Cellular responses of the long-spined sea urchin (Diadema antillarum-a)(160.9)

Abstract

Abstract The long-spined sea urchin (Diadema antillarum-a) began dying on coral reefs near the Panama Canal in 1983, and over the next year they virtually disappeared from the Caribbean Sea. Present evidence suggests that a water-borne pathogen was responsible. Since their die-off Diadema densities remain low, and as they facilitate coral recruitment and persistence by controlling macroalgae, its loss has contributed to the transformation of living coral reefs in the Caribbean to barren algae-covered rock. Our preliminary on-site studies of the humoral responses of the urchins showed that Diadema coelomocytes did not respond to lipopolysaccharide as vigorously as did other common Caribbean sea urchins (Tripneustes ventricosa, Echinometra lucunter, and E. viridis). We then studied the cellular immune responses of coelomocytes and coelomic fluid of Diadema and those of the other urchins unaffected by die-off. Light microscopy revealed differences in coelomocyte populations of the predominant urchins of the Caribbean. We used flow cytometry to investigate differences in cellular composition and responses of coelomocytes in phagocytosis assays. It is hoped that this research will increase insight into one of the most devastating and ecologically important die-offs ever recorded, as well as provide the information required to understand whether weakened immunity was involved in the mass mortality of Diadema antillarum-a, and whether strengthening of immunity has occurred since then.