Responses of algae, corals and fish to the reduction of macroalgae in fished and unfished patch reefs of Glovers Reef Atoll, Belize

Macroalgae were experimentally reduced by approximately 2.5 kg/m(2) on eigh t similar-sized patch reefs of Glovers Reef Atoll. Belize, in September 199 8 Four of these reefs were in a protected "no-take" zone and four were in a "general use" fishing zone. Eight adjacent reefs (four in each management zone) were also studied as unmanipulated controls to determine the interact ive effect of algal reduction and fisheries management on algae, coral, fis h, and rates of herbivory, The 16 reefs were sampled five times for 1 year after the manipulation. We found that the no-fishing zone had greater popul ation densities for 13 of 30 species of fish, including four herbivorous sp ecies, but lower herbivory levels by sea urchins. However, there was lower stony coral cover and higher macroalgal cover in the "no-take" zone, both p rior to and after the experiment. There were no significant effects of mana gement on the percent cover of fleshy macroalgae. The algal reduction resul ted in an increase in six fish species, including four herbivores and two w hich feed on invertebrates. One species, Lutjanus griseus. declined in expe rimental reefs. Macroalgal biomass quickly recovered from the reduction in both management areas within a few months, and by species-level community m easures within 1 year, while stony coral was reduced in all treatments. Cor al bleaching and Hurricane Mitch disturbed the site at the beginning of the study period and may explain the loss of stony coral and rapid increase in erect algae. We suggest that reducing macroalgae. as a technique to restor e turf and encrusting coralline algae and stony corals, may work best after reefs have been fully protected from fishing for a period long enough to a llow herbivorous fish to recover (i.e. > 5 years). Further ecological studi es on Glovers Reef are required to understand the shift from coral to algal dominance that has occurred on this reef in the last 25 years.