Coral Bleaching and Disease: Effects on Threatened Corals and Reefs

Science Center Objects

A severe disease - tentatively named stony coral tissue loss disease - is rapidly killing corals in the U.S. Virgin Islands. Scientists from the U.S. Geological Survey, the University of Puerto Rico, and the National Park Service are working together to better under the disease and determine if the disease affecting corals in the USVI is the same one that has been killing corals in Florida since 2014. 

The Science Issue and Relevance: Severe coral disease is now killing corals in the U.S. Virgin Islands (USVI), including those within Virgin Islands National Park and Virgin Islands Coral Reef National Monument.  This disease, tentatively named stony coral tissue loss disease (SCTLD), may be the same one that started killing corals in Florida in 2014.  First observed in 2019 in St. Thomas, it has now spread throughout almost all areas in St. John, St. Thomas and St. Croix.  Up until this outbreak, the greatest degradation of reefs in the USVI within the last 50 years was associated with white plague disease that followed extensive coral bleaching in 2005. From 2005 to 2007, the amount of living coral cover at long-term sites monitored by USGS and the National Park Service (NPS) declined an average of 60%. With climate change, high seawater temperatures are expected to lead to more frequent bleaching episodes and possibly more disease outbreaks. The anticipated benefits of the marine protected areas (i.e., the national park and national monuments in the USVI) could be undermined by these stressors. 

coral with stony coral tissue loss disease

One of the coral species most susceptible to stony coral tissue loss disease shows active lesions of the disease around St. John. (Public domain)

 

In 2006, Acropora palmata, the primary reef-building species in shallow water throughout the Caribbean, was listed as threatened under the U.S. Endangered Species Act based on losses from disease and major storms.  In 2014, 5 more species, including two Orbicella species that are the most abundant around St. John, were also listed as threatened. Acropora palmata is not known to be affected by SCTLD, but it is estimated that over 90% of the Caribbean population was killed by white band disease. There is a need to better understand the relationship among high seawater temperature, bleaching, and disease. 

 

Methodology for Addressing the Issue: USGS WARC is collaborating with other USGS scientists and partners from the University of Puerto Rico and the NPS to collect samples from diseased and apparently normal coral colonies around St. John and Puerto Rico to determine if the disease observed in these areas is the same as that in Florida. USGS scientists will be relating the appearance of gross lesions to the condition of the tissues when examined with light and electron microscopes, and will continue to monitor and photograph corals around St. John, inside and outside NPS waters, primarily to document the spread of SCTLD and the coral species affected. USGS WARC regularly provides observations to the Virgin Islands Coral Disease website and confers with other experts regarding the spread of SCTLD and how different coral species respond to the disease.  

coral with stony coral tissue loss disease

One of the coral species most susceptible to stony coral tissue loss disease shows active lesions of the disease around St. John. (Public domain)

 

Future Steps: Efforts will be made to sustain sampling and monitoring of sampled corals over time by the University of Puerto Rico and the NPS. Such time series of corals have received very little attention to date. USGS WARC will continue to monitor and photograph diseased and unaffected corals.

 

Related Publications:

Weil E,  Rogers C  (2011)  Coral reef diseases in the Atlantic-Caribbean.  Part 5. pages 465-491. In:  (editors Zvy Dubinsky, Noga Stambler) Coral Reefs: An Ecosystem in Transition.  DOI: 10.1007/978-94-007-014-4_27.

Miller J, Muller E, Rogers C., Waara, R., Atkinson, A., Whelan, K. R. T., et al. (2009). Coral disease following massive bleaching in 2005 causes 60% decline in coral cover on reefs in the US Virgin Islands. Coral Reefs 28, 925–937. doi:10.1007/s00338-009-0531-7.