Award: OCE-0961814

Coral reefs worldwide have been declining at an alarming rate, and over 1/3 of the worldÆs corals are now listed as threatened. Local anthropogenic stressors (overfishing, sedimentation, eutrophication), combined with global climate change (increased sea surface temperatures, ocean acidification), have already resulted in significant coral loss, and coral bleaching and disease epidemics are predicted to increase in frequency. Coral disease research is in its infancy, especially in the Indo-Pacific, where baseline surveys have only recently been initiated. Our understanding of why coral disease is emerging as such a widespread problem is rudimentary at best and is severely hampered by our lack of knowledge of mechanisms affecting the coral-environment-pathogen triad of disease causation. In Kaneohe Bay, Oahu, Hawaii, the common reef coral, Montipora capitata, is affected by a progressive tissue loss disease called Montipora white syndrome (MWS). MWS is causing significant mortality to M. capitata and a shift in the overall community structure on affected Hawaiian reefs. M. capitata occurs in two color morphs, red and orange, and we discovered that the orange morph is affected by disease more frequently than the red morph. Why? Our research brought together a multidisciplinary research team, with expertise in complementary areas, to investigate the underlying mechanisms contributing to differential resistance to MWS in red (less susceptible) vs. orange (more susceptible) morphs of Montipora capitata. Through our research we have discovered three bacterial pathogens that can cause tissue loss in these corals. Although both red and orange corals can become infected with these bacteria, the orange morphs were more easily infected. Corals protect themselves from bacterial diseases through a number of defenses, including the production of antimicrobial chemicals. In addition, the coralÆs own normal bacterial flora can also help keep the pathogens at bay. We found that the red and orange morphs of M. capitata had significant differences in their antimicrobial activity and the composition of their normal bacterial community. This suggests that the coralÆs immune systems may differ among the color morphs, and this may help explain why the red morph is more resistant to bacterial infection. Environmental factors can also affect pathogen-host interactions, with stressful conditions making hosts more vulnerable to disease. We examined whether elevated water temperatures (e.g., due to a changing climate) or nutrient contamination affected disease virulence (harm) or rate of transmission (disease transfer from one coral to another). We found no significant effect of either stressor on MWS and will continue to work to understand what component(s) of the environment make the corals in Kaneohe Bay so susceptible to disease. Through our continued research efforts, we hope to understand why coral disease outbreaks are becoming more common so that steps can be taken to stop this downward trend in coral reef health. Due to the frequency with which emerging diseases are currently being described, and the expected increase in stress on coral reefs from changing climatic conditions, it is crucial that the next generation of marine biologists get trained in disease investigations. Through this research we directly trained seven graduate students from the University of Hawaii and the University of Mississippi in techniques required for marine research. Through internships we also exposed 18 undergraduate college students to the wonders and rigors of marine research. New knowledge based on our research was integrated into community presentations and programs such as the Eyes of the Reef network (www.eorhawaii.org) so that the general public can also be informed and on the lookout for changes in the health of our remaining coral reefs. Last Modified: 08/16/2014 Submitted by: Greta Aeby