A role for immune deficiency in the mass mortality of the Caribbean sea urchin Diadema antillarum-a?(160.10)

Abstract

Abstract Immune responses and diseases of marine invertebrates in natura are not well understood, and studies linking this knowledge to ecological events are rare. An epidemic nearly eliminated the long spined sea urchin Diadema antillarum-a from the Caribbean in 1983, with limited recovery since. Loss of this keystone grazer is a major factor in the ensuing shift from living coral to algae-covered rock on Caribbean reefs. Our studies of immune responses of four Caribbean sea urchin species suggest that a deficiency in the Diadema immune system may have played a role in the mass mortality. Using coelomocytes, we tested humoral responses of the urchins with classic stimulators in several assays. All urchin coelomocytes responded to stimulators with one statistically significant exception: Diadema did not respond as vigorously to lipopolysaccharide. This suggests a defect in immune response that is specific to Diadema and independent of stressors associated with particular environments. This inability of Diadema to respond to lipopolysaccharide provides the first evidence of a deficient immune response in a natural population of a marine invertebrate, and may help explain why Caribbean Diadema antillarum-a was vulnerable to an epidemic. Recovery of Diadema allows us to addresses questions on how recovery may be influenced by immunological processes. Further investigation of phylogenetic and geographic patterns in immunity of marine organisms may help us predict future epidemics.