Mass Mortality of Diadema antillarum on the Caribbean coast of Panama

Lessios, H; Cubit, J; Robertson, D; Shulman, M; Parker, M; Garrity, S; Levings, S

The ecologically important sea urchin Diaderna antillarum suffered mass mortalities in 1983, first noted in Panama and then reported from the rest of the Caribbean. We documented the effects of this mortality in two localities on the Atlantic coast of Panama, Punta Galeta and the San Blas Archipelago. At Punta Galeta, affected by the mortality in January 1983, the numbers of D. antillarum changed from an estimated 40,000 per 2.9 ha in June 1982 to 6 per 12 ha in May 1983; by February 1984 they had increased to 458 per 12 ha. In the San Blas, where mass mortality started in April 1983, the number of D. antillarum in permanent quadrats on 8 reefs was reduced by an average of 94.2 %. The average population density reduction measured in transects on nine reefs was 98.9 %. Data taken in permanent quadrats on four reefs in 1978, 1979 and 1980 indicate that population fluctuations of D. antillarum are normally much smaller, justifying the labeling of the 1983 event as ''mass mortality". Size structure of the San Blas populations was also affected; mean test diameter of D. antillarum on four reefs was reduced from 48.6 mm to 25 mm. The echinoids Echinometra viridis, E. lucunter, Lytechinus variegatus, L. williamsi, Eucidaris tribuloides, Tripneustes ventricosus, Clypeaster rosaceus and Echinoneus cyclostomus suffered no ill effects at either Galeta or the San Blas; their population densities remained stable or increased. Population density determinations of Diadema mexicanum at the island of Taboguilla on the Pacific side of Panama indicate that Diaderna mass mortality did not extend to the eastern Pacific. Sea surface temperatures, tidal levels, rainfall and salinity showed no abnormal fluctuations during the time of D. antillarum mass mortality at Galeta, suggesting that mortality was not due to physical stress. The wide geographical spread and the species-specificity of the mortality suggest a water-borne pathogen as the most likely causative agent. Recovery of D. antillarum populations is likely to be slow because there are few, if any, unaffected populations in the Caribbean to contribute larvae for the recolonization of depleted areas. The absence of D. antillarum will probably be reflected by changes in the algal, coral and echinoid communities, and by altered patterns of bioerosion.