Ocean temperature anomalies as a driver of coral disease outbreaks

Disease outbreaks are a major cause of recent mass-coral mortality events. New evidence indicates that anomalously high temperature is an important driver of coral epidemics. Two studies combined ocean temperature data derived from NOAA satellites with in situ surveys of coral disease prevalence to test the temperature- disease hypothesis at regional scales. The first case study asked whether the frequency of temperature anomalies was positively related to White Syndrome (WS) prevalence across 1,500 km of Australia's Great Barrier Reef between 1998 and 2004. The study found a highly significant effect of temperature that was unexpectedly dependent on coral cover; WS outbreaks followed warm years but only on high coral cover (> 50%) reefs, suggesting an important role of host density as a threshold for outbreaks. The second study examined the relationship between Caribbean Yellow Band Syndrome (YBS) dynamics and anomalously high temperatures from 2001-2005. Results indicate that warmer than usual temperatures substantially increased rates of within and among colony disease spread. Additionally, YBS severity followed seasonal water temperature cycles through 2004, with outbreaks and high rates of tissue loss corresponding with high late summer temperatures. Since 2004, disease signs have been persistent throughout the year in most colonies, possibly due to increased minimum temperatures throughout the year. Overall, available results indicate that the frequency of temperature anomalies, which is predicted to increase in most tropical oceans, can increase the severity of coral disease outbreaks, leading to mass coral mortality, changes in community structure, and the loss of reef habitat.