Effects of recreational scuba diving on Caribbean coral and fish communities

Scuba diving on coral reefs is an increasingly lucrative element of tourism in the tropics, brit divers can damage the reefs on which tourism depends. By studying the effects of diving we can determine what level of use. is j ustifiable in balancing objectives of economic gain and conservation. Off t he Caribbean island of Bonaire we compared coral and fish communities betwe en undived reserves and environmentally similar dive sites where maximum us e reached 6000 dives pel site per year. At these levels of diving, direct p hysical damage to reefs was relatively minor: There were more loose fragmen ts of living coral in dive sites than reserves and more abraded coral in hi gh- than low-use areas. Diving had no significant effect on reef fish commu nities. Between 1991 and 1994, diving intensity increased 70% and coral cov er 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 site s (19.2% loss), compared to n smaller loss in reserves (6.7%). Branching co rals increased by 8.2% in dive sires, compared with 2.2% in reserves. Despi te close management of reefs, diving is changing the character of Bonaire's reefs by allowing branching corals to increase nt the expense of large, ma ssive colonies. The impact of background stress on massive corals seems to have been greater in the presence of diving. Other studies have linked dise ase infection to coral tissue damage, and the higher rates of abrasion we r ecorded in dived sites could have rendered comb there more susceptible to d isease, 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. B onaire's reefs have among the highest coral cover and greatest representati on of ancient coral colonies of reefs anywhere in the Caribbean. Conserving the character of these reefs may require tighter controls on diving intens ity.