While conducting unrelated research on human diseases, University of Hawai'i postdoctoral fellow Jamie Caldwell recognized a common experimental design in the medical field for its potential value in addressing a non-human problem she was also researching—coral disease.
In a study published in Scientific Reports, Caldwell and her team used a statistical technique typically employed in human epidemiology to determine the ecological risk factors affecting the prevalence of coral disease. Most diseases in corals are either endemic or epidemic—with no gray area, it can be challenging for researchers to understand how disease spreads.
“Coral diseases are pretty rare,” Caldwell told Laboratory Equipment. “When there's not an outbreak, we might see 1 in 10,000 colonies infected. And they occur across a huge geographic area, so the chance of observing disease is low.
The rarity of disease combined with the sheer number of coral communities combine to increase the difficulty of assessing the marine life. Models end up incorporating so many healthy colonies that the rare, diseased colonies are not properly identified as such. However, the statistical technique Caldwell employed solved this problem by allowing the researchers to focus the large dataset on pairs of healthy and disease colonies.
The team then compared biological, environmental, human-related, and physical disease drivers to better isolate the ecological conditions that drive disease. They found larger corals had higher disease risk overall. In particular, growth anomalies were more common in reefs with fewer fish, limited water motion and in areas adjacent to watersheds with high fertilizer and pesticide runoff. White syndrome, a disease that results in coral degradation from base to tip, was associated with wave exposure, stream exposure, depth and cooler ocean temperature.
“We found disease was more common near agriculture, golf courses and steam mouths, particularly in locations with limited water flow, like embayments. This suggests we should limit land-based runoff as much as possible, especially near places that use pesticides and fertilizers,” Caldwell said of the study results.
Identifying the conditions associated with higher disease risk in coral improves researchers’ abilities to predict future outbreaks in the future and in new locations, especially when factoring in seasonal temperature predictions for specific regions.
For example, over the next two years, Caldwell and her colleagues will develop seasonal and near real-time forecasts of coral disease outbreak risk for all U.S.-affiliated Pacific Islands and the Great Barrier Reef. The forecasts, funded by NASA, will be publicly available through NOAA Coral Reef Watch.
Photo: Jamie Caldwell conducting a coral health survey. Credit: University of Hawaii - HIMB