Research Projects 2014-2016

Maintaining healthy coastal ecosystems: Understanding disease risk of Hawaiʻi’s coral reefs and sources of coral pathogens

PRINCIPAL INVESTIGATOR: Sean Callahan
Co-INVESTIGATORS: Greta Aeby
Graduate Trainee: Amanda Shore

A large outcrop of coral shows nearly half discolored a distinct white
Hawaiian coral shows the effects of Montipora White Syndrome, a disease spreading through Kauaʻi corals.

Disease is an emerging problem to coral reef ecosystems worldwide. Yet, the basic mechanisms of disease in corals are poorly understood. For infectious diseases, vectors allow the spread of pathogens, and environmental stressors reduce the host’s ability to defend against invading pathogens. Identifying sources of coral pathogens and understanding environmental risk factors are important for predicting and mitigating disease outbreaks. Montipora White Syndrome (MWS) is a coral disease in Hawai’i known to be caused by bacterial infections. Seawater, terrestrial freshwater/sediment, and marine organisms in Kāne‘ohe Bay were sampled and tested for the bacterial pathogens. In addition, stress experiments were conducted to determine if decreased salinity or sedimentation lowered coral defenses to pathogen invasion. Lastly, field surveys were conducted to determine which reefs around Oahu were at risk of developing disease. Coral pathogens were identified from stream water, seawater, and several marine organisms, including the coral host (Montipora capitata). Stress tests showed that decreased salinity (but not sediment stress) allowed disease to occur with a lower dose of bacterial pathogen. Reefs in the Central and Southern region of Kāne‘ohe Bay and reefs along the North Shore of Oʻahu were identified as at risk of developing MWS. With the presence of coral pathogens in multiple sources, it is likely that corals have frequent exposure to bacterial pathogens. Additionally, stressors like reduced salinity during rain events may allow pathogens to invade coral more easily, leading to disease outbreaks. This research highlights the importance of maintaining healthy water sheds in order to maintain healthy coastal ecosystems.