The effect of marine reserves and habitat on populations of East African coral reef fishes

The effects of fishing, the duration of protection from fishing, features of the reef habitat, including benthic cover and sea urchin abundance, and the distance between reefs were examined to determine the ability of these factors to predict ecological aspects of fish communities. Population density, species richness, and rarity were estimated for 127 species of coral reef fish on 22 patch and fringing reefs along ∼400 km of East African coastline. The reefs included five protected areas, of which three study sites were protected for more than 25 years, and four sites were protected less than 10 years. Habitat variables were often significantly associated with fish community variables in fringing reefs, but not in patch reefs. Fish diversity was positively correlated with hard coral and coralline algal cover, and negatively correlated with sea urchin and algal turf abundance. However, multiple regression analysis suggests that protection from fishing was the single strongest factor affecting fish abundance and diversity. Consequently, many of the habitat correlations were probably due to direct and indirect effects of fishing on reef ecology, where heavy fishing results in increases in sea urchin and algal turf abundance and reduces hard coral and coralline algal abundance. Protected areas had higher abundances and species richness of commercially important triggerfish, surgeonfish, and parrotfish. There was, however, no relationship between local rarity in our study sites with rarity at the level of the western Indian Ocean for three well known fish families of angelfish, butterflyfish, and damselfish. Older reserves had more and rarer species than young reserves or fished reefs; and, consequently, the maintenance of reserves older than 10 years may be needed to sustain the full local diversity of fishes.