Epizootic Shell Disease in the American Lobster (Homarus americanus H. Milne Edwards, 1837)

Epizootic shell disease (ESD) in the American Lobster (Homarus americanus) continues to persist in the waters of southern New England and eastern Long Island Sound, and results in significant mortality and economic harm. The etiological agent of this disease appears to be bacterial. Culture-independent molecular techniques were employed to characterize the bacterial communities that populate the disease lesions and other areas of the lobster cuticle. These include amplicon length heterogeneity and multitag pyrosequencing. This research represents the first attempt to comprehensively survey the lobster carapace microbiome. Statistical analyses of the data have identified several bacteria that are prevalent on the surface of lobsters in different states of health. In particular, principal coordinates analysis (PCO) helped visualize the differences between samples, and discriminant analysis was employed to identify bacteria that correlated with the three states of health: Diseased, Healthy, and Healthy-on-Diseased (unaffected carapace regions on diseased animals). In addition, correlational network analysis was used to understand how these bacteria correlate with each other in the same three states of health, and to identify correlation differences between the states. While some researchers have identified a novel chitinolytic bacterium of the genus Aquimarina (A. 'homaria'), as consistently appearing on lobsters with shell disease, this research found no evidence of correlation of this species with all occurrences of disease. Instead, analysis revealed that the genus Aquimarina was present in all states of health and correlated only weakly with the diseased state. The data suggest that this disease is not caused by a single pathogen, but by a state of dysbiosis where normally occurring microflora emerge as potential opportunistic pathogens when there is some apparent environmental stressor that alters the interaction of the surface biofilm of the lobster.