Coral Bleaching and Disease: Effects on Threatened Corals and Reefs

Science Center Objects

Severe coral bleaching in 2005, followed by a disease outbreak, resulted in severe reef degradation in the US Virgin Islands; the amount of living coral cover at long-term monitoring sites decreased an average of 60%. With climate change, high seawater temperatures are expected to lead to more frequent bleaching episodes and possibly more disease outbreaks. 

Coral Bleaching and Disease: Effects on Threatened Corals and Reefs

A colony of the threatened species A. palmata showing signs of white pox disease.

The Science Issue and Relevance: Severe coral bleaching in 2005, followed by an outbreak of disease, caused greater degradation of reefs within Virgin Islands National Park (and elsewhere in the US Virgin Islands) than any other stressors over the park’s 50 year history. The amount of living coral cover at long-term sites monitored by USGS and NPS declined an average of 60%. Almost all coral species were affected, including the major architects of the reefs, elkhorn coral (Acropora palmata) and star coral (Orbicella annularis). 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 (the national park and national monuments in the US Virgin Islands) could be undermined by these stressors. In 2006, Acropora palmata, the primary reef-building species in shallow water throughout the Caribbean, was listed as threatened under the US 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. Climate change will lead to increasing seawater temperatures and more bleaching episodes. There is a need to better understand the relationship among high seawater temperature, bleaching, and disease.

Methodology for Addressing the Issue: USGS scientists are collaborating with other scientists to synthesize existing information on the relationship among thermal stress and coral diseases and seeking funding for additional research on this important topic. The US Environmental Protection Agency (EPA) has a team of experts, including USGS scientist Dr. Caroline Rogers, who are exploring the feasibility of applying EPA’s Biological Condition Gradient (BCG), first applied to freshwater streams, to coral reefs. Dr. Rogers has been contracted individually to examine specifically the use of this approach for assessing coral condition, primarily diseases.

Coral Bleaching and Disease: Effects on Threatened Corals and Reefs

White plague disease caused major coral mortality following bleaching in 2005.

Future Steps: Funding is being sought to further explore the relationship between high sea water temperatures, bleaching and diseases. Specifically, we are hoping to collaborate further with other researchers including Dr. Erinn Muller who based some of her PhD dissertation on data collected on corals around St. John while working with USGS from 2004 through 2006. 

Publications:

Jackson J et al. (2014)---C Rogers one of many authors in Part 1. Overview and synthesis for the wider Caribbean region (18th of 90 authors) and one of many authors in Part 2. Reports for individual countries and territories (US Virgin Islands) In: Jackson JBC, Donovan MK, Cramer KL, Lam VV (editors) Status and trends of Caribbean coral reefs: 1970-2012. Global Coral Reef Monitoring Network, IUCN, Gland Switzerland. 305 pp