First observed severe mass bleaching in Malaysia, Greater Coral Triangle

Abstract

Malaysia contains approximately 4,000 km2 of reef (Wilkinson 2008) and an estimated 500 hermatypic coral species, which constitutes more than 60% of the worlds described hermatypic coral species (Veron et al. 2009). However, these reefs are exposed to numerous anthropogenic pressures and more than 40% are classifi ed as having a high or very high Integrated Threat Index (Burke et al. 2002). Prior to 2010, severe and widespread coral bleaching had not been observed on Malaysian reefs, including during the 1997/98 global event when bleaching of Malaysian reefs was mild and occurred only in localized patches (Wilkinson 1998; Kushairi 1999). In 2010, bleaching began in mid-May along the north- western coast of Peninsular Malaysia; within three weeks, reefs around the major islands along the east coast were bleached (Fig. 1a). This event followed the peak of the third strongest El Niño event in the past 50 years (www.cgd.ucar.edu/cas/ENSO/enso.html). Around 50% of hard corals at Tioman (2°49′N, 104°10′E), Redang (5°46′N, 103°01′E) and Perhentian Islands (5°55′N, 102°44′) were bleached, with two-thirds of those col- onies completely white. During the underwater visual surveys (40 and 29 surveys around Tioman and Perhentian Islands, re spectively), bleached corals were observed down to 20 meters depth; at Redang Islands (54 surveys) bleaching was found as deep as 25 meters. The severity and extent of the bleaching was consistent with the observed level of satellite- derived thermal stress, exceeding 8 ℃-weeks (Liu et al. 2003; Fig. 2), In addition, outbreaks of an unidentifi ed disease increased the mortality rate of corals (Fig. 1b). In contrast, minimal bleaching was observed in EastMalaysia (Sabah and Sarawak) at this time (＜10%), again consistent with the thermal stress patterns (Sabah Parks and Reef Check Miri, unpublished data). These observations suggest that the scale of bleaching events in this region may be increasing, underlying the need to undertake effective management strategies to conserve and protect reefs from natural and anthropogenic threats.