Coral responses to macroalgal reduction and fisheries closure on Caribbean patch reefs

To determine the effects of algal reduction and fisheries closure, a crossed experimental design was undertaken over a 516 d period on the remote patch reefs of Glover's Reef Atoll, Belize. We investigated (1) the effects on health, growth, and survivorship of 2 transplanted coral species, Porites asteroides and Siderastrea siderea, and (2) the changes in the benthic and fish communities. Algal reduction (98% reduction by physical removal kept low by monthly removal) increased the abundance of all fish and slightly elevated herbivore bite rates. P. asteroides showed a temporal response to environmental conditions opposite of predictions, with higher bleaching and mortality in the unfished reefs cleared of algae. This may be due to reduced water flow at these sites as the growth rate of P. asteroides was positively related to water flow (R-2 = 0.35, p = 0.04). S. siderea growth showed no relationship with water flow and bleached slightly more in the control reefs. Nevertheless, there were no patterns in mortality, and growth rates were twice as high in the fished than unfished reefs for this species. This reef-scale study contrasts with results of small-scale experiments that found rapid, indirect coral mortality from erect algae. Rather, our results suggest that environmental conditions, notably reef location in relation to water flow, can be a considerably stronger factor influencing coral health than erect algae.