Diadema antillarum 17 years after mass mortality: is recovery beginning on St. Croix?

Abstract

Diadema antillarum was once ubiquitous in the Caribbean, but mass mortality in 1983-84 reduced its numbers by >97%. We measured Diadema abundance on back reefs and patch reefs that have been well studied for >25 years. From June 2000 to June 2001, popula- tions on back reefs have increased >100% (June 2001 mean densities 0.004-0.368/m 2 ), while patch reef popu- lations increased >350% (June 2001 densities 0.236- 0.516/m 2 ). Populations are dominated by small urchins, suggesting high recent recruitment. Increased Diadema densities appear to be affecting macroalgae abundance. The general spatio-temporal pattern of recovery around St. Croix seems to be following that of the die-off, sug- gesting that the same oceanographic features that spread Diadema's pathogen are now carrying urchin larvae.