Investigating Acute Montipora White Syndrome in Kāne‘ohe Bay, O‘ahu: Causative Agents, Putative Environmental Drivers, and the Importance of Host Health.

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2017-05
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Beurmann, Silvia
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Microbiology
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Reports of disease-related coral mortality have increased over the last few decades. Coral diseases contribute to the decline of coral reefs globally and threaten the health and future of coral reef communities. There is an imminent need to develop our understanding of the biotic and abiotic drivers of coral disease outbreaks on an ecological and molecular level. Montipora white syndrome (MWS) is a tissue loss disease that affects populations of the coral Montipora capitata in Kāne‘ohe Bay, Hawai‘i. Two types of MWS have been documented; a chronic progressive tissue loss disease termed chronic MWS (cMWS), and a comparatively faster infection termed acute MWS (aMWS). Colonies exhibiting cMWS have been observed to spontaneously switch to aMWS in the field. This dissertation describes analysis of coral-associated bacterial communities, causative agents of disease, the importance of host health, and putative environmental drivers that may be promoting outbreaks of aMWS and the switching of chronic infections to acute lesions. This investigation of aMWS is described over four chapters. First, the bacterial communities between healthy and diseased M. capitata colonies were compared during an ongoing aMWS outbreak versus a non-outbreak period to identify whether a specific shift in bacterial community structure is associated with this disease. The bacterial communities were analyzed using high-throughput sequencing and all health states shared different community compositions with an overall high abundance of Escherichia spp. possibly originating from sewage contamination. Second, a coral disease treatment method was assessed to determine whether the removal of cMWS lesions from M. capitata colonies could reduce morbidity and prevent re-infections. The treatment resulted in an overall reduction in morbidity and prevented lesions from switching from chronic to acute tissue loss. Third, to further describe potential causative agents of this disease, bacterial isolates from diseased M. capitata were screened for virulence using controlled infection experiments. Isolate OCN003 was identified as an etiological agent of aMWS, and more readily infected cMWS-afflicted coral fragments than healthy fragments, which is the first coral pathogen demonstrated to act as a secondary pathogen. Lastly, OCN003 genome was sequenced and was identified as a novel bacterial species and named Pseudoalteromonas piratica.
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