Natural disturbances and interannual variability of coral reef communities on the outer slope of Tiahura (Moorea, French Polynesia): 1991 to 1997

We analysed the interannual variability of the major reef communities (algae, corals and fishes) on the outer slope of the Tiahura sector on Moorea Island between 1991 and 1997, and examined the impacts of natural disturbances on these communities. Patterns of temporal variation and the response to natural perturbations were clearly different among the taxa examined. A sharp decrease in the percent cover of branching corals (Pocillopora and Acropora) followed cyclonic and bleaching events that occurred in 1991. After 1993, a slight increase in coral cover values was recorded, and can be interpreted. as a sign of recovery. Despite a similar proportion of bleached colonies at the beginning of bleaching events in 1991 and 1994, the bleaching in 1994 had no significant impact on coral cover. This result demonstrates the importance of understanding the ecological history of reefs (i.e. the chronology of disturbances) in interpreting the specific impacts of a particular disturbance. The decline in coral cover was accompanied by an increase in the percent cover of turf algae, but surprisingly, the percent cover of macroalgae did not show any significant temporal variation during the 7 yr period. Thus, the decrease in the percent cover of corals, which opens up new substrate, does not always result in an increase in macroalgal cover. The temporal variation of the fish community was mainly characterized by (1) the high variability in the recruitment of juveniles, with a peak in 1991; (2) the slight increase in the density of adult species; and (3) the decrease in the density of corallivorous chaetodontid fishes from 1991 to 1994. Since corals were the only taxon directly affected by natural disturbances, they were consequently the cause of the indirect effects of these disturbances (i.e. increase in turf algae and decrease in chaetodontid fishes), and can therefore be regarded as the 'key component' of the outer slope reef communities in Moorea.