Epizootic shell disease (ESD) is an emerging disease in American lobster, Homarus americanus, in southern New England (SNE). Monitoring surveys and research projects have been able to identify the initiation of the disease and changing prevalence levels over spatial and temporal landscapes, including demography. The sudden onset of ESD during the late 1990s was centered in SNE, specifically southern Massachusetts and Rhode Island, which have continued to show sustained mediumhigh prevalence levels. Legal and sublegal lobsters are both affected and we can now show that the disease occurs in small juvenile lobsters. Severity indices show little variation over time but ovigerous females have the highest prevalence and severity. Herein, we summarize available information on ESD in SNE.

The emergence of epizootic shell disease in the American lobster (Homarus americanus) has been devastating to the fishing industry in southern New England. In response, research was initiated to understand the roles of the environment, pathogens, and pollutants in the ecology and etiology of the disease. A comprehensive project was initiated in which tissues and hemolymph from 100 lobsters were collected from an endemic area of disease, Narragansett Bay, RI. The project has moved forward with the purpose of compiling, synthesizing, and propagating the findings from the “100 Lobsters” Project. The resulting tissue bank and Web-based data repository and instructional tools serve as a nascent demonstration project to both the scientific community working on this disease as well as to members of the lobster industry.

The emergence of epizootic shell disease in the American lobster (Homarus americanus) has been devastating to the industry in the coastal waters of southern New England. A comprehensive assessment of the disease syndrome, known as the “100 Lobsters” Project, was initiated to examine health and physiological parameters among laboratories involved in the research on lobster shell disease. A histological study of the 100 lobsters was undertaken as part of that assessment. Tissues from 90 lobsters from Rhode Island and 19 lobsters from Maine were examined as a general health assessment of the 100 lobsters. Approximately half the lobsters from Rhode Island were selected because they had frank epizootic shell disease, whereas none of the lobsters from Maine exhibited the syndrome. In addition to epizootic shell disease, the histological findings revealed 3 other idiopathic syndromes—necrotizing hepatopancreatitis, idiopathic blindness, and nonspecific granulomas—in higher prevalences in lobsters from Rhode Island compared with those from Maine. Necrotizing hepatopancreatitis, a newly described disease syndrome in lobsters, was observed in 15% of the lobsters from Rhode Island. Idiopathic blindness was present in 54% of the lobsters from Rhode Island, and 16% of the animals from Maine. This is the first report of the syndrome in lobsters from Maine. None of the idiopathic syndromes was associated with epizootic shell disease. The detection of multiple disease syndromes such as epizootic shell disease, necrotizing hepatopancreatitis, and idiopathic blindness may be indicative of exposure to environmental stressors in Narragansett Bay, RI.

Shell disease in Crustacea is a widely recognized syndrome having a polymicrobial etiology, and manifesting itself as lesions of the shell with a variable structure and shell location. We characterized major members of bacterial communities in epizootic shell disease lesions of the American lobster (Homarus americanus, Milne Edwards) and compared these communities with the ones found in study cases of impoundment and enzootic shell disease. Bacteria belonging to several Flavobacteriaceae genera (Aquimarina, Tenacibaculum, Polaribacter, Maribacter, Cellulophaga) within the phylum Bacteroidetes appear to have particular attraction to lobster lesions. The most prominent Bacteroidetes in lobster lesions were representatives of the genus Aquimarina sp., but only Aquimarina ‘homaria’ was detected in all analyzed lesions of epizootic, impoundment, and enzootic shell disease. It was found on 45% of surfaces unaffected by shell disease, but in smaller numbers compared with lesions. Alphaproteobacteria represent the most diverse class of proteobacteria found in both lesions and on unaffected surfaces. Three bacteria of this class appear to be ubiquitous in shell disease lesions, but only one specific alphaproteobacterium tentatively assigned to the genus Thalassobius (herein designated as ‘Thalassobius’ sp.) was present in all analyzed lesions of epizootic, impoundment, and enzootic shell disease. A ubiquitous gammaproteobacterium called ‘Candidatus Homarophilus dermatus’ was also prevalent in lesions, but just as commonly it was associated with surfaces unaffected by shell disease. The bacteria A. ‘homaria’ and ‘Thalassobius’ sp. are dominant and appear obligatory in lobster shell lesions, and are only occasionally detected on unaffected surfaces, which serve as intermediate reservoirs for the two potential pathogens. Therefore, these two bacteria stand out as potential shell-disease pathogens.

Epizootic shell disease (ESD) in the American lobster (Homarus americanus) is continuing to affect the southern New England lobster population, and the etiology of the disease has not been well defined. We hypothesized that a dysbiotic shift in the shell microbial biofilm played a key part in the etiology of the disease. We analyzed the community structure of the surface microflora of apparently healthy and diseased lobsters using multitag pyrosequencing to correlate the abundance of key taxa within the lesions. Discriminant analysis (DA) was used to identify taxa in the microbial community that were associated with diseased and healthy states. Among the 170 bacterial taxa that were identified, 58 were helpful in determining the diseased and healthy states. The remaining 112 were not significantly different between the 2 states. The genus Aquimarina was present in high abundance in both healthy and diseased lobsters, but had a significantly higher abundance on animals in the diseased state. However, DA demonstrated that this genus does not strongly discriminate between the diseased and healthy state. Phylogenetic analysis indicated that there was significant strain diversity of this genus in all the samples analyzed. Our results indicate that the lesions seen in ESD may be viewed as being correlated with a polymicrobial component rather than being caused by a discrete pathogen.

Epizootic shell disease (ESD) is a degradative process of the carapace in the American lobster, (Homarus americanus), putatively caused by bacterial infection, and potentially responsible for serious economic losses to the lobster fishery. In Long Island Sound (LIS), ESD is prevalent in lobsters from eastern LIS (ELIS), but almost absent in western LIS (WLIS), presenting a unique opportunity to examine the influence of microbial communities on the disease process among these subpopulations. Bacterial community compositions in diseased shell, healthy shell subsamples from lobsters exhibiting signs of disease, and carapace subsamples of healthy lobsters from ELIS, WLIS, and a coastal Maine reference site were profiled using terminal restriction fragment length polymorphism (TRFLP). Although overall bacterial community membership in diseased shell was not significantly different from healthy shell and healthy lobsters, prevalence of some individual terminal restriction fragments (TRFs) varied among disease state. Several TRFs were more abundant within lesions, whereas representation of other members appeared to be diminished, particularly members of the β- and γ-proteobacteria. One TRF linked to anaerobic bacteria was enriched in lesions, suggesting anoxic microenvironments within diseased tissues. Activities of 4 ectohydrolases among communities were also measured in replicate excised shell samples. Chitinase potentials were high in all samples, and were indistinguishable among sample types. In contrast, proteinase and cellulase potentials were significantly higher in diseased shell than healthy shell and healthy lobster. Lipase potentials in LIS samples were significantly higher than those from Maine, but similar among disease states. The absence of site-specific differences in microbial communities suggests that biogeographic variation in colonizing microbes is not a factor in disease susceptibility. Lesion development appears to induce compositional shifts in normal carapace microflora, with displacement of some community members as others become more prevalent. Protein and cellulose appear to be more important targets than chitin for bacterial degradation within lesions. Furthermore, lipase activity, degrading the epicuticle lipid layer, may play a key role in regions with high disease prevalence.

Epizootic shell disease (ESD) is an emerging form of shell disease of the American lobster (Homarus americanus) that has had detrimental effects on the fishery in southern New England. Three bacteria commonly isolated from lesions of wild lobsters with ESD—a novel Aquimarina sp. (A. ‘homaria’ I32.4), a novel Rhodobacteraceae species (‘Thalassobius’ sp. I31.1) and a Pseudoalteromonas sp. (Pseudoalteromonas ‘gracilis’ ISA7.3)—were applied directly to normal and abraded juvenile lobster carapaces, and then monitored for persistence over time and for the development of shell-disease lesions at 3 different temperatures (10°C, 15°C, and 20°C). Without abrasion of the carapace, no lesions developed in the exposures. After abrasion and exposure with a pure culture of A. ‘homaria’ I32.4, lesions developed at all 3 temperature and A. ‘homaria’ was detected in the lesions of all animals tested. Surprisingly, ‘Thalassobius’ sp. I31.1 also colonized these lesions. A coexposure with all 3 bacteria also demonstrated lesion development and the persistence of A. ‘homaria’ I32.4 and ‘Thalassobius’ sp. I31.1. The bacterium P. ‘gracilis’ ISA7.3 was not able to persist in any of the challenged lesions. Abraded areas of the cuticle with no bacteria added directly were also colonized by A. ‘homaria’ and ‘Thalassobius’ sp., and moderate lesions developed; however, the directly exposed lesions were significantly more severe (P < 0.05). The bacterium A. ‘homaria’, but not ‘Thalassobius’ sp., was detected in spontaneous lesions that developed independent of any abrasion and/or bacterial exposures. A novel bacterium, ‘Candidatus Kopriimonas aquarianus’ was also detected in spontaneous lesions. This study shows that 2 bacteria isolated from ESD lesions of wild lobsters are able to persist in and act together as important components of lesion development on abraded surfaces of American lobsters. This indicates that they are likely major contributors to lesion development in the ESD polymicrobial infection and may represent significant pathogens of the American lobster.

Epizootic shell disease (ESD) affects lobsters (Homarus americanus) in eastern Long Island Sound (ELIS) and the near-shore waters of southern New England. Marring the shell of individuals, ESD decreases the economic value of infected lobsters and can lead to mortality in severely affected individuals. ESD tends to be most common in areas around Buzzards Bay, RI, and ELIS, and least prevalent in offshore canyons, off Maine's coast, and in western Long Island Sound (WLIS). To investigate the potential role of the immune system in determining an individual's or population's susceptibility to ESD, the immunocompetence and disease status of lobsters with and without signs of ESD from ELIS, WLIS, and Boothbay Harbor, ME, were assessed during late spring (June) 2007. We also measured internal defense parameters of ELIS lobsters during midsummer (August 2007), early fall (October 2007), and the following spring (June 2008) to assess how lobster immune systems respond temporarily. Despite high interindividual variability in defense-related factors, multivariate analyses showed that lobsters from ELIS presented significantly reduced immune responses relative to lobsters from either WLIS or Maine. Disease severity correlated negatively with several immune parameters, suggesting that the higher prevalence of ESD in ELIS may be related, at least in part, to reduced immunocompetency of ELIS lobsters.

Epizootic shell disease (ESD) has been reported widely in American lobster (Homarus americanus, Milne Edwards) in southern New England. The appearance of irregular, deep lesions—characteristic of ESD—has been associated previously with elevated levels of ecdysteroids and premature molting, but the underlying molecular and physiological changes associated with ESD remain poorly understood. Previously, we identified several genes, including arginine kinase and hemocyanin, that were expressed differentially in lobsters exhibiting signs of ESD (diseased) versus those lobsters exhibiting no signs of ESD (assumed healthy), and quantified their expression. In this study, we extend these findings and measure expression of a suite of 12 genes in tissues from 36 female lobsters of varying disease condition. In addition, molt stage is evaluated as a possible confounding factor in the expression of the selected genes. The expression of several genes changed significantly with disease stage. Arginine kinase expression decreased significantly in thoracic muscle of lobsters with signs of ESD. Ecdysteroid receptor expression was elevated significantly in both muscle and hepatopancreas of lobsters with signs of ESD. CYP45, a cytochrome P450 form that was shown previously to covary with ecdysteroid levels and to be inducible by some xenobiotics, showed significantly increased expression in hepatopancreas of lobsters with signs of ESD. Together, these results demonstrate that the expression of several genes is altered in lobsters showing signs of ESD, even when accounting for variation in molt stage. Given the observed changes in ecdysteroid receptor, arginine kinase, and CYP45 expression, further investigations of the association, if any, between molting, muscular function and xenobiotic metabolism and ESD are warranted.

A major role of lobster integument is protection from microbes. Calcite and amorphous calcium carbonate are the most abundant and most acid vulnerable of the cuticle minerals. We propose that calcite is invested in neutralizing an acidifying environment modulated by the epicuticle. A minor cuticle component is carbonate apatite (CAP), proposed to play critical roles in the integument's structural protective function. The CAP of lobster exhibits a flexible composition; its least soluble forms line the cuticular canals most exposed to the environment. A trabecular CAP structure illustrates efficient use of a sparse phosphate resource, cooperating in the hardness of the inner exocuticle. A schematic model of the cuticle emphasizes structural and chemical diversity. A thin outer calcite layer provides a dense microbial barrier that dissolves slowly through the epicuticle, providing an external, alkaline, unstirred layer that would be inhibitory to bacterial movement and metabolism. Injury to the epicuticle covering this mineralized surface unleashes an immediate efflux of carbonate, accentuating the normal alkalinity of an antimicrobial unstirred layer. The trabecular CAP inner exocuticle provides rigidity to prevent bending and cracking of the calcite outer exocuticle. The combined mineral fine structure of lobster cuticle supports antimicrobial function as well as plays a structural protective role.

Epizootic shell disease in the American lobster, Homarus americanus, is seriously affecting inshore populations in southern New England. The disease can change the biochemical profile of lobsters and could potentially change their urine and other body odors. In turn, this may affect social responses, including avoidance of diseased animals. Behavioral avoidance could reduce the spread of disease. We conducted odor choice tests with pairs of (size- and site-matched) healthy and shell-diseased males. The results showed that healthy intermolt females did not prefer the odor of healthy or diseased males significantly. In addition, we investigated the effect of shell disease on male dominance. Healthy males established dominance over shell-diseased males in 15 of 18 fights. Subsequent choice tests with the same male pairs again showed no significant difference between the time females spent with healthy versus diseased males, but they preferred dominant males slightly. Because most dominant males were healthy, it confers a slight advantage to healthy males. The results were similar for animals from 2 subpopulations, each with considerable incidence of shell disease. Behavioral disease avoidance mechanisms were not seen and may have not yet evolved, if this disease is a recent phenomenon. Also, the disease may be caused more by environmental conditions than by genetic predisposition or interanimal contact, making disease recognition irrelevant.

Epizootic shell disease is affecting American lobster (Homarus americanus) populations and the associated fisheries significantly. Historical movement of the disease suggests that temperature has been a critical factor in driving the susceptibility of lobsters to this disease. Here, juvenile lobsters were held in the laboratory at 10°C, 15°C, or 20°C for up to 1,021 days. Survival, growth, and shell disease were tracked throughout, and a separate experiment was conducted to assess the rate at which dietary white lobsters deposited pigment to the cuticle at the different temperatures. In the laboratory, shell disease was tracked as an initial “spot,” the melanization of the cuticle in response to the bacterial ingress, or, as it progressed, a lesion, which was a visible erosion of the shell. The length of the molt cycle (number of days from one molt to the next consecutive molt) was inversely associated with temperature. Average growth (increase in weight and carapace length per molt) at 10°C and 15°C was equivalent and higher than at 20°C, whereas shell disease was greatest at the intermediate temperature. The amount of initial melanization responses to bacteria (spots) was similar across temperatures, but the number of lesions was greatest at 15°C. This is likely a result of the conditions that allow for a combination of longer molt cycles and active bacterial growth, which allowed the disease to progress to the more advanced lesioned state. At the highest temperature, lobsters molted the compromised shell before severe lesion formation could occur. No gross differences in shell structure were observed at the different temperatures. The lack of a linear relationship between shell disease and temperature does not discount temperature as a critical factor in the onset of this disease in lobsters, but signifies that additional factors are important and the disease is complicated and multifactorial in nature. The continued use of a laboratory model system to study this disease further is important to be able to control the multitude of complicating factors appropriately.

Environmental contaminants have been suggested frequently as causative factors in crustacean shell disease. This study explored the relationship of environmental contaminants to epizootic shell disease in the American lobster (Homarus americanus). Trace metal loads were analyzed in lobsters showing signs of shell disease and those without signs of shell disease collected from Narragansett Bay, Rhode Island Sound, and Long Island Sound in 2007. In addition, trace metals were analyzed in lobsters collected in 2008 from a single station in Narragansett Bay and a reference site in Maine for a multiparameter, multiinvestigator study (the “100 Lobsters” project). Analyses focused primarily on hepatopancreas and hemolymph tissues, but muscle, shell, gills, and ovaries were also analyzed to examine the partitioning of metals between various component tissues. Sediment from the “100 Lobsters” collection site was also analyzed. Inductively coupled plasma mass spectrometry (ICP-MS) was used to measure 10 different contaminant elements, including arsenic, cadmium, cobalt, chromium, copper, manganese, molybdenum, nickel, lead, and vanadium. Mercury was determined using a direct mercury analyzer. Overall, there was no systematic difference seen in contaminant metal burdens between those lobsters with signs of shell disease and those without signs, and hepatopancreas concentrations were generally similar to other reported values for field-collected lobsters. Contaminant metals were found to be partitioned between tissues differentially. Hepatopancreas tissue generally contained the greatest concentrations of contaminants, but exoskeleton contained the highest levels of manganese, nickel, and lead. Sediment collected from the “100 Lobster” sampling site showed that concentrations of several metals were similar to or exceeded the suggested sediment quality guidelines, consistent with a site that is moderately impacted by metals. Based on these data, the presence or absence of shell disease cannot be attributed to the magnitude or patterns of metal accumulation and disposition.

Alkylphenols, anthropogenic estrogenic endocrine disruptors in vertebrates, have been found in lobsters (Homarus americanus) in New England sites. We hypothesize that alkylphenols interfere in the shell hardening during molting. We used an in vitro cuticle bioassay to investigate the effects of 2 alkylphenolic compounds—2,4-bis-(dimethylbenzyl) phenol (compound 3) and bisphenol A (BPA; 4,4′-dihydroxy-2,2-diphenylpropane (also referred to as 4,4′-(propan-2-ylidene) diphenol)) on tyrosine incorporation during the hardening of new cuticle following lobster molting. During sclerotization, both alkylphenols and cold tyrosine competed with C¹⁴-tyrosine incorporation in a concentration-dependent manner. This process was also phenoloxidase dependent, as treatment with phenylthiourea (PTU; a phenoloxidase inhibitor) significantly decreased C¹⁴-tyrosine incorporation. We also found that incorporation of C¹⁴-2,4-bis-(dimethylbenzyl) phenol during the shell hardening process was inhibited by cold alkylphenol, cold tyrosine, or PTU, and competition was concentration dependent. Furthermore, incorporation of tyrosine and derivatives into new cuticle decreased with time after molting from 27% incorporation 1 day after a molt to 6% by 4 days after a molt. In nonmolting cuticles, there was no incorporation of alkylphenol or tyrosine derivatives. When lobsters were injected with 2,4-bis-(dimethylbenzyl) phenol during the premolt stage, it took the shells 12 ± 1 days to harden sufficiently to resist deflection by 5 lb pressure exerted by a pressure gauge, compared with 7 ± 1 days for control shells. Thus, shell hardening is delayed significantly by the presence of 2,4-bis-(dimethylbenzyl) phenol. The effects of this compound on shell hardening may result in lobsters' susceptibility to microbial invasion and, therefore, may contribute to the onset of shell disease.

Endocrine-disrupting pollutants in rivers and oceans represent a poorly understood but potentially serious threat to the integrity of aquatic and coastal ecosystems. We surveyed the hemolymph of lobsters from across southern New England and adjacent offshore areas for 3 endocrine-disrupting alkylphenols. We found all 3 compounds in hemolymph from every year and almost every region sampled. Prevalence of contamination varied significantly between regions, ranging from 45% of lobsters from southern Massachusetts to 17% of lobsters from central Long Island Sound. Mean contamination levels varied significantly as a function of region, year sampled, and collection trip, and were highest overall in lobsters from western Long Island Sound and lowest in lobsters from central Long Island Sound. Surprisingly, lobsters from offshore areas were not less contaminated than lobsters from inshore areas. Contamination levels also did not vary as a function of lobster size or shell disease signs. Contaminated lobsters held in the laboratory did not retain alkylphenols, suggesting that hemolymph contamination levels represent recent, rather than long-term, exposure. Our data set is the first, to our knowledge, to survey endocrine-disrupting contaminants in a population across such a broad temporal and spatial scale. We show that alkylphenol contamination is a persistent, widespread, but environmentally heterogeneous problem in lobster populations in southern New England and adjacent offshore areas. Our work raises serious questions about the prevalence and accumulation of these endocrine-disrupting pollutants in an important fishery species.

Management of the American lobster fishery in U.S. waters recognizes 3 biological stocks. Since 2001, the northern 2 stocks have increased in abundance whereas the southernmost stock has declined dramatically. Decline in abundance indices of all sizes, including larvae and young-of-year, indicate that the stock is experiencing recruitment failure. Increasing water temperature and a corresponding increase in shell disease may be contributing factors. Assessment procedures have recently included a 2-fold increase in nonharvest losses; however, modeling spawning stock losses specific to the disease process has not been accomplished. Rebuilding strategies need to maximize stock production while at the same time minimize the spread and severity of shell disease.

The goal of this synthesis is to highlight some of the major findings of the New England Lobster Research Initiative (NELRI), provide a context for these findings based on previous research, discuss the potential impacts of this important emerging disease on the dwindling lobster populations in southern New England (SNE), and provide suggestions on avenues for future research. Most of the research funded in this initiative focused on epizootic shell disease (ESD), the emerging syndrome severely impacting lobster populations primarily in coastal waters in Rhode Island, southern Massachusetts, and eastern Long Island Sound (ELIS), but some new information about other forms of shell disease in lobsters is included. We also discuss how these novel findings on lobster shell disease should be used to inform management of lobster populations.