Dynamics of Zooplankton-Mediated Disease Outbreak in Coral-reef

Coral diseases have been identified as one of the leading causes of the collapse of coral reefs worldwide. Coral reefs worldwide are facing severe stress due to the increase in disease outbreaks. Yet the mechanisms of coral disease are poorly understood. To study the role of zooplankton in the transmission of White Band Disease (WBD) in corals, we propose a five-dimensional non-linear (ODE), eco-epidemiological model under the assumption that the transmission of WBD occurs through contagious and non-contagious pathways. The WBD is assumed to be transmitted due to the exposure of corals to zooplankton and the presence of free-living pathogens in the environment apart from the presence of infected corals. The WBD is assumed to propagate following nonlinear incidence. We also assume that a fraction of the microscopic phytoplankton (zooxanthellae) population plays mutualism with the corals. We perform equilibrium and stability analysis of the system and found that the system undergoes a Hopf bifurcation when the WBD transmission rates exceed some critical threshold leading to oscillatory dynamics that can drive the coral population to extinction. We found that zooplankton-mediated transmission of coral disease is highly detrimental to corals compared to the other modes of disease transmission, while infected coral-mediated disease transmission is least detrimental to corals. We also observe that increase in the mutualism between phytoplankton and susceptible corals helps in recovering the coral population. Computer simulations have been carried out to illustrate different analytical results.