Effects of epizootic shell disease in American lobster Homarus americanus determined using a quantitative disease index

Abstract

The incidence of epizootic shell disease in American lobster Homarus americanus has increased in southern New England, USA, in the last decade, but few longitudinal studies have followed the disease progress in individual lobsters or demonstrated direct effects on mortality or growth. Diseased lobsters were held in the laboratory for 1 yr, and the progression of disease and its effects on molting, mortality, and growth were monitored. A quantitative disease index (QDI) was developed by measuring disease lesions in digital images of the carapace and expressing the result as a proportion of shell area. Some lobsters died due to high temperatures, but at least 13 of 55 lobsters (24%) died as a direct result of disease-related problems, mostly during molting, and there was a significant relationship between mortality and high values of the QDI. Lobsters that molted successfully were free of disease lesions, but many had exoskeletal deformities. There was no relationship between pre-molt size and disease severity, but molt increment was significantly correlated with premolt carapace length (CL) and negatively correlated with QDI. However, percentage growth was negatively correlated with QDI, but not with pre-molt CL. These significant lethal and sublethal effects of epizootic shell disease should be considered in lobster management.

Epizootic shell disease in American lobsters Homarus americanus in southern New England: past, present and future

“…The relationship between young-of-the-year and pre-recruit abundance changed dramatically in 1996 (Wahle et al 2009), weakening the relationship between the stages and indicating an increased rate of mortality. Stevens (2009) also found evidence for increased mortality in the laboratory during molting due to complications of ESD.…”

“…As temperature also affects growth rates and size at maturity, the interplay between the endocrine system, environmental factors and disease becomes complex. Castro et al (2006) documented decreases in growth increment associated with shell disease from tagging studies, subsequently demonstrated by Stevens (2009) in the laboratory. Inadequate nutrition was also implicated in a paper by Tlusty et al (2008), suggesting that lobster health and condition was compromised during chronic feeding of herring.…”

Diseases of American lobsters (Homarus americanus): A review

“…Additional to the multifactorial nature of shell disease, diseased lobsters are immunodeficient and have lower exoskeleton defences (Allam et al 2009). Based on the innovative tools of a regional disease index and a quantitative disease index, Stevens (2009) clearly demonstrated that epidemic shell disease has significant lethal and sublethal effects. The latter likely results from lower growth rates due to stress of disease.…”

Gene Expression in American Lobster (Homarus americanus) with Epizootic Shell Disease

“…Epizootic shell disease (ESD) is a syndrome associated with the progressive development of irregular, deep lesions on the carapace (Smolowitz et al 2002. Lobsters with signs of ESD exhibit increased mortality in captivity and sublethal effects on growth , Stevens 2009). The high incidence of ESD in southern New England (SNE) has been suggested as a possible causative factor in the observed decline in the SNE lobster stock since 2001 (Howell 2012).…”