Besides coral bleaching due to expulsion of its zooxanthellae, the grazing activities of the ‘Crown-of-torns’ or Acanthasther planci and the Drupella spp. shell also cause the corals to look bleached. The Crown-of-torns is related to the sea urchin, starfish and cushionstar, classified under the Phylum Echinodermata, whereas the Drupella spp. shell belongs to the phylum Mollusca. These corallivores that feed mainly on corals are known to cause devastation in a reef area if their populations explode unchecked. Numerous patches of bleached dead corals indicate their feeding voracious activities, whereby the corals died their calcium carbonate skeletons will be overgrown by algae. Newly grazed corals may also be easily mistaken as coral bleaching, but upon closer inspection, the difference between bleached and grazed corals can be discerned easily. Bleached corals are not necessarily dead, since despite losing their symbiotic algae they are still very much alive and most of the corals will regain their zooxanthellae once they are able to recover and cope with the stress. Bleached corals look extremely clean and somewhat glowing because they are able to actively remove sediment or other particulate matters that descend upon them. In contrast, grazed corals will be colonised by algae with the presence of a thin film or haze of green, brown or yellow.
In Malaysia, mass coral bleaching was first reported in 1998. The coral bleaching issue in Malaysia was still very new then, was little understood and drew scant attention. Subsequent reports on coral bleaching were those of Pulau Payar in 2001 and Pulau Langkawi in 2004, which were published in reefbase of Worldfish Centre. The most recent bleaching occurs in Tioman Island (2008), which has caught the eyes of many scientists and marine park managers in Malaysia. In this situation, the first course of action is to identify the sources of the stress, the extent of the coral area bleached and the best course of action to be taken. There are protocols and methods which have been developed to guide scientists and park managers in facing this epidemic, and most of these protocols are offered free online!"