Diving associated coral breakage in Hong Kong: Differential susceptibility to damage

- Broken coral colony number is correlated with number of divers visiting.
- Branching and plate-like corals are susceptible to diver damages.
- Composition change of coral substrate has been taking place in Hong Kong.
- Popular dive sites should be zoned as “no-go” areas for training divers.

We conducted the first quantitative assessment of coral breakage along a gradient of diving activities in Hong Kong, the most densely populated city in southern China. A survey of six 1 × 25 m transects at seven sites revealed a total of 81 broken corals, among which 44% were branching, 44% plate-like and 12% massive. There were 3-19 broken colonies per site. At most study sites, the percentage of broken corals exceeded the recommended no-action threshold of 4%, suggesting that management intervention is justified. There was a significant positive correlation between the number of broken coral colonies and the number of divers visiting the site. The branching Acropora and the plate-like Montipora suffered from much higher frequency of damage than their relative abundance, raising the concern that the cumulative impact of such differential susceptibility to breakage may affect coral community composition.