Research priorities for diseases of the blue crab Callinectes sapidus

The diseases of blue crabs have received relatively little attention compared to those of the American oyster, Crassostrea virginica, or the penaeid shrimps, Penaeus spp. This is primarily due to differences in resource management (fishery vs. aquaculture), and the magnitude of financial losses suffered by the industries from protozoal diseases in oysters and viral diseases in shrimp, respectively. Nonetheless, several agents including Vibrio spp., Hematodinium perezi, Paramoeba perniciosa, Ameson michaelis and Loxothylacus texanus are highly pathogenic in blue crabs, and have the capacity to severely damage certain segments of the crab population. This paper is meant to highlight priorities for critically needed research on the ecological impacts and pathological processes of these diseases in the crab host. It is not meant as a review of the literature. For more complete reviews of the parasites and diseases of blue crabs, see Johnson (1983), Couch (1983), Overstreet (1983), Messick and Sinderman (1992), Noga et al. (1998), Shields and Overstreet (in press)

An investigation into the epizootiology of Hematodinium perezi, a parasitic dinoflagellate in the blue crab, Callinectes sapidus : final report

Hematodinium perezi is a lethal parasitic dinoflagellate that lives in the hemolymph of brachyuran crabs. The parasite is found along the eastern seaboard of the USA where it occurs in epizootics in the commercially important blue crab, Callinectes sapidus. Crab mortalities associated with the disease occur in high salinity waters, typically in poorly draining estuaries. The parasite is prevalent in the seaside bays of the Delmarva Peninsula in the spring and fall, and spreads to the lower reaches of Chesapeake Bay in the fall. In October 1996, the prevalence of the disease along the Virginia portion of the Delmarva Peninsula varied from 20 - 50% in legal crabs. Lower prevalences ( 1-10%) were noted for crabs caught between Cape Henry and Cape Charles, i.e., the mouth of the bay. In November, the prevalence of the disease was notably higher in crabs caught between Cape Henry and Cape Charles (10-30%). The disease can spread into the breeding grounds of adult female crabs, but its prevalence is generally low during the prebreeding and ovigerous season. In Spring and Fall, 1997, the disease had a higher prevalence in the coastal bays and creeks. Infected crabs frequently show signs of weakness and lethargy, and often die due to stress-related handling from fishing. The parasite proliferates to extremely high densities in the host (up to 100 million parasites/ml of hemolymph) over 3 to 6 weeks. The hemolymph undergoes radical changes as evinced by its lack of clotting ability, and marked discoloration. Hemolymph levels of total proteins and acid phosphatase activity change with infection, and indicate a gradual decline in the hosts metabolic resources. The effects of other species of Hematodinium on several crab and lobster fisheries, and data from the present study indicate that H. perezi may have a significant impact on the coastal blue crab fisheries along the Atlantic seaboard of the USA

Climate change enhances disease processes in crustaceans: case studies in lobsters, crabs, and shrimps

Climate change has resulted in increasing temperature and acidification in marine systems. Rising temperature and acidification act as stressors that negatively affect host barriers to infection, thus enhancing disease processes and influencing the emergence of pathogens in ecologically and commercially important species. Given that crustaceans are ectotherms, changes in temperature dominate their physiological and immunological responses to microbial pathogens and parasites. Because of this, the thermal ranges of several crustacean hosts and their pathogens can be used to project the outcomes of infections. Host factors such as molting, maturation, respiration, and immune function are strongly influenced by temperature, which in turn alter the host’s susceptibility to pathogens, further amplifying morbidity and mortality. Microbial pathogens are also strongly influenced by temperature, arguably more so than their crustacean hosts. Microbial pathogens, with higher thermal optima than their hosts, grow rapidly and overcome host immune defenses, which have been weakened by increased temperatures. Pathogen factors such as metabolic rates, growth rates, virulence factors, and developmental rates are often enhanced by rising temperature, which translates into increased transmission, dispersal, and proliferation at the population level, and ultimately emergence of outbreaks in host populations. Less well known are the effects of acidification and salinity intrusion on host-pathogen processes, but they operate alongside temperature, as multiple stressors, that impose significant metabolic and physiological demands on host homeostasis

Mortality and pathophysiology studies of blue crabs infected with the parasitic dinoflagellate Hematodinium perezi

On the eastern seaboard of the USA, populations of the blue crab, Callinectes sapidus, experience recurring epizootics of a parasitic dinoflagellate. The parasite, H ematodinium perezi, fulminates in the summer and autumn causing mortalities in high salinity embayments and estuaries. In laboratory studies, we experimentally investigated host mortality due to the disease, assessed differential hematological changes in infected crabs, and examined proliferation of the parasite. Mature, overwintering, non-ovigerous, female crabs were injected with 103 or 105 cells of H. perezi. Mortalities began 14 dafter infection, with a median time to death of30.3 ± 1.5 d (se). Subsequent mortality rates were greater than 86% in infected crabs. A relative risk model indicated that infected crabs were 7 to 8 times more likely to die than controls, with decreases in total hemocyte densities covarying significantly with mortality. Hemocyte densities declined precipitously (mean= 48 %) within 3 d of infection and exhibited differential changes in subpopulations of granulocytes and hyalinocytes that lasted throughout the course of the infection. Crabs that did not present infections after injection (i.e., immune ) did not show hemocytopenia, and exhibited significant long-term (21-27 d) granulocytemia. Detection of the parasite in the hemolymph of infected crabs increased from approximately 30% after 14 d to 60% after 21 d to 100% after 35 d. Plasmodial stages were, however, detectable in histological preparations of the heart within 3 d of infection and increased in number over 5 and 7 d. Sporulation of the parasite occurred over a short time (at least 4 d, after 43 d infection) and did not culminate in the immediate death of the host. The mortality studies indicate that H. perezi represents a significant threat to the blue crab fisheries in high salinity estuaries, and may have a greater effect on mature females that move to higher salinities to breed

Collection techniques for the analyses of pathogens in crustaceans

Outbreaks of diseases have been reported from a number of ecologically or commercially important crustaceans in tropical, temperature, and boreal waters. The etiology of a disease is often unknown prior to these outbreaks and the effect of the pathogen on the host population is poorly understood. Various techniques can be used to collect, identify, and monitor host populations for pathogens. These include classical methods, such as visual or histological assessment, to more refined techniques, such as simple and quantitative polymerase chain reaction assays. The strengths and weaknesses of the different methods are presented as well as some general guidelines for managing data associated with disease surveys in conjunction with field collections

Hematodinium-Australis N-Sp, a parasitic dinoflagellate of the sand crab Portunus-pelagicus from Moreton Bay, Australia

A new species of parasitic dinoflagellate is described from the portunid crab Portunus pelagicus. The dinoflagellate is a member of the genus Hematodinium which formerly consisted of a single species, H. perezi. Members of the genus have been reported in crabs and lobsters from Europe and North America, where in some circumstances they cause significant mortalities to host populations. The new species is the first member of the family Syndinidae to be fully described from Australia. The new species differs from other forms of Hematodinium primarily by the size of the trophont (vegetative stage), the ovoid plasmodium, and the small beaded form of condensed chromatin in the nucleus. Infection experiments indicated that the parasite may be transmitted within and between the 2 host species. in addition, the pre-patent period of the new form was at least 16 d which is much greater than that reported from other forms

New nemertean worms (Carcinonemertidae) on bythograeid crabs (Decapoda : Brachyura) from pacific hydrothermal vent sites

Several species of crabs from hydrothermal vent sites in the Pacific Ocean Were found to be infested by small, symbiotic nemertean worms. Worms occurred on both male and female crabs, and were located in mucous sheaths adhering to the axillae between the limbs of males and females, the setae of the pleopods of females, and the sterna of infested male and female crabs. Only juvenile and regressed adult worms were observed, primarily because no ovigerous hosts were examined. Similar species of worms mature by eating eggs, then regress or die after host eclosion. Based on the size of the worms from file vent crabs, their habitus with their crustacean hosts, the presence of accessory stylet pouches, and the presence of a single stylet on a large basis (monostiliferous), we place the worms in the family Carcinonemertidae, within the genus Ovicides. Infestations were found on crabs from vent sites on the western Pacific back-arc basins, on the southern East Pacific Ridge, and on the Pacific-Antarctic Ridge, indicating a widespread distribution of the symbioses. This represents the first record of Carcinonemertidae from a deep-sea host, a new host family, Bythograeidae, for these symbionts, as well as the first record of parasitism on a deep-sea bythograeid crab

Atlas of Lobster Anatomy and Histology

This is a histological atlas of the most common organs and tissues found in the American lobster, Homarus americanus. The atlas contains photomicrographs from histological sections of healthy tissues. The atlas contains pictures of tissues that are readily observed in dissection and several that are commonly affected by diseases. It is not a complete atlas. Several organs are not covered, notably the brain, ventral nerve ganglion, sensory organs, and organs associated with molting

Parasitological examination of wasting disease in black abalone, Haliotis cracherodii : final report

Black abalone in southern California are afflicted with chronic intestinal infections of a rickettsia-like organism that causes a debilitating and fatal withering syndrome. The hematology of withered animals indicated that cellular degradation and apoptosis occurred in tandem with the · decline and catabolism of abalone tissues. Two types of hemocytes were found in the hemolymph. Type I and Type II Hyalinocytes were distinguished by subtle differences in their cytoplasmic vesicles. Densities of both types of hemocytes declined in abundance, and small, presumptive stem cells increased in abundance with the progression of the disease. No circulating granulocytes were present in hemolymph; but serous cells were present as fixed granulocytes in hemal spaces. Cellular inclusions, dying cells, and vacuolate cells increased in abundance with the disease. An evaluation of cellular immunity resulted in disparate findings associated with serum levels and types of buffer used. In the presence of micronutrients, and divalent metal ions, however, hemocytes from infected abalone showed increased degrees of phagocytosis (percent phagocytosis, and number of yeast particles per hemocyte) compared to hemocytes from uninfected animals. Experimental transmission of the disease was effected in healthy, unexposed abalone held together with asymptomatic, exposed abalone. Clinical signs of infection appeared after 180 days of cohabitation. The chronic nature of the disease progressed relatively unnoticed until 6 to 8 months when infected abalone began to show signs of withering. The withered condition represented an end stage of the disease and probably resulted from starvation caused by rickettsial disruption of the digestive processes