Coral reef degradation: a long-term study of human and natural impacts

Long-term annual monitoring of coral reef communities on the north coast of Jamaica has revealed dramatic changes over the past two decades caused by natural and human stresses. Coral cover at replicate sites and depths has declined from 27-77% in the 1970's to less than 5% at most locations in 1990. Conversely. macroalgal cover has increased sharply from 1-3% cover before 1983 to >90% today. The species composition of coral. algal and herbivore assemblages has also changed markedly. Several major reef zones described earlier in pioneering studies by T.F. Goreau and colleagues, no longer exist (e.g. those formerly dominated by Zoanthus spp., Acropora palmata and A. cervicornis). Damage from two hurricanes (in 1980 and 1988) has been exacerbated by overfishing. which along with mass-mortalities of sea urchins (1983) has resulted in a sustained algal bloom that continues to prevent normal recovery of corals. Monitoring techniques alone were not always sufficient to uncover the mechanisms causing shifts in species composition. A parallel program of experiments, demographic analysis and life history studies has clarified why some species have declined while others have increased, and suggests some management options. The prospects for recovery of coral abundances in the short- and medium-term are poor. These results have numerous implications for the design of global reef-monitoring programs