Scuba diving damage and intensity of tourist activities increases coral disease prevalence

Recreational diving and snorkeling on coral reefs is one of the fastest growing tourism sectors globally. Damage associated with intensive recreational tourist use has been documented extensively on coral reefs, however other impacts on coral health are unknown. Here, we compare the prevalence of 4 coral diseases and 8 other indicators of compromised coral health at high and low use dive sites around the island of Koh Tao, Thailand. Surveys of 10,499 corals reveal that the mean prevalence of healthy corals at low use sites (79%) was twice that at high use sites (45%). We also found a 3-fold increase in coral disease prevalence at high use sites, as well as significant increases in sponge overgrowth, physical injury, tissue necrosis from sediment, and non-normally pigmented coral tissues. Injured corals were more susceptible to skeletal eroding band disease only at high use sites, suggesting that additional stressors associated with use intensity facilitate disease development. Sediment necrosis of coral tissues was strongly associated with the prevalence of white syndromes, a devastating group of diseases, across all sites. We did not find significant differences in mean levels of coral growth anomalies or black band disease between high and low use sites. Our results suggest that several indicators of coral health increase understanding of impacts associated with rapid tourism development. Identifying practical management strategies, such as spatial management of multiple reef-based activities, is necessary to balance growth of tourism and maintenance of coral reefs. (C) 2014 Elsevier Ltd. All rights reserved.