More scuba diving means sicker coral reefs

The gorgeous coral reefs around Koh Tao, Thailand draw thousands of tourists every year. But frequent scuba diving appears to be increasing the rate of coral disease, threatening to spoil the natural resource that locals depend on for their livelihood.

Compared to fishing, tourism may seem like a relatively sustainable way to boost the local economy. On the island of Koh Tao, small fisheries have declined in favor of playing host to more than 300,000 divers per year. The number of visitors rose by roughly five times from 1992 to 2003, and about 50 dive operators now work on the island.

Previous studies have shown that diving can injure corals and stir up sediment. To study other aspects of coral health, researchers surveyed more than 10,000 corals at 10 reef sites around Koh Tao. Half of the sites were frequently visited by divers, and the other half were not. The team looked for signs of sickness such as white syndromes and brown band disease, as well as other health indicators such as bleaching and broken tips.

About 79 percent of the corals at the unpopular sites were healthy, while only 45 percent of those at popular sites appeared free of disease or damage, the researchers reported in Biological Conservation. Diseased corals were three times more common at the frequently-visited sites, and the team also saw higher rates of injuries, sponge overgrowth, abnormal pigmentation, and tissue necrosis caused by sediment.

Fortunately, a few simple measures could be taken to treat the reefs more gently. For example, setting speed limits for boats could reduce the amount of sediment that gets kicked up. Adding better sewage treatment systems to boats could cut wastewater pollution. And while it would be impractical to forbid tourists from visiting reefs, managers could better protect the corals by limiting the number of dive operators allowed at each site. Roberta Kwok | 21 August 2014

Source: Lamb, J.B. et al. 2014. Scuba diving damage and intensity of tourist activities increases coral disease prevalence. Biological Conservation doi: 10.1016/j.biocon.2014.06.027.

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