Diseases of marine organisms have emerged as a serious problem contributing to the decline of coral reef resources worldwide. Loss of coral reef habitats carry social and economic implications especially in island states, such as Hawaii, which depend on reefs for food, shoreline protection and tourism. Our ability to manage coral diseases is hampered by a lack of knowledge of which environmental variables affect disease, mechanisms of host defense, and the etiology of most of the numerous described coral diseases. The PIs of this project discovered a coral disease system that can be used as a model to explore many components of the host-environment-pathogen triangle of disease causation. Montipora white syndrome (MWS) is an infectious disease that results in progressive tissue loss on colonies of Montipora capitata, and has been found on reefs throughout the Hawaiian archipelago. It is particularly prevalent in Kaneohe Bay, Oahu, which has a long history of reduced water quality, and this suboptimal environment sets the stage where host-pathogen interactions occur. In Kaneohe Bay, M. capitata is a major reef-building species, and is found in two color morphs (red and orange) that harbor different clades of zooxanthellae. During preliminary surveys, the PIs discovered intraspecific variability in response to MWS between color morphs. Although the red morph was dominant within survey transects (80% of the colonies), the orange morph was disproportionately affected by MWS (70% of the affected colonies). Microbial studies found a shift in bacterial communities on MWS-affected and healthy M. capitata and allowed identification of potential pathogens. Numerous bacterial strains were cultured and screened for pathogenicity and three strains, which produced lesions, were identified as potential pathogens. Two of the putative pathogens (Vibrio spp.) produced diffuse tissue whereas the other bacterial strain (Pseudoalteromonas sp.) produced acute tissue loss.
In the field, the PIs also observed two patterns of tissue loss on M. capitata; a slow, chronic pattern of tissue loss, which they followed through time with tagged colonies (chronic MWS), but also a rapid onset of acute tissue loss (acute MWS). Thus they discovered an infectious coral disease that results in significant coral mortality that has the unique component of differences in disease susceptibility among color morphs. The PIs identified three potential bacterial pathogens that will be used to investigate underlying factors affecting the coral-environment-pathogen triad of disease causation. The Hawaii Institute of Marine Biology (HIMB) is located within Kaneohe Bay allowing year-round access to reefs for research on Montipora white syndrome. The goal of this project is to investigate the host- environment-pathogen triangle of disease causation for Montipora white syndrome. The objectives of this research will be to: 1) investigate mechanisms contributing to differential disease resistance in red (less susceptible) vs. orange (more susceptible) morphs of M. capitata. The PIs will compare antimicrobial activity in the holobiont, mucus and mucus-associated bacteria of the two color morphs of M. capitata, and will compare the natural coral-associated microbial flora between the two color morphs; 2) use manipulative aquarium studies to determine whether environmental stressors (elevated temperature, nutrient stress) differentially affect the progression or transmission efficiency of MWS in red vs. orange morphs of M. capitata; 3) use challenge experiments to confirm the role of bacterial pathogens as causative agents of MWS, and to determine the response of red vs. orange morphs of M. capitata to three putative pathogens. This project will involve a multidisciplinary team to provide a broader perspective of coral disease processes. This will be the first comprehensive study conducted on a coral disease in Hawaii.
Broader impacts and integration of research/education will consist of multidisciplinary, hands-on research experiences for graduate and undergraduate students from the University of Hawaii and the University of Mississippi. Both universities have diverse student bodies and large complements of minority students. The UM graduate student will also have the opportunity to contribute to the fieldwork in Hawaii. Information from this project will be integrated into general biology classes at UH West Oahu and microbiology classes at UH Manoa, both of which serve native Hawaiians and Pacific Islanders. This project will provide opportunities for undergraduate students from Pacific Islands to experience research through the Undergraduate Research Mentoring (URM) program sponsored at UH. K-12 education will include integration of these results into classes for high school students participating in the PaCES/B-WET Summer Environmental Science Program for high school students coordinated through HIMB each summer. It will also be used for training students through the He'e Nalu, an environmental science program for at-risk youth. In Mississippi, the public will be informed through the Central Gulf of Mexico Center for Ocean Sciences Education Excellence (COSEE) and J.L. Scott Marine Education Center.
Coral reefs worldwide have been declining at an alarming rate, and over 1/3 of the world’s corals are now listed as threatened. Local anthropogenic stressors, combined with global climate change, 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; Figure 1). MWS occurs in two forms, a chronic slowly -progressing form, and an acute form that occurs in periodic outbreaks. Altogether, 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 (Figure 2), and we discovered that the orange morph is affected by disease more frequently than the red morph. 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 coral’s 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 coral’s immune systems may differ among the color morphs, and this may help explain why the red morphs 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 due to changing climatic conditions, it is crucial that the next generation of marine biologists is trained in disease investigation. 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.
