Population dynamics of corallivores (Drupella and Acanthaster) on coral reefs of Koh Tao, a diving destination in the Gulf of Thailand

Diving-related tourism is known to contribute both directly and indirectly to reef degradation around the globe, including Koh Tao, a popular diving destination in the Gulf of Thailand. Of the known publications on reef threats at Koh Tao, only three mention the effects of highly abundant coral predators. The present study combines results of a nine-year long period (2006–2014) of reef surveys to evaluate the abundance and impact of corallivorous Drupella snails and Acanthaster sea stars in this area. It also provides the first record of their simultaneous outbreaks on Koh Tao’s reefs. The results are compared to those of other studies in order to evaluate how coral predation has influenced declines in reef health. The findings suggest that the combined effect of these corallivores has contributed substantially to coral degradation over the last decade and indicate that future assessments of reef decline in areas impacted by heavy tourism also need to address the effect of coral predation.