Impacts of diving tourists on coral reef community structure and herbivorous reef fish foraging behavior

Abstract

Increasing contact between humans and nature can disturb essential processes within ecosystems. Chronic anthropogenic disturbances on coral reefs may shift benthic community composition leading to loss of reef growth and biodiversity. The use of coral reefs for ecotourism can promote economic growth and conservation, if well managed. The presence of ecotourists has the potential to damage the benthic community through direct contact with corals and to disrupt foraging behavior by herbivorous fishes. I report here how reef community structure varies along a gradient of ecotourism use, and how tourist presence affects herbivorous reef fish behavior in the short- and long-term, on an intensively-visited portion of the Mesoamerican Barrier Reef. In Akumal Bay, Mexico, tourist use varied from low on reefs in the southwestern end of the bay, to very high (~ 1079 snorkelers per day) in the northeastern area of the bay. Reef-building coral cover decreased and macroalgal cover increased significantly with the level of tourism. Sea urchins exhibited species-specific trends related to tourism level. Neither the abundance nor diurnal foraging patterns of herbivorous fishes varied significantly with tourist abundance in the bay, suggesting a lack of long-term changes in fish behavior. However, they exhibited significant short-term responses to the experimentally-manipulated presence of divers. I recommend that reef managers should enforce carrying capacities for tourist use per day on coral reefs, to limit the types of ecosystem disturbances described here.