A team of international researchers used a statistical technique typically employed in human epidemiology to determine the ecological risk factors affecting two coral diseases—growth anomalies, abnormalities like coral tumors, and white syndromes, infectious diseases similar to flesh eating bacteria. The study, led by University of Hawaiʻi at Mānoa Hawaiʻi Institute of Marine Biology (HIMB) postdoctoral fellow Jamie Caldwell, was published in Scientific Reports in February.
“This study provides information about what specific conditions impact coral health and the results could be used to help improve coastal development plans by considering the downstream effects of different land-use types on the coral community,” said Caldwell. “Additionally, this improves our ability to predict future outbreaks based on environmental conditions and mitigate disease drivers like runoff from golf courses to evade outbreaks altogether.”
Healthy coral reefs are culturally important ecosystems and vital to Hawaiʻi’s tourism industry. Disease outbreaks can wreak havoc on coral ecosystems. Because some diseases are rare and hard to observe, it had been difficult to rigorously make inferences about which disease drivers were most impactful.
What drives disease?
The team compared biological, environmental, human-related and physical disease drivers with observations of healthy and diseased coral colonies.
“We specifically looked at associations between disease occurrence during non-outbreak periods to understand what conditions allow diseases to persist in the environment at low levels year-round, or in between epidemics,” said Caldwell.
They found larger corals had a 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. In contrast, white syndromes were associated with wave exposure, stream exposure, depth and cooler ocean temperature.
“The methods we used in this study highlight the power of the experimental design common in epidemiology but rarely, if ever, used in ecological studies,” said Megan Donahue, co-author and HIMB associate researcher.
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