Recovery of the sea urchin Diadema antillarum promotes scleractinian coral growth and survivorship on shallow Jamaican reefs

The decline and potential recovery of Caribbean reefs has been the subject of intense discussion and is of great interest to reef ecologists and managers. The recent return of Diadema antillarum sea urchins at some Caribbean locations and the concomitant changes in coral cover and recruitment provide a new perspective on the reversibility of Caribbean coral reef decline. This study examined the influence of recovering populations of Diadema and the subsequent formation of dense urchin zones on the growth and density of newly settled juvenile scleractinian corals. In these urchin zones, where Diadema graze algae, we documented higher growth rates of juvenile corals, and higher densities of small juvenile recruits (likely to be important precursors to reef recovery). Coral survivorship was higher for juvenile corals living in urchin versus algal zones. Roughly 83% of the juvenile corals in urchin zones survived over the 2 yr period of the study, while ~69% survived in the algal zones. Corals in the urchin zones increased in major diameter by an average of 75 7% from 2001 to 2003 versus 24 4% for corals in the algal zones during the same time period. The relatively abrupt decrease in macroalgal cover and the signs of increasing coral cover along the north coast of Jamaica following the return of Diadema, reported here and by other authors, suggest that these reefs have undergone rapid phase shifts, rather than being constrained to alternate stable states. In the Caribbean, it appears that Diadema are effective at enhancing scleractinian coral recruitment and growth and thus could be used as an important manipulative tool for returning reefs to a coral dominated state, especially on reefs that are severely overfished.