Temperature affects coral disease resistance and pathogen growth

Temperature anomalies on coral reefs now routinely exceed coral stress thresholds, making temperature a critical variable to consider in coral host-pathogen systems. While temperature is widely hypothesized to drive coral disease outbreaks by decreasing coral resistance and increasing pathogen growth rates, tests of the temperature hypothesis are rare. Here we report evidence from the sea fan coral Gorgonia ventalina-Aspergillus host-pathogen system that temperature stress increases one component of sea fan resistance. Experimentally infecting sea fan fragments while increasing temperatures to reflect summertime highs in the Florida Keys, USA, caused a 176% increase in activity of host-derived antifungal compounds. Thus, temperature stress and infection induce higher levels of resistance. However, pathogen growth rate also increases over the same temperature range, providing an opportunity for pathogen establishment before host resistance is maximal. This dual effect of temperature emphasizes the need to test intact host-pathogen systems. Given predictions for future warming events, aspergillosis is predicted to continue causing sea fan mortality in the Caribbean Sea.