Investigation of Microbiota Associated with Rapid Tissue Loss in Captive Indo-Pacific Corals

Abstract

Many factors are known to contribute to the unprecedented decline of coral reefs, with rapid declines resulting from coral diseases. The occurrence of coral disease in closely monitored and controlled environments offers a unique opportunity to study such events. In 2011, select corals in the Smithsonian’s National Museum of Natural History Indo-Pacific coral-reef aquarium underwent rapid tissue loss in 24–48 hours. Initial results indicated the presence of Gram-negative bacteria, similar to Rickettsia-like organisms (RLOs) previously observed in Caribbean corals. From 2016–2018, additional samples were collected from both diseased and apparently healthy corals for histopathological and transmission electron microscopy (TEM) examination. The samples revealed interactions between RLOs and host corals, both when corals were apparently healthy and when they were diseased, i.e., losing tissue. Corresponding environmental data were analyzed to determine if environmental parameters influenced disease outbreaks in this system. It remains unclear what environmental factors contributed to disease outbreaks in this system; however, this is the first study to attempt to analyze a combination of water quality parameters in tropical coral-reef aquariums to determine if any may be contributing factors to coral disease outbreaks. Associated organisms were present in subsamples of both apparently healthy and diseased corals, with evidence suggesting they may play a role in transmission of RLOs. Statistically significant linear relationships emerged between condition parameters in apparently healthy and diseased corals. This is the first study to histologically examine the role of RLOs in multiple Indo-Pacific coral species and explore the possible transmission of disease in a recirculating coral reef system.