Dynamics and impact of the coral disease white plague: insights from a simulation model

Coral disease is playing a significant role in structuring today's coral reef communities. While monitoring programs document declines associated with coral disease, there is a lack of tools that can test hypotheses of disease incidence and control. Here, we describe a modeling tool developed to test hypotheses about the spread and impact of white plague disease in diverse coral populations distributed across heterogeneous reef landscapes. The model Simulation of Infected Corals (SICO) was based on the dynamics of white plague over the course of 6 yr of monitoring on the fore-reefs of Little Cayman (Cayman Islands, British West Indies). A pattern-oriented modeling approach using a genetic algorithm was used to calibrate model parameters that describe disease introduction, transmissibility, and host susceptibility. Simulation patterns most accurately reflected patterns observed at study sites when disease was introduced at regular intervals and was transmissible within a limited area. Projecting forward in time, coral cover tended to drop precipitously until colonies were so sparse that disease transmission among colonies was rare. A sensitivity analysis of disease parameters indicated that the effect of changing disease parameters depended on the type of coral community, but that in communities dominated by susceptible species, local preventative measures were generally more effective than treatment measures in limiting disease impact.