Supplementary material from "Changes in Transmission Rates Drive Seasonal Patterns of Shrimp Black Gill Disease"

Quantifying the processes affecting disease dynamics is critical for informing management strategies. We present the results of a series of experiments and mechanistic models that disentangle the roles of disease transmission and host density, mortality, and recovery in driving seasonal prevalence of shrimp Black Gill (sBG) disease. We first quantified seasonal sBG transmission to uninfected hosts deployed into the environment. Next, we manipulated temperature and infection status in a laboratory experiment to quantify drivers of host mortality and recovery. Finally, we utilized these experiments to parameterize a series of mechanistic models to determine if disease dynamics were driven by host density-dependent or independent factors. Transmission was highest during the summer, with 75-91% of hosts acquiring infection, but declined substantially in all other seasons (0-10%). In our lab experiment, we observed little disease-induced mortality and complete recovery from infection in all treatments. Our models revealed that host density did not drive disease dynamics. Together, this suggests that high transmission rates in the summer caused by seasonal changes in the environment, followed by gradual recovery when transmission rates are low causes variation in sBG prevalence. Our methodology provides a framework to quantify drivers of seasonal variation in disease prevalence in fisheries.