Deadly coral disease can be transported in ship hulls

Stony coral tissue loss disease (SCTLD) – a disease caused by a bacterial pathogen that can be transmitted via direct contact or through the water column – was first detected near Miami in 2014 and has since spread throughout all Florida’s coral reef, as well as into the Caribbean, including waters off Belize, Jamaica, St. Maarten, and the U.S. Virgin Islands. A recent study led by the University of Miami (UM) suggests that transport through ship hulls, where the vessels take on ballast water from one region to keep it stable and release it at a different port, may have contributed to the spread of this deadly coral disease.

“Outbreaks in very distant locations suggests that disease transport was aided by means other than just ocean currents, such as through ship ballast water,” said study lead author Michael Studivan, an expert in Marine and Atmospheric Sciences at UM.

To test this hypothesis, the researchers conducted two disease transmission experiments in the university’s lab. In the first experiment, they exposed healthy corals to three types of water: disease-exposed, disease-exposed but UV-treated, and non-disease-exposed. During a period of six weeks, they observed the onset of disease symptoms and mortality to assess how many corals became infected, how quickly, and whether UV treatments of disease-exposed water resulted in fewer affected corals. Then, in another experiment, the scientists held the same type of water in containers for one to five days, in order to simulate a ship’s ballast tank, and exposed healthy corals to the water to verify whether SCTLD pathogens could survive over time, and whether they became more or less contagious over time.

The experiments revealed that, although UV treatment of disease-exposed water led to a 50 percent decrease in the number of corals exhibiting disease symptoms, unfortunately the statistical risk of transmission and volume of water needed to elicit SCTLD lesions remained similar to untreated disease-exposed water. Moreover, the ballast hold time (one versus five days) did not seem to have a significant effect on the onset of disease. Thus, results from both experiments provide evidence that the SCTLD pathogens can persist in both untreated and UV-treated ballast water and remain pathogenic.

“The results suggest that ship’s ballast water poses a threat to continued spread and persistence of SCTLD throughout the Caribbean and potentially to reefs in the Pacific, and that established treatment and testing standards may not mitigate the risk of disease spread,” Studivan concluded.

The study is published in the journal Nature Scientific Reports.

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By Andrei Ionescu, Earth.com Staff Writer