by JAMES M. CERVINO 1*, RAYMOND HAYES2, THOMAS J. GOREAU3, and GARRIET W. SMITH4
1University of South Carolina, Marine Sciences Department,Columbia, SC 29208, Email. cnidaria@earthlink.net; 2 College of Medicine, Howard University, Washington, DC; 3 Global Coral Reef Alliance, Cambridge, MA; 4 University of South Carolina, Aiken, SC USA;
Published in Symbiosis (37) 2004 pp. 63-85
To see images of yellowband disease documented by Craig Quirolo who first observed it at Key West-area coral reefs, go to:
Abstract
Impairment and breakdown in the symbiotic relationship between the coral host and its zooxanthellae has been documented in the major Caribbean reef building coral, pathogens and/or exposed to unusually high seawater temperatures. Progressive degradation of zooxanthellar cellular integrity occurs, leading to the deterioration of coral tissue. Cytoplasmic organelles were displaced and chloroplasts are reduced and marginalized which is accompanied by internal swelling, vacuolization, fragmentation, and loss of cell wall structural integrity. Changes in algae that occur in YBD-infected corals differ from changes seen in corals undergoing solely temperature-induced coral bleaching, however. In many disease-infected corals, there is no evidence of zooxanthella in the mucus, unlike in thermal bleaching, where zooxanthellae was evident in the coral surface layer. Isolated zooxanthellae inoculated with YBD pathogens showed a 96% decrease in chlorophyll a pigments compared to controls, and a 90% decrease in mitotic cell division over 96 hours of YBD bacterial inoculation (<p=0.0016). Cytoplasmic and organelle integrity is compromised after YB infection, while host tissue remains intact. The YBD bacterial pathogens seem to target the symbiotic zooxanthellae indicating an algal infection. Isolated zooxanthellae samples subjected to higher temperatures and bacterial pathogens reveal virus-like particles (VLP) that are observed within algal cytoplasm, but their significance remains unknown and requires further investigation. The results of this study suggest that YBD and other coral disease is primarily a disease of the symbiotic zooxanthellae rather than of the coral host. These data elucidate the different cellular mechanisms between thermal bleaching and coral diseases in the Caribbean and Pacific.
Received November 3, 2003; Accepted March 1, 2004