Effects of self-guided snorkeling trails on corals in a tropical marine park

Underwater trails are intended as interpretative tools in marine parks, but concentrating divers and snorkelers in defined areas may negatively affect the surrounding environment. We examined spatial and temporal patterns in the effects of use of underwater trails on coral reef flats in the Great Ba rrier Reef Marine Park, Australia. Changes in benthic assemblages were asse ssed on two new trails used by snorkelers, two unused (control) trails, and two undisturbed areas. Total percent coral cover, numbers of broken coloni es, and living coral fragments were counted 6 months before and 6 months af ter the new trails began to be used. Spatial patterns of effects around con centrated nodes of use were determined by stratified sampling around and aw ay from the interpretative signs within each trail. Despite comparatively l ow levels of use (approximately 15 snorkelers per trail per week), snorkele rs caused significant damage to corals along the trails. Branching corals ( non-Acropora branching corals and Millepora spp.) were most affected. More damage occurred near the interpretative signs than elsewhere on the trails. The numbers of broken branches and damaged coral colonies in the snorkelin g trails increased rapidly but stabilized within 2 months of the commenceme nt of use. There was no significant change in overall benthic assemblages w ithin the trails after 6 months of use by snorkelers. Although concentratin g snorkelers within confined trails caused increased damage to corals, the effects can be mitigated by appropriate design and placement of the traits and by managing the behavior of snorkelers. Interpretative information shou ld warn users about the damage they may cause when swimming along the trail s. Managing the behavior of snorkelers in the water is likely to be more ef fective in reducing damage than simply applying fixed limits to the amount of use the trails receive.