| Over the past four decades, outbreaks of coral diseases have resulted in considerable loss of live-coral cover throughout the Caribbean region. Despite their long histories and ubiquitous distributions, the etiologies of most coral diseases remain poorly understood. Coral diseases has been assumed to be the result of infectious and contagious pathogens, yet recent evidence suggests that some diseases may result from immunocompromised corals that have been subjected to increased stresses associated with climate change. The objectives of this study were to: (1) test waterborne and direct-contact transmission of Caribbean-coral diseases, (2) determine whether signs of coral diseases cluster (< 10m scale) and follow a contagious-disease model, and (3) examine the relationship between thermal stress and the prevalence of coral diseases.;First, results of laboratory-based transmission experiments failed to indicate waterborne or direct-contact transmission, for dark-spot syndrome or yellow-band disease. Second, results of in situ disease mapping revealed no consistent patterns of spatial clustering of any disease that was examined. Third, the relationship between temperature and outbreaks of white-band disease over the last two decades was hindcasted using historical-disease data and remotely-sensed temperature records. White-band disease on A. palmata was best predicted by the 30-year rate of change in seawater temperature, the seasonal minimum temperature, and water depth. The best predictors of the disease on A. cervicornis were the contemporary rate of change in seawater temperature, the seasonal maximum temperature, and the seasonal minimum temperature. These results indicate that both long-term climate-driven changes in sea-surface temperature, and more recent thermal anomalies, have played a significant role in the spread of white-band disease, and the subsequent decline of acroporid corals in the Caribbean.;In conclusion, the research described in this dissertation suggests that many common coral diseases in the Caribbean are not readily contagious. Instead, outbreaks of these diseases are likely the result of opportunistic infections, which occur when the corals' innate immune systems are compromised, particularly under thermal stress. The frequency of thermal-stress events, long-term rates of change in sea-surface temperature, and the breach of thermal maxima, all increase the risk and the likelihood of coral disease on Caribbean reefs. |
