Proactive Ecological Reef Rehabilitation for Caribbean Coral Reefs

Coral reef formation is a function of deposition and erosion modulated by biological and physical forcing functions. In 1982-4, the Caribbean-wide mass mortality of Diadema antillarum, the long-spine sea urchin phase-shifted coral reefs into algal gardens. With few exceptions, Diadema’s ecological role has not been replaced and coral cover and recruitment have dropped precipitously. Additional local to global stressors have accelerated the decline and Caribbean reefs are losing their three-dimensionality and ecological integrity. Most are mere ghosts of their luxuriant past as bioerosion is overtaking accretion melting them into carbonate sand. In some shallow reef habitats Diadema populations have regenerated and their herbivory cleans the reef substrate of micro and macro algae. These reefs have high rates of recruitment and are showing signs of regeneration. The deeper reefs, without D. antillarum are mired in algae and show no potential for recovery without increased herbivory.

We transplanted shallow water D. antillarum to the deeper fore reef slopes of Jamaican and Belizean reefs in an attempt to understand why the species is restricted to the shallows. The urchins were initially caged at densities of 5–20/m² for three days to protect them while acclimating to their new habitat and to track their algal consumption. Upon cage removal, we found that the Diadema had efficiently removed the complex algal community from the substratum and the edges of live corals. Over the next week, the urchins remained together and continued foraging out from their previously caged area.

Algal overgrowth is widespread throughout the Caribbean and Western Atlantic and is generally agreed upon to be one of the major drivers of Caribbean coral reef collapse. While D. antillarum may eventually extend its range deeper, the current rates of degradation highlight the need for proactive reef restoration efforts to prevent collapse of the deeper reefs.