Disentangling effects of disease and bleaching on corals by fitting population models to data

Coral diseases have increased in frequency over the past few decades and are known to have major impacts on the structure and composition of coral reef communities. Environmental effects, such as temperature-induced bleaching, are emerging as stressors which can trigger coral disease outbreaks and compromise recovery, but the effects of human impacts are not well understood.  A model of coral disease dynamics was developed and fit to an 8-year data set of coral abundance, disease incidence, and bleaching incidence in the Florida Keys. We compared parameter estimates for disease susceptibility among different coral species and predicted long-term changes in abundance.  Additionally, we explored whether key environmental stressors could explain environmental stochasticity in the data using model selection criteria to compare models.  We found differences among coral species in rates of population growth and susceptibility to disease.  In some species bleaching exacerbated disease susceptibility, but for others it had little effect on population dynamics.  Such species differences lead to long-term changes in coral community composition, but the degree of change depends on the strength and frequency of environmental stressors.