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Assessing the Effects of Disease and Bleaching on Florida Keys Corals by Fitting Population Models to Data
Citation:
YEE, S. H., D. L. SANTAVY, AND M. G. BARRON. Assessing the Effects of Disease and Bleaching on Florida Keys Corals by Fitting Population Models to Data. ECOLOGICAL MODELLING. Elsevier Science BV, Amsterdam, Netherlands, 222(7):1323-1332, (2011).
Impact/Purpose:
In this article we develop quantitative population models to assess the relative impacts of disease, bleaching, and anthropogenic stressors on coral populations. Models are also used to predict the persistence of coral populations under environmental stress. Such models are a critical need under EPA's Ecological Services Research Program. The information in this paper will facilitate the development of models to predict the sustainability of coral reef ecosystems.
Description:
Coral diseases have increased in frequency over the past few decades and have important influences on the structure and composition of coral reef communities. However, there is limited information on the etiologies of many coral diseases, and pathways via which coral diseases are acquired and transmitted are still in question. Furthermore, it is difficult to assess the impacts of disease on coral populations because outbreaks often co-occur with temperature-induced bleaching and anthropogenic stressors. We developed spatially-explicit population models of coral disease and bleaching dynamics to quantify the impact of six common diseases on Florida Keys corals, including aspergillosis, dark spots, white band, white plague, white patch, and yellow band. Models were fit to an 8-year data set of coral abundance, disease prevalence, and bleaching prevalence. Model selection was used to assess alternative pathways for disease transmission, and the influence of environmental stressors, including sea temperature and human population density, on disease prevalence and coral mortality. Classic disease transmission from contagious to susceptible colonies provided the best model only for aspergillosis. For other diseases, direct transmission from the external environment provided the best fit to observed data. Estimates of disease reproductive ratio values (R0) were less than one for each disease, indicating coral colonies were below densities required for diseases to become established through contagious spread alone. Disease outbreaks were typically associated with greater susceptibility of bleached colonies. Projections of winning models indicated that, although disease and bleaching can have substantial impacts on populations, continuing scleractinian coral decline in the Florida Keys appears to be attributable to other stressors. By applying epidemiological models to field data, our study gives qualitative insights into the dynamics of coral diseases, relative stressor impacts, and directions for future research.