Roberts, C.M.

Scuba diving on coral reefs is an increasingly lucrative element of tourism in the tropics, but divers can damage the reefs on which tourism depends. By studying the effects of diving we can determine what level of use is justifiable in balancing objectives of economic gain and conservation. Off the Caribbean island of Bonaire we compared coral and fish communities between undived reserves and environmentally similar dive sites where maximum use reached 6000 dives per site per year. At these levels of diving, direct physical damage to reefs was relatively minor. There were more loose fragments of living coral in dive sites than reserves and more abraded coral in high- than low-use areas. Diving had no significant effect on reef fish communities. Between 1991 and 1994, diving intensity increased 70% and coral cover declined in two of three dive sites and in all three reserves, suggesting a background stress unrelated to tourism. There was a significant decline in the proportion of old colonies of massive coral species within dive sites (19.2% loss), compared to a smaller loss in reserves (6.7%). Branching corals increased by 8.2% in dive sites, compared with 2.2% in reserves. Despite close management of reefs, diving is changing the character of Bonaire's reefs by allowing branching corals to increase at the expense of large, massive colonies. The impact of background stresses on massive corals seems to have been greater in the presence of diving. Other studies have linked disease infection to coral tissue damage, and the higher rates of abrasion we recorded in dived sites could have rendered corals there more susceptible to disease, thus mediating the decline of massive corals. Our study shows that even relatively low levels of diving can have pronounced effects manifested in shifts in dominance patterns rather than loss of overall coral cover. Bonaire's reefs have among the highest coral cover and greatest representation of ancient coral colonies of reefs anywhere in the Caribbean. Conserving the character of these reefs may require tighter controls on diving intensity.

Coral reefs worldwide are attracting increasing numbers of scuba divers, leading to growing concern about damage. There is now a need to manage diver behaviour closely, especially as many dive companies offer unlimited, unsupervised day and night diving from shore. We observed 353 divers in St. Lucia and noted all their contacts with the reef during entire dives to quantify rates of damage and seek ways of reducing it. Divers using a camera caused significantly more contacts with the reef than did those without cameras (mean 0.4 versus 0.1 contacts min-1), as did shore versus boat dives (mean 0.5 versus 0.2 contacts min-1) and night versus day dives (mean 1.0 versus 0.4 contacts min-1). We tested the effect of a one-sentence inclusion in a regular dive briefing given by local staff that asked divers to avoid touching the reef. We also examined the effect of dive leader intervention on rates of diver contact with the reef. Briefing alone had no effect on diver contact rates, or on the probability of a diver breaking living substrate. However, dive leader intervention when a diver was seen to touch the reef reduced mean contact rates from 0.3 to 0.1 contacts min-1 for both shore and boat dives, and from 0.2 to 0.1 contacts min-1 for boat dives. Given that briefings alone are insufficient to reduce diver damage, we suggest that divers need close supervision, and that dive leaders must manage diver behaviour in situ.