Epidemiological computer models have classically consisted of portions of the population, or “compartments,” that are grouped according to general categories such as infected, susceptible, and immune. These classic models make many assumptions about the population in question including that the compartments are composed of completely homogenous groups of individuals. The real world is not as simple, and individuals have varying rates of susceptibility and recovery.  Here, the advantage of agent-based models becomes important most especially in the context of a coral reef.  Most of the diseases affecting reefs today are found to afflict more than just one species. Life history characteristics are variable across coral species that could have a considerable influence on their subsequent rates of susceptibility and recovery.  In a classical epidemiological model, differences are ignored while an agent-based model incorporates variability into individuals. 

Initially, the model will be developed with existing information. Through the construction of the model, key information that is lacking will be identified and can then be collected through field studies. The information gained through this field study can then be used to help calibrate the model. A representation of a hypothetical epizootiological model of coral disease based on known data and calibrated with field data is shown in Figure 1.

Figure 1. A simulated example of a hypothetical reef consisting of four different 
species.

Figure 1 is consistent with the nature of an agent-based model, all of the individual coral heads would contain differing life history, susceptibility, and recovery rates depending on their species and history.  More consistent with a real reef, this “mock-reef” contains a heterogeneous collection of coral colonies.  A coral disease could be introduced that infects first one coral. Diseased corals are represented by red individuals and changes represent the progression of the disease through the coral reef ecosystem. Corals that have experienced total mortality are taken out of the system (represented by the empty containers) while corals that have experienced recovery remain alive (orange individuals).

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