| Disease outbreaks cause widespread mortality to corals. Patterns of disease incidence suggest environmental factors may have an impact on the microbial communities of corals and the occurrence of disease. Studies were undertaken to determine how bacterial communities inhabiting corals change in response to environmental factors. Analyses of terminal restriction fragment length polymorphisms (TRFLP) of 16S rRNA gene sequences show significant differences in bacterial communities of polluted and control localities only at the shallowest seawater depth, and that bacterial communities are different in heated versus control aquaria. Furthermore, differences in bacterial communities were found with increasing water depth. Comparisons of TRFLP peaks with sequenced clone libraries indicate the black band disease (BBD) cyanobacterium clone CD1C11 is common and most abundant on healthy corals in less than 10 m water depth. Similarly, sequences belonging to a putative new division of phototrophic bacteria, herein named CAB-I, were also more common in shallow water.; To assess the influence of environmental and physiologic factors on bacterial community structure, canonical correspondence analysis was performed using explanatory variables associated with: (1) light availability; (2) seawater pollution; (3) coral mucus composition; (4) the community structure of symbiotic algae; and (5) the photosynthetic activity of symbiotic algae. 11% of the variation in bacterial communities was accounted for by covariation with these variables; the most important being sunlight and the coral uptake of sewage as recorded by the delta15N of coral tissue.; It was also determined that in addition to the BBD cyanobacterium, five species of Firmicutes, two species of CFB group, and one species of delta-proteobacteria, are also abundant in the infectious BBD mat. Of these, six were consistently detected on healthy corals, four of which were found to be present at much higher numbers in BBD mats compared to healthy corals.; The extent of phenotypic plasticity in the corallite morphology of colonies of M. annularis s.s. was determined by analyzing the three-dimensional morphology of calical surfaces and the two-dimensional corallite morphology as represented in transverse thin sections. Significant phenotypic plasticity was found between seawater depths and localities, as well as between two geographic regions, Curacao and Panama. |
