensity and possibly the fre- on the atoll, which provided an excellent opportunity to directly quency over the next 100 years (Knutson and Tuleya, 2004; observe the effects of the typhoon on the coral reefs. Trenberth, 2005; Walsh and Ryan, 2000; Webster et al., 2005). Recent analysis indicates that following global climate change, 2. Study site the proportion of Category 4–5 hurricanes (super typhoons) will rise at a rate of approximately 40% in proportion per °C increase The Yongle Atoll, a remote near-continuous annular coral atoll, in the Anthropogenic Climate Change Index (ACCI) (Holland and is located in the Xisha Islands, South China Sea, 300 km southeast Bruyere, 2014). Numerical modelling of the influence of global of Hainan Island and 80 km southwest of Yongxing Island (Fig. 1). changes may predict the incidence of tropical storms intensity, dis- Twelve islands and reefs developed on the reef rim that encom- tribution, and frequency (Davis and Bosart, 2002; Gopalakrishnan passes a lagoon of approximately 200 km2. Around the atoll rims Fig. 1. Maps of the Xisha Islands, Yongle Atoll, showing their location in the South China Sea and the sampling sites. (a) Site of the Xisha Islands, South China Sea. Track of Wutip through the South China Sea from 27 to 30 September, 2013 (Purple line). (b) The location of the Yongle Atoll, the Xisha Islands. Typhoon Wutip stuck directly on 29 September, 2013 (Purple line). (c) Site of the Yongle Atoll (16°21042.4900 N, 111°26058.2200 E 16°38020.2300 N, 111°48050.2200 E, Google Earth 2014). 1. Lingyang Reef, 2. Ganquan Island, 3. Shanhu Island, 4. Quanfu Island, 5. Yinyu Reef, 6. Jinqing Island, 7. Chenhang Island, 8. Jinyin Island. Typhoon Wutip stuck directly on 29 September, 2013 (White dashed). Survey sites after typhoon Wutip from October 6–12, 2013. Station 1: Western side of Lingyang Reef; Station 2: Northern side of Lingyang Reef; Station 3: Southern side of Shanhu Island; Station 4: Northern side of Shanhu Island; Station 5: Northern side of Quanfu Island; Station 6: Eastern side of Yinyu Reef; Station 7: Western side of Yinyu Reef. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) H. Yang et al. / Journal of Asian Earth Sciences 114 (2015) 457–466 459 there are several deep and wide passages that allow for an other benthic component covers, including dead scleractinian exchange between lagoon water and the open ocean (Fig. 1c). coral, algae, soft coral, reef-rock, rubble and sand were quantified, The climate in the Yongle Atoll region is dominated by the measuring the living scleractinian coral and other benthic compo- northeast monsoon from November to February, with a mean daily nents in centimetre length underlying the line transect.

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