Laboratory studies on the effect of temperature on epizootic shell disease in the American lobster, Homarus americanus

Epizootic shell disease (ESD) is a persistent threat to the population of American lobsters, Homarus americanus H. Milne-Edwards, 1837, in Long Island Sound and off southern New England, USA. ESD is caused by a bacterial dysbiosis that occurs in association with increased water temperature and exposure to anthropogenic stressors. Temperature is a leading factor driving the severity and incidence of ESD. Our objective was to quantify disease progression and dynamics in relation to host molting and mortality at three rigorously controlled temperatures (6, 12, and 18 °C) over a 5–6-mo period. Lobsters were photographed at various time points and image analysis was used to examine changes in lesion development over time. The disease progressed at all three experimental temperatures, but it had a significantly faster growth rate at 18 °C. Mean progression rates varied from 8.6–10.4 mm² d^–1 at the lower temperatures to >25.6 mm² d^–1 at 18 °C. The mean daily growth rates give conservative estimates for individual progression from light to moderate disease states; i.e., approximately 233 d at 6 °C and 95 d at 18 °C. We show that increased temperature leads to rapid progression of ESD, but individual variation, presumably modulated through immune defenses, can slow the disease and possibly enhance survival of affected lobsters.