Population- and temperature-dependent variation in molt phenology and disease susceptibility shape epidemiological outcomes in American lobster ( <i>Homarus americanus</i> )

Abstract Disease and climate change are among the stressors influencing the American lobster fishery, with impacts varying across the species’ geographic range. Increasing seawater temperatures, due to climate change, synergistically alters epizootic shell disease (ESD) epidemiology and molt phenology of the American lobster; however, it is unclear if lobster populations differ in how seawater temperature impacts these responses. This study examined the interactive effects of water temperature, regional lobster population, and molt status on ESD through a 141-day controlled common garden experiment. Lobsters sourced from the Gulf of Maine (Casco Bay, Maine) and Southern New England (Buzzards Bay, Massachusetts and Niantic Bay, Connecticut) were exposed to either a cold-water treatment (13°C, associated with low ESD prevalence) or a warm-water treatment (20°C, associated with high ESD prevalence and severity). Lobsters from the Gulf of Maine were more susceptible to ESD than both Southern New England populations. Warmer water increased both prevalence and severity of ESD but also increased molting (out of diseased and damaged exoskeletons), particularly in the lobster population from Casco Bay, Maine. This study is the first to account for molt stage of American lobsters, highlights population level differences in ESD onset and progression relative to temperature, and increases our understanding of how water temperature, source population, and molt phenology can interact to alter the epidemiology of ESD on the American lobster. This information provides managers and industry with population specific metrics for understanding ESD into the future.