Deadly coral disease in Florida, Caribbean may be transported in ship hulls, study finds

Stony coral tissue loss disease, or SCTLD, was first observed near Miami in 2014 and has since spread throughout all of Florida's Coral Reef and into the Caribbean, including in waters off Jamaica, St. Maarten, U.S. Virgin Islands, and Belize.

Researchers suggest that transport through ship hulls, where the vessel take on ballast water in one region to keep it stable and release it at a different port, may have contributed to disease spread.

"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 the study's lead author Michael Studivan, an assistant scientist at the UM Cooperative Institute for Marine and Atmospheric Studies (CIMAS) and NOAA's Atlantic Oceanographic and Meteorological Laboratory.

The UM Rosenstiel School researchers conducted two disease transmission experiments in the Experimental Reef Lab at the Rosenstiel School of simulated ship's ballast water and UV treatment of ballast water to determine whether SCTLD pathogens can be transported in this manner, and whether established ballast water treatment approaches like UV can successfully prevent spread of disease.

The first experiment exposed healthy corals to three types of water: 1) disease-exposed, 2) disease-exposed and UV-treated, and 3) non-disease-exposed water in a flow-through tank system. Over a six-week period, they observed the onset of disease lesions and mortality to determine the number of corals that became diseased, how quickly, and whether UV treatment of disease-exposed water resulted in fewer affected corals. In a second experiment, the researchers held the same types of water in containers to simulate a ship's ballast tank for one and five days, then exposed the water to healthy corals to determine if the SCTLD pathogens could survive over time, and whether they became more or less infectious over time.

The researchers then tested the ballast water generated for both experiments in collaboration with the U.S. Naval Research Laboratory in Key West to quantify the microbial communities and their abundance in untreated and treated ballast water.

"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," said Studivan.

The Experimental Reef Lab was designed and built by NOAA's Atlantic Oceanographic and Meteorological Laboratory (AOML) and CIMAS at the Rosenstiel School for conducting research on coral response to changing environmental conditions.

The study's authors include Michael Studivan, Michelle Baptist, Nash Soderberg, Ewelina Rubin from CIMAS; Ian Enochs from AOML; Vanessa Molina and Scott Riley from Excet, Inc., Matthew First from the U.S. Naval Research Laboratory; and Ashley Rossin and Daniel M. Holstein from Louisiana State University.

The research study was supported by EPA agreement (#DW-017-92527801), NOAA Coral Reef Conservation Program (#31252), NOAA OAR 'Omics Program, the Louisiana Board of Regents Research Support Fund Research Competitiveness Subprogram (#LEQSF(2020-23)-RD-A-06) and the National Science Foundation Ecology and Evolution of Infectious Disease (#2109622).