Shell Disease Research Articles

Characterisation of shell disease syndrome in the brown crab, Cancer pagurus, in a Discrete Irish Sea Fishery

Shell disease is the progressive degradation of a crustacean’s exoskeleton through the secretion of chitinases and other enzymes from a suite of microorganisms. It affects a number of crustacean fisheries worldwide, through increased pre-capture mortality and rendering many individuals unsalable or with a reduced market value. The European edible crab (also known as the brown crab), Cancer pagurus Linnaeus, 1758, is highly susceptible to shell disease, but while intertidal populations have been comprehensively assessed, there has been little attention from a commercial fishery perspective. This study assessed the prevalence (% of catch infected) and severity (% cover of lesions on the carapace) of shell disease in the fishery around the Isle of Man for C. pagurus, in the Irish Sea. Shell disease was assessed in relation to sex and size, and the pattern of infection on ventral and dorsal surfaces described. A total of 2361 individuals was sampled between June and August 2012. Almost 25% of crabs were infected to some degree and of those infected an average of just over 2% of the carapace was covered by lesions. The proportion of individuals infected and the severity of infections was found to increase with size and was greater in males and those exhibiting limb losses. Differences in the pattern of lesions on the carapace between sexes suggest behavioural differences between genders can result in different patterns of individual infection. Both prevalence and severity of the disease varied considerably around the Isle of Man. Based on assessment of eight different fishing grounds, prevalence varied from as low as 15% of the population to as high as 35%, while the severity of infection varied between 0.8% to almost 3%. These findings not only suggest that shell disease syndrome could be causing a significant economic loss in the fishery, but also that environmental factors may be driving the condition. However, further investigation is required to fully elucidate the environmental drivers of this syndrome.

First V-notching experience of a spiny lobster: V-notch recovery and impact on health and growth of Palinurus elephas

V-notching is a conservation technique to delay fishing mortality widely used in fisheries of clawed lobsters. Here we present results of the first V-notching experience of a spiny lobster. The study was conducted on the European spiny lobster Palinurus elephas (Fabricius, 1787) with the aim of assessing: 1) V-notch effects on survival, incidence of shell disease and growth, and 2) the pattern of V-notch regrowth. Results of the 20-month-long tank experiment with 36 lobsters showed that V-notching had no impact on shell disease or growth. However, abnormally high summer temperatures in the experiment lowered survival of V-notched individuals relative to control specimens. Three dimensions of the V-notch mark (depth, width and area) were examined to assess V-notch regrowth, and depth is recommended for regulatory purposes. In this study, four moults, and almost two years, were necessary for V-notch depth to shrink by 50%, an amount that would turn legal a V-notched clawed lobster after one moult. We discuss the applicability of these results under conditions in the wild.

The American Lobster in a Changing Ecosystem: A US–Canada Science Symposium, 27–30 November 2012, Portland, Maine

To the American lobster (Homarus americanus) fishery in the Northeast US and Atlantic Canada, 2012 may have gone down as the year that drove climate change home. An ocean heat wave covered a large swath of the North Atlantic and broke ocean temperature records. It also triggered biological effects that upset the relatively harmonious economics of Canada’s winter and New England’s summer lobster fisheries. The earlymolt induced by the historical warm temperatures put a glut of US lobsters on the market well before the Canadian fishery closed for the season and, in turn, caused a price tumble that even caught the attention of The Wall Street Journal: “Lobster glut slams prices” (WSJ online, 16 July 2012). The story of the American lobster, especially over the last two decades, is one of striking contrasts. Just as lobster abundance in Maine, Nova Scotia, and other parts of Maritime Canada has climbed to historic highs, the fishery in southern New England has collapsed, plagued by disease andmass mortality. In the wake of thewidespread depletion of once diverse ground fish resources, coastal communities in Maine and Atlantic Canada are more economically dependent on the lobster fishery than ever before, and perilously so. Despite its 150-year history, the fishery in this region is seeing record abundance and harvests. Although the boom in lobster production has helped offset ever-rising fuel and bait costs, plummeting prices following the financial crash of 2008 and the ocean heat wave of 2012 precipitated an unforeseen crisis in the business of lobstering. In contrast, in southern New England, hot summers and disease have taken their toll. For the first time, lobster harvesters in Rhode Island have had to consider the prospect of a fishing moratorium. Waters in the southern Gulf of St. Lawrence are also seeingmore frequent bouts of stressful summer temperatures that in some cases have triggeredmass die-offs. Such dramatic changes after decades of relative stability highlight the need for a greater understanding of the American lobster in the context of its changing environment. Acknowledging the merits of the mandate for “ecosystem-based” fishery science and management, fishery managers on both sides of the border are grappling with how to integrate new thinking into traditional single-species approaches. Opportunities for lobster scientists from the US and Canada to gather and talk science are few, but necessary. In the past few years, major research initiatives on the American lobster have been generating ground-breaking results. For example, in the US there has been an infusion of National Oceanic and Atmospheric Administration (NOAA) dollars to examine shell disease in southern New England, and the National Science Foundation’s Coupled Human–Natural Systems Program supports research on the ecology and socio-economics of lobster and groundfish fisheries in the Gulf of Maine. In Canada, the Natural Sciences and Engineering Research Council of Canada (NSERC) supports a lobster research “node” in one of its Strategic Network Capture Fisheries grants, and long-term studies are under way at the University of Prince Edward Island to establish baselines for health parameters and responses to disease and industry-supported fishery enhancement efforts in the Gulf of St. Lawrence. The symposium grew out of a consensus among the scientific community that the response of lobsters to a changing environment is best viewed in an ecosystem context. Whether induced by man or nature, fundamental changes have occurred over the past few decades in the physical environment and food web interactions. The driving questions are as follows:What do we know now that we did not know even a decade ago? What are the common US–Canadian research priorities? How can researchers move forward with an agenda that makes the best use of dwindling funding? The two-and-a-half-day symposium was divided into four themes:

Multiple factors in marine environments affecting lobster survival, development, and growth, with emphasis on alkylphenols: a perspective

A major die-off of the American lobster (Homarus americanus) population in Long Island Sound (LIS) occurred in 1999, involving multiple causes, including increases of temperatures, decreasing oxygen concentrations, and pollutants. Other possible affectors were stress to their immune system, microbial population changes, which may have induced shell disease, water acidification, and insecticides. We examined LIS alkylphenol pollution. Alkylphenols, alkylphenol ethoxylates, and bisphenol A (BPA) are produced in excessive amounts, with BPA estimated at 8 billion pounds per year (1 lb = 0.453 kg). Sixty percent of alkylphenols enter the marine environment and have estrogenic endocrine-disrupting effects on vertebrates. We found multiple effects of alkylphenols on lobsters, on larval survival, molting and postlarval molting, shell hardening, and interference in metamorphosis causing larval–juvenile intermediates. We also found evidence for a basic molecular mechanism of action for alkylphenols through juvenile hormone (JH) and ecdysone receptors. Alkylphenols appear to have contributed to the decrease in the LIS lobster population. We recommend remediation, reducing, or eliminating alkylphenols from the marine environment to protect lobsters as well as other organisms.

Complex etiologies of emerging diseases in lobsters (Homarus americanus) from Long Island Sound

Several diseases have recently emerged in lobsters (Homarus americanus) from Long Island Sound (LIS). Various stressors have been implicated as contributory factors, including increased bottom temperatures, extensive eutrophication with commensurate hypoxia, storm-induced thermal destratification, possible exposures to pesticides and metals, and fishery-induced stressors. Such stressors increase host susceptibility by weakening the host immune defenses and act to increase the transmission and severity of pathogens. The lobster mortality in western LIS in 1999 was linked to Neoparamoeba pemaquidensis, but a complex of stressors resulted in outright mortality from hypoxia or consequent immune suppression that increased susceptibility to the ameba. Similar stressors have been implicated in the etiology of epizootic shell disease and calcinosis. The role of environmental stressors has been hard to delineate, but recent declines in landings indicate that epizootic shell disease has had a negative impact on the lobster population in LIS. Calcinosis, blindness, and hepatopancreatitis are indicators of continued exposure to anthropogenic stressors, but their etiologies remain undetermined. More research is needed to understand emerging diseases, their complex etiologies, and their effects on the lobster population.

Pathology of two forms of shell disease of the American lobster Homarus americanus Milne Edwards in Atlantic Canada

Pathology of two forms of shell disease of the <scp>A</scp>merican lobster <i><scp>H</scp>omarus americanus</i> Milne Edwards in <scp>A</scp>tlantic <scp>C</scp>anada

First case of soft shell disease in Chinese soft-shelled turtle (Trionyx sinens) associated with Aeromonas sobria–A. veronii complex

Outbreaks of an epizootic in Chinese soft-shelled turtle (Trionyx sinensis) in Zhejiang province, China in 2012, caused severe economic losses to turtle culture industry. This disease was characterized by “soft dorsal shell” and “rugose abdominal shell” accompanied by significantly slower growth rate. Six bacterial isolates were collected from livers and kidneys of diseased turtles, and identified as Aeromonas sobria–Aeromonas veronii complex based on morphological and biochemical characteristics and phylogenetic analysis derived from 16S rRNA and six housekeeping genes. These isolates demonstrated pathogenic potential to juvenile Chinese soft-shelled turtles. To our knowledge, this is the first report of large-scale soft shell disease in Chinese soft-shelled turtles.

Bacterial communities associated with lesions of two forms of shell disease in the American lobster (Homarus americanus, Milne Edwards) from Atlantic Canada

Shell disease is a major threat to the American lobster (Homarus americanus, Milne Edwards) fishery. Here we describe the composition of microbial communities associated with lesions of 2 forms of shell disease in Atlantic Canada, (i) a trauma shell disease (TSD) characterized by massive lesions and (ii) an enzootic shell disease (EnSD) characterized by irregularly shaped lesions with a distinct orange to yellow color. The microbiology of the lesions was described by polymerase chain reaction and denaturing gradient gel electrophoresis of 16S rDNA amplified from scrapings of the shell lesions and was compared with communities of unaffected carapaces and previously described forms of shell diseases. Both TSD and EnSD lesions were dominated by members of Alphaproteobacteria, Gammaproteobacteria, and Flavobacteria, all commonly detected in other forms of shell disease; however, unique members of Epsilonproteobacteria were also present. Two Vibrio spp. and 2 Pseudoalteromonas spp. were dominant in lesions of TSD and a Tenacibaculum sp. and Tenacibaculum ovolyticum were dominant in lesions of EnSD. The TSD and EnSD in this study contained similar taxa as other shell disease forms; however, their microbiology is mostly different and neither resembles that of epizootic shell disease.

English

Shells of crabs are infected with a high prevalence&nbsp;of diseases&nbsp;than any other crustacean. Bacteria, viruses, fungi and several other pathogens influence higher percentage of shell disease in crabs. Infections in crab affected&nbsp;growth and metabolism and it may also lead to death. This work deals with the microscopic examination of shell diseased crabs with reference to its variation in hemocytes count, histopathology and biochemical estimation. The total heterotrophic bacterial (THB) population in normal shell was found to be 5.15 x 104&nbsp;&plusmn; 0.09 Colony forming unit (CFU)&nbsp;ml-1&nbsp;and THB load was noted to be slightly increased than in normal shell and the count was 5.95 x 104&nbsp;&plusmn;&nbsp;0.12&nbsp; CFU ml-1&nbsp;in the infected shell. The current findings suggest a positive correlation between bacterial shell disease and the secondary infection affecting hemolymph (total hemocyte count), proximate composition (protein,&nbsp;carbohydrate and lipid) and histopathology of the animal (gills, hepatopancreas and heart). The total hemocyte count and differential count were experimented which showed lower number of total hemocytes in infected crabs while no highly accountable difference was found in differential count. Hematology studies reported total hemocyte as 9.93 x106&nbsp;&plusmn; 0.07 cells ml-1&nbsp;in normal and 6.525 x 106&nbsp;&plusmn; 0.12 cells ml-1in shell diseased hemolymph. The level of protein, carbohydrate and lipid contents suffered a mild alteration in crabs with bacterial shell disease. Histopathology of gills&nbsp;hadshown variations such as dilated lamellae and hemocyte accumulation (nodules), hepatopancreas showed mild difference with increased necrosis, appearance of hemocytic nodules in the hemal spaces and heart with very mere infection while no reportable changes were accomplished in muscle tissue. &nbsp; Key words:&nbsp;Shell disease, bacteria, hematology, histopathology, biochemical composition.

Culture-independent analysis of bacterial communities in hemolymph of American lobsters with epizootic shell disease

Epizootic shell disease (ESD) of the American lobster Homarus americanus H. Milne Edwards, 1837 is a disease of the carapace that presents grossly as large, melanized, irregularly shaped lesions, making the lobsters virtually unmarketable because of their grotesque appearance. We analyzed the bacterial communities present in the hemolymph of lobsters with and without ESD using nested-PCR of the 16S rRNA genes followed by denaturing gradient gel electrophoresis. All lobsters tested (n = 42) had bacterial communities in their hemolymph, and the community profiles were highly similar regardless of the sampling location or disease state. A number of bacteria were detected in a high proportion of samples and from numerous locations, including a Sediminibacterium sp. closely related to a symbiont of Tetraponera ants (38/42) and a Ralstonia sp. (27/42). Other bacteria commonly encountered included various Bacteroidetes, Pelomonas aquatica, and a Novosphingobium sp. One bacterium, a different Sediminibacterium sp., was detected in 20% of diseased animals (n = 29), but not in the lobsters without signs of ESD (n = 13). The bacteria in hemolymph were not the same as those known to be present in lesion communities except for the detection of a Thalassobius sp. in 1 individual. This work demonstrates that hemolymph bacteremia and the particular bacterial species present do not correlate with the incidence of ESD, providing further evidence that microbiologically, ESD is a strictly cuticular disease. Furthermore, the high incidence of the same species of bacteria in hemolymph of lobsters may indicate that they have a positive role in lobster fitness, rather than in disease, and further investigation of the role of bacteria in lobster hemolymph is required.

Tail Rot Disease in Macrobrachium idella idella (Hilgendorf, 1898)

Shell disease may also be referred to as black spot, brown spot or spot disease and was recognized early this century as a problem in impounded population of aquatic animals. The chitinoclastic bacteria which cause shell disease are ubiquitous and infect a wide range of crustaceans, including prawns. All wild and cultured prawns are susceptible to infections; however disease rarely in wild crustaceans due to a lack of overcrowding and less mechanical damage. In the present study the Tail rot disease noticed in the M. idella idella (prawn), which is not common for prawns. The tail rot diseased prawn was tested to bacteriological for enumeration, isolation and biochemical identification of the microorganism.

Laser therapy in a soft-shelled turtle ( Pelodiscus sinensis ) for the treatment of skin and shell ulceration

Skin and shell diseases in aquatic turtles are often associated with several underlying causes. The presented case report describes aetiology including differential diagnoses, diagnostic procedures and therapy of a soft-shelled turtle (Pelodiscus sinensis) suffering from a septicaemic ulcerative dermatitis. Central aspect hereby is the positive curing effect of laser therapy on skin and shell lesions.

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

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.

First Episode of Shell Disease Syndrome in Carcinus aestuarii (Crustacea: Decapoda: Portunidae) in the Volturno River

In this study is reported the first episode of a Shell Disease Syndrome (SDS) in wild specimens of Carcinus aestuarii from the polluted Volturno River estuary. Collected crabs showed erosive and ulcerative “black spot” lesions on the exoskeleton; histologically the lesions ranged from a mild to extensive and severe damages and intense haemocyte infiltration. Bacterial isolation confirmed the presence of some marine bacterial species with chitinolytic activity. The authors suggest that the detection of sds in wild crabs living in polluted waters could be used to monitor the health status of this environment.

Increased Disease Calls for a Cost-Benefits Review of Marine Reserves

Marine reserves (or No-Take Zones) are implemented to protect species and habitats, with the aim of restoring a balanced ecosystem. Although the benefits of marine reserves are commonly monitored, there is a lack of insight into the potential detriments of such highly protected waters. High population densities attained within reserves may induce negative impacts such as unfavourable trophic cascades and disease outbreaks. Hence, we investigated the health of lobster populations in the UK’s Marine Conservation Zone (MCZ) at Lundy Island. Comparisons were made between the fished, Refuge Zone (RZ) and the un-fished, No-Take Zone (NTZ; marine reserve). We show ostensibly positive effects such as increased lobster abundance and size within the NTZ; however, we also demonstrate apparent negative effects such as increased injury and shell disease. Our findings suggest that robust cost-benefit analyses of marine reserves could improve marine reserve efficacy and subsequent management strategies.

Shell Disease in Callinectes rathbunae Contreras, 1930, Parasitized by Loxothylacus texanus Boschma, 1933

Shell Disease in Callinectes rathbunae Contreras, 1930, Parasitized by Loxothylacus texanus Boschma, 1933

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

The emergence of epizootic shell disease in American lobsters Homarus americanus in the southern New England area, USA, has presented many new challenges to understanding the interface between disease and fisheries management. This paper examines past knowledge of shell disease, supplements this with the new knowledge generated through a special New England Lobster Shell Disease Initiative completed in 2011, and suggests how epidemiological tools can be used to elucidate the interactions between fisheries management and disease.

Bacterial Communities Associated with Lesions of Shell Disease in the American Lobster,Homarus americanusMilne-Edwards

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.

A Fisherman's Perspective

A Fisherman's Perspective

Relationship between Temperature and Shell Disease in Laboratory Populations of Juvenile American Lobsters (Homarus americanus)

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.