Effects of epizootic shell disease on egg quality of the American lobster

Abstract

Epizootic shell disease (ESD) of the American lobster, Homarus americanus Milne Edwards, 1837, is of increasing concern, particularly in the southern New England fishery where prevalence is highest. Egg-bearing female lobsters are more susceptible to the disease because many of them molt less frequently when carrying eggs. This study examines the effect of the disease on late-stage embryos through measures of egg quality. Egg samples were taken from ninety lobsters with varying levels of ESD in lower Buzzards Bay and Vineyard Sound off the coast of Massachusetts, USA. Egg quality was measured with biomass (egg area and dry weight) and biochemical (total carbon and total nitrogen) components. Each response variable was estimated using linear mixed-effects models that included potential covariates as measures of maternal adult lobster size and embryonic development. The effect of disease was significant for all of the response variables, indicating that the presence of the disease correlates with individual egg quality. Counterintuitively, results showed that as disease severity increased, measures of egg quality also increased. Trends showed that light cases of ESD produced similar responses to lobsters with no disease present. Moderate and severe levels of the disease also produced similar results. This could suggest that heavily diseased lobsters are exhibiting energetic trade-offs, investing more energy into reproduction. It is also possible that this trend is the result of other combined effects corresponding to lobster molt cycles, spawning timing, and environmental conditions that also result in the presence of ESD. Effects of the disease on early life history processes could be important considerations for future research on ESD and its effect on the lobster population.