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Hematodinium is a type of parasitic dinoflagellate that infects marine crustaceans globally. The parasite lives mainly in the hemolymph or hemocoels of affected hosts, and results in mortalities due to malfunction or loss of functions of major organs. In recent years, the parasite had developed into an emerging epidemic pathogen not only affecting wild populations of economically valuable marine crustaceans in western countries but also the sustainable yield of aquaculture of major crabs in China. The epidemics of the parasitic diseases expanded recently in the coastal waters of China, and caused frequent outbreaks in aquaculture of major crab species, especially Portunus trituberculatus and Scylla paramamosain. In addition, the pathogen infected two species of co-cultured shrimps and multiple cohabitating wild crabs, implying it is a significant threat to the sustainable culture of commercially valuable marine crustaceans. In particular, the polyculture system that is widely used along the coast of China may facilitate the spread and transmission of the pathogen. Thus, to provide a better understanding of the biological and ecological characteristics of the parasitic dinoflagellate and highlight important directions for future research, we have reviewed the current knowledge on the taxonomy, life cycle, pathogenesis, transmission and epidemiology of Hematodinium spp. Moreover, ecological countermeasures have been proposed for the prevention and control of the emerging infectious disease.

Parasitic dinoflagellates in genus Hematodinium have caused substantial economic losses to multiple commercially valuable marine crustaceans around the world. In the present study, comprehensive omics approaches (miRNA transcriptomics, iTRAQ-based proteomics) were applied to investigate the host-parasite interaction between hemocytes from Portunus trituberculatus and Hematodinium perezi. The parasitic dinoflagellate remodeled the miRNome and proteome of hemocytes from challenged hosts, modulated the host immune response at both post-transcriptional and translational levels and caused post-transcriptional regulation to the host immune response. Multiple important cellular and humoral immune-related pathways (ex. Apoptosis, Endocytosis, ECM-receptor interaction, proPO activation pathway, Toll- like signaling pathway, Jak-STAT signaling pathway) were significantly affected by Hematodinium parasites. Through modulation of the host miRNome, the host immune responses of nodulation, proPO activation and antimicrobial peptides were significantly suppressed. Cellular homeostasis was imbalanced via post-transcriptional dysregulation of the phagosome, peroxisome, and lysosome pathways. Cellular structure and communication was seriously impacted by post-transcriptional downregulation of ECM-receptor interaction and focal adhesion pathways.Author summaryThe parasitic dinoflagellate Hematodinium infects many economically important marine crustaceans. Recent efforts to better understand the life cycle and biology of the parasite have improved our understanding of the disease ecology. However, studies on the host-parasite interaction, especially how Hematodinium parasites evade the host immune response are lacking. To address this shortfall, we used miRNA transcriptomics and iTRAQ-based proteomic approaches to explore the immune responses of Portunus trituberculatus when challenged with Hematodinium perezi. Striking changes in the miRNome and proteome of hemocytes were observed, and the parasite exhibited multifaceted immunomodulatory effects and potential immune-evasion mechanisms in this crustacean host.

Background The parasitic dinoflagellates of the genus Hematodinium represent the causative agent of so-called bitter or pink crab disease in a broad range of shellfish taxa. Outbreaks of Hematodinium-associated disease can devastate local fishing and aquaculture efforts. The goal of our study was to examine the potential role of the common shore (green) crab Carcinus maenas as a reservoir for Hematodinium. Carcinus maenas is native to all shores of the UK and Ireland and the North East Atlantic but has been introduced to, and subsequently invaded waters of, the USA, South Africa and Australia. This species is notable for its capacity to harbour a range of micro- and macro-parasites, and therefore may act as a vector for disease transfer. Methods Over a 12-month period, we interrogated 1191 crabs across two distinct locations (intertidal pier, semi-closed dock) in Swansea Bay (Wales, UK) for the presence and severity of Hematodinium in the haemolymph, gills, hepatopancreas and surrounding waters (eDNA) using PCR-based methods, haemolymph preparations and histopathology. Results Overall, 13.6% were Hematodinium-positive via PCR and confirmed via tissue examination. Only a small difference was observed between locations with 14.4% and 12.8% infected crabs in the Dock and Pier, respectively. Binomial logistic regression models revealed seasonality (P P Hematodinium detection with peak infection recorded in spring (March to May). Male crabs overall were more likely to be infected. Phylogenetic analyses of the partial ITS and 18S rRNA gene regions of Hematodinium amplified from crabs determined the causative agent to be the host generalist Hematodinium sp., which blights several valuable crustaceans in the UK alone, including edible crabs (Cancer pagurus) and langoustines (Nephrops norvegicus). Conclusions Shore crabs were infected with the host generalist parasite Hematodinium sp. in each location tested, thereby enabling the parasite to persist in an environment shared with commercially important shellfish.

The parasitic dinoflagellate Hematodinium is considered an important pathogen of economically important marine crustaceans and has been reported from many wild and cultured species. While limited studies have been conducted to reveal the host-parasite interaction in crustaceans, the underlying molecular mechanisms between Hematodinium and its crustacean hosts are scarcely known. We conducted a comprehensive study to investigate the proteomic responses to Hematodinium infection in the hepatopancreas of Portunus trituberculatus using an iTRAQ-based quantitative proteomic technology. A total of 905 identified proteins including 392 differentially expressed proteins (DEPs) were subjected to GO, COG and KEGG-pathway enrichment analysis, with sixteen DEPs further validated by quantitative real-time PCR. Hematodinium parasites resulted in immune-suppressive and adverse effects on affected hosts, thorough inhibition of the important pattern recognition receptors (C-lectin, SR class B, and Toll)-mediated immune responses, regulation of the complement and coagulation pathway, dysregulation of important cell adhesion molecules and extracellular matrix, and imbalance of the cellular redox homeostasis in the hepatopancreas of affected crabs. Moreover, the lysosomes pathway was dysregulated seriously in the hepatopancreas of P. trituberculatus post Hematodinium challenge. The results provided evidences on how the Hematodinium parasite overcame the innate immunity of P. trituberculatus and caused pathological alteration in affected tissues Biological significance The manuscript presented the first iTRAQ-based proteomic study of the host-parasite interaction between an important marine crustacean and the parasitic dinoflagellate Hematodinium. The manuscript reported the key pathways and proteins involved in the host-parasite interactions. The major findings will contribute to the better understanding of the molecular mechanism of the particular host-parasite interaction, as wells as the pathogenic process in susceptible tissues of affected crustacean hosts.

Host, pathogen, and environment are determinants of the disease triangle, the latter being a key driver of disease outcomes and persistence within a community. The dinoflagellate genusHematodiniumis detrimental to crustaceans globally – considered to suppress the innate defences of hosts, making them more susceptible to co-infections. Evidence supporting immune-suppression is largely anecdotal and sourced from diffuse accounts of compromised decapods. We used a population of shore crabs (Carcinus maenas), whereHematodiniumsp. is endemic, to determine the extent of collateral infections across two distinct environments (open water, semi- closed dock). Using a multi-resource approach (PCR, histology, haematology, population genetics, eDNA), we identified 162Hematodinium-positive crabs and size/sex-matched these to 162Hematodinium-free crabs out of 1,191 analysed. Crabs were interrogated for additional disease-causing agents; haplosporidians, microsporidians, mikrocytids,Vibriospp., fungi,Sacculina, trematodes, and haemolymph bacterial loads. We found no significant differences in occurrence, severity or composition of collateral infections betweenHematodinium-positive andHematodinium-free crabs at either site, but crucially, we recorded site-restricted blends of pathogens. We found no gross signs of host cell immune reactivity towardHematodiniumin the presence or absence of other pathogens. We contendHematodiniumsp. is an immune-evader rather than immune-suppressor, which suggests an evolutionary drive toward latency in this environmentally plastic host.

Tanner crab ( Chionoecetes bairdi ) are an economically important species that is threatened by ocean warming and Bitter Crab Disease, which is caused by an endoparasitic dinoflagellate, Hematodinium . Little is known about disease transmission or its link to host mortality, or how ocean warming will affect pathogenicity or host susceptibility. To betterunderstand how temperature and infection influence host physiology, we performed a temporal transcriptomic analysis on crab infected with Hematodinium and uninfected crab exposed to either ambient (7.5˚C), elevated (10˚C), or decreased (4˚C) temperature treatments. After assembling a transcriptome and performing a multifactor differential gene expression analysis, we found genes influenced by temperature in relation to infection, and detected some of those genes over time at the individual level using RNAseq data from one crab. Biological processes associated with those genes include lipid storage, transcription, response to oxidative stress, cell adhesion, and morphogenesis. Alteration in lipid storage and transcription provide insight into how temperature impacts energy allocation in Hematodinium infected crabs. Alteration in expression patterns in genes associated with morphogenesis could suggest hemocytes were changing morphology and/or type in response to temperature. This project provides insight into how Hematodinium infection could influence crab physiology as oceans warm.

Marine ecosystems are affected by multiple, well-known stressors like fishing and climate change, but a less documented concern is disease. Marine reserves have been successful in replenishing stocks and aiding recruitment but studies have shown that high population abundances in marine reserves may lead to unwanted secondary effects such as increase in predators and competition, altering trophic webs, and disease. Here, we investigate factors contributing to disease prevalence in a brown crab (Cancer pagurus) population around Lundy Island (the UK's first MPA) after 7 years of no-take protection. Population parameters (size, sex, and abundance), disease (shell disease, Hematodinium spp. infection) and injury presence (a known precursor to some disease conditions) were assessed over two years in both fished and unfished areas of the MPA. We found no significant difference in prevalence between the disease prevalence in fished and unfished areas, however overall, the number of injured crabs increased significantly over the two years (12%), as did the prevalence of shell disease (15%). The probability of crabs having shell disease increased significantly in male crabs, and in those missing limbs. The probability of crabs being injured increased significantly in crabs below the minimum landing size. In terms of population parameters, crabs were more prevalent in the fished area compared to the unfished area, thought to be a result of an increase in the predatory European lobster. The findings of the present study highlight potential secondary community changes as a result of MPA implementation. Therefore, surveillance for such changes, as part of MPA management, would provide useful information on the health and overall function of the protected ecosystem.

The parasitic dinoflagellates of the Hematodinium genus have impacted wild and cultured stocks of commercial crustaceans worldwide. In the past decade, outbreaks of Hematodinium epizootics resulted in substantial mortalities in cultured Chinese swimming crabs Portunus trituberculatus in the polyculture ponds located in Shandong Peninsula, whereas the source and transmission of the parasite in the polyculture pond system remains to be determined. During April to December of 2018, 2034 crabs and 108 shrimps were collected from the polyculture pond systems in the highly endemic area of Hematodinium diseases in Qingdao, Shandong Province. Among those, 188 individuals of the 6 crab species were infected by the parasite, including 4 novel host species (Uca arcuate, Hemigrapsus penicillatus, Helice wuana and Macrophthalmus japonicas). No infection was identified in Penaeus monodon. Further phylogenetic analyses indicated that the Hematodinium isolate infecting the six crab hosts, together with other isolates reported from China, composed the genotype II of Hematodinium perezi. The parasite was more infectious to cultured Portunus trituberculatus and the dominant wild crab Helice tientsinensis dwelling in the waterways connecting to the polyculture ponds, even though it was found to be a host generalist pathogen. The prevalence of Hematodinium perezi infection in Helice tientsinensis was higher than that of other wild crabs and showed significant positive correlation with that of the cultured Portunus trituberculatus. The results indicated that the wild crabs, particularly Helice tientsinensis, were the important alternate hosts closely involved in transmission and spreading of the Hematodinium disease in the polyculture pond systems.

A disease caused by parasitic dinoflagellates of the genus Hematodinium has been found in the soft crab Hapalogaster grebnitzkii from the Sea of Okhotsk, which is considered a new host for this agent among lithodid crabs. This report provides macro- and micromorphological descriptions (using light and transmission electron microscopy) of the disease, as well as molecular identification of Hematodinium sp. from soft crabs, based on 18S RNA sequence data.

A parasitic dinoflagellate of the genus Hematodinium was found off the Pacific coast of Kamchatka in three species of crabs: red king crab Paralithodes camtschaticus, tanner crab Chionoecetes bairdi, and spiny king crab Paralithodes brevipes. This is the first detection of Hematodinium in spiny king crab. The results of the genetic analysis showed that the pathogen found in P. brevipes, P. camtschaticus, and C bairdi from the Avacha and Kronotsky bays off the Pacific coast of Kamchatka was the same or very close to the Hematodinium sp., which infects many species of crustaceans in the Northern Hemisphere. The prevalence of infection was 0.2% for tanner crabs and 2.7% for red king crabs. Due to a limited sample size, we were unable to calculate the prevalence for spiny king crabs and female red king crabs. Both the macroscopic and microscopic signs of the pathology were similar in all diseased crabs. The differences in the micromorphology of the Hematodinium cells we found in the three crab species, including the presence or absence of trichocysts, the shape of the plasmodia, and the structure of pore complexes, are most likely related to the life cycle and the physiology of the parasite. The results of the genetic analysis showed that the pathogen found in P. brevipes, P. camtschaticus, and C. bairdi from the Avacha and Kronotsky bays of the Pacific coast of Kamchatka was the same or very close to the Hematodinium sp., which infects many species of crustaceans in the Northern Hemisphere.

The parasitic dinoflagellate Hematodinium spp. infects a broad range of marine crustaceans. Its epidemics have impacted wild populations of various commercial fishery species around the world and the sustainability of mariculture in China. To study the epidemiology of Hematodinium spp. in marine crustaceans along the coast of China, we conducted a broad survey of wild and cultured stocks of major crustacean species in 2013 to 2015. Hematodinium sp. infections were identified in wild stocks of Portunus trituberculatus from Huludao, Laizhou, Qingdao, Yangtze River Estuary and Zhoushan, and Scylla paramamosain from Shantou; and cultured stocks of Portunus trituberculatus and Penaeus monodon from a polyculture pond in Qingdao. In the polyculture pond, Hematodinium sp. infections were observed in Portunus trituberculatus from June until October, with peak prevalence (up to 90%) observed in late July to early August. Furthermore, Hematodinium sp. infection was identified for the first time in the giant tiger prawn Penaeus monodon in the polyculture system during the disease outbreak. Phylogenetic analysis indicated that the Hematodinium isolate infecting Penaeus monodon was identical to the isolate infecting the co-cultured Portunus trituberculatus, and it was grouped into H. perezi genotype II together with the other isolates reported in China. The Hematodinium sp. isolated from Portunus trituberculatus appeared to have similar life stages as the H. perezi genotype III isolated from the American blue crab Callinectes sapidus. Our study indicates that outbreaks of Hematodinium disease can be a significant threat to the widely used polyculture system for decapods in China that may be particularly vulnerable to such generalist pathogens.

The landing obligation of the reformed European Union Common Fisheries Policy is designed to encourage more selective fishing strategies and improve recording of catches. There are allowable exemptions to this landing obligation including for species with high post-release survivability. Discarding patterns of prawns (Nephrops norvegicus) were evaluated in a trawl fishery in the Firth of Clyde, West Scotland which supplies the live-catch market. Around 30% of the Nephrops caught were discarded but the reasons for discarding changed seasonally. Using visual indices, physiological biomarkers and video recordings this study evaluated the physiological condition linked to short-term survival and predator avoidance behaviour of the discarded animals. Although short-term survival after 48 h recovery was high (around 90%) and physiological measures indicated that discarded Nephrops can recover from trawling, survival was negatively affected by levels of physical damage and Hematodinium infection. Taking into consideration these factors a conservative estimate for discard survival was 63-88%. Underwater video showed that Nephrops discarded in good condition rapidly recovered normal behaviour when placed on the seabed. Moribund animals, however, took up to 10 minutes to return to an upright posture and this time was sufficient for predators to be attracted. Since around 20% of Nephrops were in a moribund condition immediately after trawling, the survival estimates based upon enclosed recovery experiments may need correcting by up to this amount to account for potential interactions with predators on the seabed. The post-release survival rates in discarded Nephrops suggested for this fishery are relatively high compared with other Nephrops trawl-fisheries which have been studied. This could be explained because this fishery targets the live-market, prioritises product quality over volume and uses short-duration tows leading to relatively low levels of physical damage to the Nephrops.

The parasitic dinoflagellate Hematodinium infects multiple cultured marine crustaceans and has resulted in significant economic losses to their aquaculture in China. Limited molecular data implied a close relationship among Hematodinium reported in China, whereas the genetic diversity and detailed genetic variation within Hematodinium remains unclear. In order to investigate the genetic diversity and composition of the parasitic dinoflagellate in China, the sequences of the internal transcribed spacer region (ITS1 - 5.8S - ITS2) were amplified from 104 infected hosts cultured in three geographic locations. Two strains were identified, Hematodinium perezi II was the prevalent strain observed in all three host taxa throughout the survey, the other novel one was detected from the single Exopalaemon carinicauda collected from Zhejiang province. Eight ITS haplotypes within H. perezi II were identified with a similarity of 99.8% -100%. The distinct haplotype compositions and AMOVA analysis suggested a significant genetic differentiation and population structure among the three geographic populations of H. perezi II. The novel strain, genetically affiliated with H. perezi, was quite divergent from the three known genotypes (I, II and III) of H. perezi, and further investigation is needed to determine the distribution and host range of this new strain.

We studied the distribution of the “bitter-crab” syndrome, a disease caused by the parasitic dinoflagellate Hematodinium sp., in eight commercial species of crabs in the west of the Bering and Chukchi seas. The crabs (25 388 individuals) were sampled during bottom trawl surveys of July‒September 2010 and October‒November 2012. The disease was first identified visually by a color change of the exoskeleton and the hemolymph of the animals and then using microscope analysis of hemolymph samples. Infestation was detected in crabs of three species, Chionoecetes opilio, C. bairdi, and Paralithodes platypus. The prevalence of the disease (the percent of infected individuals relative to all of those examined) in C. bairdi and P. platypus was very low, 0.1 and 0.3%, respectively. Infestation was widespread among C. opilio, its peak in the Bering Sea was in the fall. The average prevalence of the crab disease in different areas of the Bering Sea ranged from 0.8 to 10.8%. A high rate of crab infection was recorded in the Korfa Bay. In the Chukchi Sea, the average prevalence was 2%. Infestation by Hematodinium sp. was not revealed in the deep-sea snow crabs Chionoecetes tanneri and C. angulatus, and in three species of lithodid crabs, Paralithodes camtschaticus, P. brevipes, and Lithodes couesi. This can be explained by the small sample volume and/or ecology of these species, since the disease was registered in other areas in four of them.

Latest studies have indicated that microRNAs (miRNAs) play important roles in defending against bacterial and viral infections in marine crustacean, whereas little is known regarding the immunological roles of crustacean miRNAs in response to parasitic infection. To further reveal the host-parasite interactions between the parasitic dinoflagellate Hematodinium and its crustacean hosts, we applied the high-throughput sequencing technology to identify and characterize miRNAs in the Chinese swimming crab Portunus trituberculatus challenged with the Hematodinium parasite at a timescale of 16 days (d). A total of 168 miRNAs were identified and 51 miRNAs were differentially expressed in the hepatopancreas tissues of affected hosts. Eleven of the differentially expressed miRNAs were selected and verified by the quantitative real-time RT-PCR (qRT-PCR), manifesting the consistency between the high throughout sequencing and qRT-PCR assays. Further analysis of the putative target genes indicated that various immune-related pathways (e.g. endocytosis, Fc gamma R-mediated phagocytosis, lysosome, ECM-receptor interaction, complement and coagulation cascades, antigen processing and presentation, focal adhesion, etc.) and signal transduction pathways (e.g. JAK-STAT signaling pathway, MAPK signaling pathway, p53 signaling pathway, etc.) were mediated by the differentially expressed miRNAs. The results presented fundamental knowledge on the immunological roles of crustacean miRNAs and contributed to the better understanding of hosts' miRNAs-mediated immunity against the parasitic infection.

The blue crab Callinectes sapidus is an invasive alien species in the Mediterranean Sea. In native habitats, it suffers mortalities determined by different pathogens, including viruses, dinoflagellates, and bacteria. In invaded habitats, scant information is available on the occurrence of parasites in blue crabs, and no comparisons have been made with native brachyuran species. Here, a preliminary screening of the hemolymph of C. sapidus hemolymph as well as of three indigenous crabs (Eriphia verrucosa, Carcinus aestuarii and Pachygrapsus marmoratus), captured in the Acquatina Lagoon (Salento Peninsula, SE Italy), evidenced the presence of unidentified protozoans in more than 70% of the analyzed specimens, with a low number of suspected infections due to dinoflagellates of the genus Hematodinium. In C. sapidus, the occurrence of parasites was accompanied by a decrease of hemocyte functionality, interfering with the role of the cells in innate immunity (i.e. phagocytosis or DOPA production). More studies are necessary in order to verify the impact of this alien brachyuran on invaded ecosystems as mediated by the spread of its parasites and other pathogens.

To assess the ability of adult blue crab (Callinectes sapidus) to function under the hypoxic conditions becoming increasingly common in their inshore habitats, critical oxygen levels (i.e., the minimum oxygen levels at which aerobic metabolism can be maintained) were determined over a range of metabolic rates using automated intermittent-flow respirometry. Different metabolic rates were induced by conducting experiments at three temperatures (17°, 23°, and 28 °C), testing recently fed crabs, and those infected with the parasitic dinoflagellate Hematodinium perezi. The effects of hypoxia on the metabolic rates and recovery times of individuals following enforced exhaustive activity, and metabolic rates following feeding, were also measured to determine the levels of hypoxia likely to impact feeding, digestion, and overall energetics. Contrary to previously published results, blue crab were found not to be partial oxygen conformers (i.e., where metabolic rate falls in concert with reductions in ambient oxygen), but rather to be oxygen regulators (i.e., to have the ability to maintain a constant aerobic metabolic rate until the critical oxygen level was reached). By this measure, at routine metabolic rates blue crab are as hypoxia-tolerant as other decapod crustaceans with a median critical oxygen level of ~ 20% air saturation (at 17° and 23 °C). Critical oxygen levels increased in concert with the increases in metabolic rate occurring at 28 °C, in individuals infected with H. perezii, and those recently fed. At the highest metabolic rates (measured in recently fed individuals at 28 °C) median critical oxygen level was ~ 45% air saturation. Consistent with this latter observation, metabolic rates after feeding or exercise were not compromised until below 50% air saturation, although maximum metabolic rates were lower at this level of hypoxia. The results presented are consistent with the oxygen levels shown to influence blue crab behaviors (~ 2 to 4 mg l− 1) in both field and laboratory settings.

Parasitic dinoflagellates in the genus Hematodinium cause disease and mortality in several commercially important marine decapod crustaceans. One species, Hematodinium perezi, occurs in blue crabs, Callinectes sapidus, along the eastern seaboard and Gulf coast of the USA. The parasite infects blue crabs, other decapods, and amphipods in the high salinity waters of coastal bays. Epizootics of the parasite often reach prevalence levels of 75-80% during outbreaks with diseased crabs dying from the infection. Prevalence of the parasite is bimodal, with a minor peak in late spring or summer, and a major peak in fall, and declining rapidly to nearly zero in late November and December. The rapid decline in infections in the late fall brings up the question of whether the parasite overwinters in crabs or whether it uses an unidentified resting stage, such as a cyst. We report observations on the prevalence of the parasite from winter dredge surveys undertaken in 2011 and 2012. Crabs were examined via hemolymph smears, histology, and PCR diagnosis for the presence of H. perezi and other pathogens. Active infections were observed from January through March in 2011 and 2012, indicating the parasite can overwinter in blue crabs. However, several crabs that were positive by PCR had presumptive effete infections that were difficult to diagnose in histological slides and hemolymph smears. These infections did not appear to be active and may have been in subsidence. Dredged crabs with light and moderate active infections were held at 15°C to determine if the parasite was capable of rapid progression. In 8 cases, infections exhibited logarithmic growth progressing rapidly over 8-12days. We present evidence that overwintering of H. perezi occurs in the blue crab hosts, that infections are capable of responding rapidly to increases in temperatures, and that overwintering provides a reservoir of infected animals for transmission to occur in the spring.

Tail flip escape swimming was measured in the Norway lobster, Nephrops norvegicus (Linnaeus, 1758) up to cessation and following 4 hours recovery, and was compared with that of lobsters infected by the parasitic dinoflagellate Hematodinium sp. Swimming in uninfected lobsters comprised around 65 high-power flips in Phase 1 and a variable number of less powerful flips in Phase 2. Lightly-infected lobsters executed fewer flips in Phase 2, and heavily-infected lobsters produced only a few weak flips. Following 4 hours recovery uninfected lobsters produced 84.3% of the flips produced initially, due to a smaller number of Phase 2 tail flips. Infected lobsters showed less recovery, proportional to the severity of infection. The metabolic basis of the two-phase swimming pattern and the reduced performance during infection by Hematodinium is discussed. Our findings have implication for the catchability of uninfected and infected N. norvegicus, especially on fishing grounds where the fishing effort is high.

The dinoflagellate Hematodinium perezi is a highly pathogenic endoparasite that infects blue crabs Callinectes sapidus and other decapods. Annual outbreaks of the parasite along the eastern seaboard of the USA indicate that transmission occurs at high rates; however, the timing and incidence of new infections are unknown. The aim of this study was to investigate the patterns and factors associated with the natural transmission of Hematodinium in juvenile crabs from a highly endemic site. A novel field experiment, using naive crabs as sentinels, was implemented to measure transmission. Over 965 juvenile crabs (instars C3–C10) collected from a non-endemic site were deployed for set periods of 3, 7, 10, and 14 days at a highly endemic site. Prevalence was 5.1% after a 3-day deployment and 88% after a 10-day deployment. This corresponded to a daily incidence of new infections of 1.7 and 8.8%, in the population, respectively. New infections progressed very quickly; 50% of infected crabs developed heavy infections after only 14 days. The influence of host molting on the transmission of the parasite was investigated by tagging 467 crabs using cyanoacrylate glue and small plastic tags. After 7-, 10-, and 14-day deployments, sentinel crabs were assessed and infections were found not to be associated with host molting. Lastly, two storm events, with high rainfall, strong winds, and lower temperatures, disrupted the natural transmission of H. perezi to sentinel crabs, essentially halting transmission in the coastal system. These sentinel studies indicate that transmission can occur rapidly and at very high levels in endemic sites and that it can be quickly modulated by changes in environmental conditions following storm events. Infections by Hematodinium may increase host mortality and thus may be a threat to blue crab populations in endemic areas.

Infectious diseases threaten marine populations, and the extent of their impacts is often assessed by prevalence of infection (the proportion of infected individuals). Changes in prevalence are often attributed to altered rates of transmission, although the rates of birth, recovery, and mortality also determine prevalence. The parasitic dinoflagellate Hematodinium perezi causes a severe, often fatal disease in blue crabs. It has been speculated that decreases in prevalence associated with high temperatures result from lower rates of infection. We used field collections, environmental sensor data, and high-temperature exposure experiments to investigate the factors that change prevalence of infections in blue crab megalopae (post-larvae). These megalopae migrate from offshore waters, where temperatures are moderate, to marshes where temperatures may be extremely high. Within a few days of arriving in the marsh, the megalopae metamorphose into juvenile crabs. We found a strong negative association between prevalence of Hematodinium infection in megalopae and the cumulative time water temperatures in the marsh exceeded 34°C over the preceding two days. Temperatures this high are known to be lethal for blue crabs, suggesting that higher mortality of infected megalopae could be the cause of reduced prevalence. Experimental exposure of megalopae from the marsh to a temperature of 34°C resulted in higher mortality for infected than uninfected individuals, and decreased the prevalence of infection among survivors from 18% to 3%.

5 - Abstract: Mitochondria and plastids were acquired by endosymbiotic event, where prokaryotic organism was engulfed by ancestors of extant eukaryotes. There are more known endosymbiotic events in plastid evolution. In primary endosymbiosis cyanobacterium cell was engulfed by heterotrophic eukaryotic organism. In following secondary, tertiary and quaternary endosymbiotic events eukaryotic cell was engulfed by another eukaryote. Mitochondria originated by engulfment of α-proteobacteria. In the evolution of eukaryotes, reduction of mitochondria occurred in many lineages, making living under anaerobic conditions possible. The least reduced form is anaerobic mitochondria, which together with aerobic mitochondria and hydrogen producing mitochondria, possess genome. Hydrogenosomes and the most reduced form mitosomes, does not possess genome. Plastid reductions led to loss of photosynthetic ability. In last years, more examples of organisms that lost entirely their semi- autonomous organelle, are coming. Loss occur at two parasitic representatives of the Alveolata group, and one endobiotic oxymonad. Parasites Cryptosporidium parvum and Hematodinium lost nonphotosyntetic plastid, whereas Monocercomoides lost its mitochondria. Semi-autonomous organelles were dispensable, because all representatives have access to...

Blue crabs (Callinectes sapidus) living in high salinity regions along the Atlantic and Gulf coasts of the United States are subject to infection by the parasitic dinoflagellate Hematodinium perezi with a prevalence that can exceed 50%. Infections are usually lethal, thus H. perezi infection represents a significant cause of mortality in many crab populations. Most studies of this host-parasite interaction have focused on epidemiology, host-pathogen dynamics, and pathogen transmission; little is known about the impact of the parasite on host behavior and population dynamics. We examined the effects of H. perezi on blue crab mortality from predation, activity patterns, and habitat use. Infected crabs suffered significantly higher predation than uninfected crabs when tethered in the field. Similarly, infected juvenile crabs were preyed upon significantly more often than uninfected conspecifics when exposed to a predatory adult crab in laboratory experiments. Laboratory experiments also revealed that the behavior of infected and uninfected crabs differed in ways that affected their risk of predation. Compared to infected crabs, uninfected juvenile crabs buried more frequently, moved less, and used oyster shell substrate more often when a predator was present. These differences do not appear to be driven by olfactory cues because chemosensory assays show that H. perezi infections do not affect detection of juvenile crabs by adult crabs, nor infected juvenile crab chemosensory responses to adult crabs. Our results indicate that H. perezi infection alters crab behavior in ways that enhance predatory culling of infected crabs, and this in turn may limit the spread of the parasite.

Hematodinium is a parasitic dinoflagellate of numerous crustacean species, including the economically important Atlantic snow crab, Chionoecetes opilio. The parasite was cultured in vitro in modified Nephrops medium at 0 °C and a partial characterization of the life stages was accomplished using light and transmission electron microscopy (TEM). In haemolymph from heavily infected snow crabs two life stages were detected; amoeboid trophonts and sporonts. During in vitro cultivation, several Hematodinium sp. life stages were observed: trophonts, clump colonies, sporonts, arachnoid sporonts, sporoblasts and dinospores. Cultures initiated with sporonts progressed to motile dinospores; however, those initiated with amoeboid trophonts proliferated, but did not progress or formed schizont-like stages which were senescent artefacts. Plasmodial stages were associated with both trophonts and sporonts and could be differentiated by the presence of trichocysts on TEM. Macrodinospores were observed but not microdinospores; likely due to the low number of Hematodinium sp. cultures that progressed to the dinospore stage. No early life stages including motile filamentous trophonts or gorgonlocks were observed as previously noted in Hematodinium spp. from other crustacean hosts. All Hematodinium sp. life stages contained autofluorescent, membrane-bound electron dense granules that appeared to degranulate or be expelled from the cell during in vitro cultivation.

Trichocyst morphology and development were explored using transmission electron microscopy in Hematodinium spp. isolated directly from Atlantic snow crab ( Chionoecetes opilio ) hemolymph and from in vitro cultures. Appearance of trichocysts defines the initiation of a morphological transition in the parasites life cycle from vegetative stage to the transmission stage. Trichocysts within sporonts were found in distinct clusters near the nucleus in close apposition to the Golgi. As cells transitioned to more mature dinospores however, trichocysts were found randomly distributed throughout the cytoplasm. Clusters contained both primordial and maturing trichocysts at various stages indicating an asynchronous development. The random distribution of mature trichocysts suggests deployment to the cell membrane for future extrusion. Mature trichocysts of Hematodinium spp. appeared structurally similar to trichocysts from photosynthetic dinoflagellates. Hematodinium spp. trichocysts differed by the presence of peripheral tubules associated with novel cuboidal appendages in the apical region rather than a network of central electron dense fibres as found in photosynthetic dinoflagellates. Additionally, the trichocyst membrane of Hematodinium spp. was in close apposition to the square crystalline core. Trichocyst expulsion was not observed during our study which along with features of development and maturation within Hematodinium life stages should provide insight into proposed roles in host attachment or defense that could further our understanding of the mechanisms of pathogenesis and transmission of the parasite.

Since 2012, frequent outbreaks of Hematodinium diseases have significantly impacted sustainable culture of marine crabs Portunus trituberculatus in the coastal areas of Shandong Peninsula. The mechanisms of the Hematodinium parasite epizootics in polyculture pond systems remain to be explored and alternate crustacean hosts are speculated to play important roles in transmission and epizootiology of the disease. To investigate their possible role in transmission, the common wild mudflat crabs Helice tientsinensis were sampled from the waterway connecting to polyculture ponds in Huangdao, Qingdao, China and diagnosed for Hematodinium infection. Hematodinium infection was found in H. tientsinensis collected in the waterway from April–November 2018, with a prevalence of 5.8–31.7%. In addition, 23.1% of H. tientsinensis sampled from the adjacent polyculture pond were infected during the peak of the Hematodinium epizootic in July. Amoeboid trophonts or prespores were observed in the hemolymph of the Hematodinium-infected crabs and histopathological changes were observed in major organs (e.g. hepatopancreas, heart, gill and muscle). The ITS1 rRNA of Hematodinium sp. infecting H. tientsinensis shared 99–100% similarity to isolates infecting P. trituberculatus and Penaeus monodon in local polyculture ponds, and are included in a monophylogenetic clade, Hematodinium perezi genotype II, in the phylogenetic tree. The results further showed that this generalist parasite was infecting various types of marine crustaceans in the coastal waters of China, and that mudflat crabs H. tientsinensis may serve as an important alternate host during epizootics of Hematodinium parasites in the polyculture system.

Hematodiniumperezi (genotype III) is a parasitic dinoflagellate that infects blue crabs along the eastern seaboard and Gulf of Mexico, USA. In order to examine the intra-specific genetic variation of this parasite, eleven microsatellite markers from H. perezi (III) were amplified from 227 infected blue crabs collected during 2008–2009 from six sites in Virginia. Simultaneous infections with multiple genetic types in a single-host individual were common and observed in 42 % of the samples. The remaining 58 % of samples had a single allele per locus at all eight polymorphic loci suggesting that the life history stages of the parasite in the host hemolymph are likely haploid. The composition and distribution of multi-locus genotypes (MLG) from samples with infections of a single genetic type indicated high genotypic variation along the Delmarva Peninsula, Virginia, with no evidence of population structure. The lack of linkage disequilibrium combined with the large number of unique MLGs (84 %) is strong evidence for recombination in the life cycle, but the sexual stages remain undetermined. This is the first evidence of ploidy level, infections by multiple genetic types in an individual host animal, high levels of genotypic variation, and sexual reproduction for any species of Hematodinium.

Juvenile edible crabs, Cancer pagurus L., were surveyed from Mumbles Head and Oxwich Bay in South Wales, UK, and the number of heterotrophic bacteria and vibrios in the hemolymph was determined. The percentage of crabs with hemolymph containing bacteria was variable over the survey with higher numbers of animals affected in summer than in winter. Post-moult crabs contained significantly higher numbers of heterotrophic bacteria in the hemolymph than pre- and intermoult animals. Crabs with cuticular damage to the gills also had significantly higher numbers of bacteria in the hemolymph. Crabs were found to have a high prevalence of infection by the dinoflagellate, Hematodinium. Such animals had significantly fewer bacteria in the blood in comparison with Hematodinium-free animals. Of the 463 crabs surveyed, only 3 individuals had hemolymph containing 2000 + CFU mL(-1). Based on 16S rRNA gene sequences, two of these crabs contained a Vibrio pectenicida-like isolate, while the other had a mixed assemblage of vibrios. Although 59% of the crabs surveyed had culturable bacteria in the hemolymph, the majority only had small numbers (2000 CFU mL(-1) ), suggesting that such infections may be of limited importance to the sustainability of the crab fishery in this region.

Since 2004, the parasitic dinoflagellates Hematodinium emerged as causative agent of the "milky blood disease" in cultured Portunus trituberculatus, Scylla serrata and Exopalaemon carinicauda along the coastal areas of southern China; while, no Hematodinium infections had been reported in northern China. We sampled P. trituberculatus in polyculture ponds and adjacent coastal waters from two sites in Shandong Peninsula, the major culture region in northern China which contributes to one third of the national gross outcome of the crab species. Hematodinium infections were identified in 10% of P. trituberculatus randomly sampled from polyculture ponds, while no infections were observed in wild crabs collected from adjacent coastal waters. Filamentous trophonts and amoeboid trophonts were observed in diseased crabs. The Hematodinium sp. shares similar morphologic features and causes typical pathological changes in hepatopancreas, heart, and muscles of infected hosts as other Hematodinium spp. The laboratory trials indicated that this parasite was infectious and caused pathological alterations to crab hosts as those diseased crabs from culture ponds. Molecular analysis indicated that the isolates were closely related to those reported in southern China. Our findings indicate an alarming broad distribution of the infectious pathogen along the coastal areas of China. The polyculture pond system widely used in major culture regions in China may prompt transmission or spread of Hematodinium among susceptible hosts, which urges pressing investigation of its major routes of transmission in such culture system along with better understanding of its life cycle. (c) 2013 Elsevier B.V. All rights reserved.

This study reports on an emerging fungal disease of the edible crab, Cancer pagurus . Juvenile (prerecruit) crabs were found to be subject to this disease condition during the months of May to September at two intertidal sites in South Wales, United Kingdom. Histopathology revealed that the fungi overwhelm the host response in the tissues, leading to progressive septicemia. The causative agent of this infection was isolated and grown in pure culture and was identified as a member of the Ophiocordyceps clade by sequencing of the small subunit of the fungal ribosomal DNA (rDNA). Of the crabs naturally infected with the fungus, 94% had a coinfection with the parasitic dinoflagellate Hematodinium species. To determine if there was any interaction between the two disease-causing agents, apparently fungus-free crabs, both with and without natural Hematodinium infections, were challenged with the fungal isolate. The presence of Hematodinium caused a significant reduction in fungal multiplication in the hemocoel of the crabs in comparison to that in Hematodinium -free individuals. Histopathology of coinfected crabs showed a systemic multiplication of Hematodinium within host tissues, leading to a rapid death, while Hematodinium -free crabs experimentally infected with the fungal isolate died due to fungal sepsis (septicemia) with the same characteristic pathology as seen in natural infections.

The dinoflagellate Hematodinium perezi is a prolific pathogen of the blue crab Callinectes sapidus along the Atlantic and Gulf of Mexico coasts of North America. High prevalence, sometimes approaching 100%, and outbreaks with high mortality are associated with higher salinities. H. perezi has not been reported previously in blue crabs from Louisiana, USA, where salinities in coastal habitats are generally below the parasite's favorable range. However, the possibility that H. perezi infects blue crabs in higher salinity habitats offshore has not been investigated. A PCR-based test for H. perezi was used to screen blue crabs collected from both high and low salinity areas. These included juvenile and adult crabs from inshore marshes where salinities are relatively low and from higher salinity offshore shoals that are spawning sites for females. H. perezi was detected in blue crabs from offshore shoals (prevalence=5.6%) but not in juvenile or adult crabs from inshore habitats. Megalopae (post-larvae) were also collected from inshore locations. Although megalopae settle inshore where salinities are relatively low, the megalopal stage is preceded by a planktonic phase in higher salinity offshore waters. We detected H. perezi in 11.2% of settling megalopae tested. Although the prevalence of H. perezi was relatively low within our samples, if spawning females and megalopae are especially vulnerable, the impact on the population could be compounded. This is the first report of H. perezi from blue crabs in Louisiana and demonstrates the importance of examining all life stages in determining the prevalence of a harmful parasite.

Blue crab, Callinectes sapidus, commercial landings in the USA have been declining at an alarming rate. In South Carolina, these declines are significantly correlated with years of decreased rainfall and elevated salt marsh salinity. Previous studies suggest that higher salinity increases the risk of infection by Hematodinium sp., a dinoflagellate parasite of blue crabs, C. sapidus. A 4-year survey (June 2008 to March 2012) of blue crabs in the ACE Basin National Estuarine Research Reserve documented (1) the temporal and spatial patterns of Hematodinium sp. infection in relation to salinity, (2) some environmental correlates of disease prevalence, and (3) the characteristics of infected blue crabs. Sampling was conducted four times a year in March, June, September, and December in the South Edisto, Ashepoo, and Combahee rivers beginning in June 2008. Crab hemolymph samples were collected and preserved and DNA was successfully amplified for 2,303 individuals. Hematodinium sp. infection was evaluated by PCR amplification of its 18S rRNA gene and adjacent regions. Prevalence was highest in December 2008 in the Combahee River at sites closest to St. Helena Sound. The spatial and temporal pattern of Hematodinium sp. infection was correlated with several environmental parameters. Infected crabs exhibited differences in carapace shape and body condition compared to uninfected crabs. Overall, these results suggest that blue crabs in regions of higher salinity are at greater risk of infection by Hematodinium sp. and infected individuals exhibit sub-lethal effects of the disease.

Hematodinium and Hematodinium-like species have emerged in the last 3 decades as important parasitic pathogens of crustaceans worldwide, causing a significant economic loss to fisheries and related markets. In some species (notably the Tanner crab Chionoecetes bairdi), the parasite reportedly causes the cooked meat to taste bitter and aspirin-like. The bitter taste, together with the gross pathology of the infection, renders these crabs unmarketable. Surprisingly, no organoleptic tests have ever been conducted to date, and the cause for the bitter taste is still unknown. Nevertheless, it is generally assumed that the bitter taste occurs widely in cooked meats and products derived from crustaceans infected with Hematodinium. In the present study, we analysed the meat quality and organoleptic attributes after capture and during storage of Norway lobsters Nephrops norvegicus from Scottish waters that were either asymptomatic or symptomatic of patent Hematodinium infection. Results from the sensory evaluation of the cooked product indicate that tail meat from symptomatic N. norvegicus is bland in flavour and aftertaste, and more friable or sloppier in texture than meat from asymptomatic animals. As a consequence, infected meat tends to be less palatable, although surprisingly no bitter taste is reported. From an analytical point of view, tail meat from patently infected animals is at an advanced stage of autolysis, while no difference in microbial load is detected. These results suggest that Norway lobsters heavily infected with Hematodinium are of inferior marketing quality even after the tails have been cooked.

Lobsters are prized by commercial and recreational fishermen worldwide, and their populations are therefore buffeted by fishery practices. But lobsters also remain integral members of their benthic communities where predator-prey relationships, competitive interactions, and host-pathogen dynamics push and pull at their population dynamics. Although lobsters have few reported pathogens and parasites relative to other decapod crustaceans, the rise of diseases with consequences for lobster fisheries and aquaculture has spotlighted the importance of disease for lobster biology, population dynamics and ecology. Researchers, managers, and fishers thus increasingly recognize the need to understand lobster pathogens and parasites so they can be managed proactively and their impacts minimized where possible. At the 2011 International Conference and Workshop on Lobster Biology and Management a special session on lobster diseases was convened and this special issue of Diseases of Aquatic Organisms highlights those proceedings with a suite of articles focused on diseases discussed during that session.

Recent studies of the fisheries for the Norway lobster, Nephrops norvegicus (L.), have illustrated the negative effects of pathogens and of the physiological stresses of capture processes on the exploitation of live animals and their products, and have identified mitigating measures. Firstly, having established that trawl capture of N. norvegicus is highly stressful, but that these animals have powerful physiological mechanisms of recovery, procedures for on-board recovery of animals destined for vivier transport to distant European markets have been implemented commercially, with significant improvements in survival rates. Such procedures also mitigate against the initiation of a stress-induced muscle necrosis. Secondly, measurements of post-mortem autolytic and spoilage processes have identified the existence of a post-capture 'handling window' of several hours which allows the whole or tailed products to be preserved, by icing or freezing, without detriment to quality. Commercial consortia of Scottish fishermen are exploiting this opportunity to extend product shelf-life by freezing at sea within this handling window. Thirdly, the well-documented infections of Scottish N. norvegicus populations by the dinoflagellate Hematodinium sp. not only provide examples of pathogen-induced mortality, but also have effects on post-harvest products including vivier transport losses and changes in post-mortem degradation leading to earlier organoleptic rejection. Under commercial conditions these effects can be mitigated by post-capture visual screening, but only during the periods of peak patent infection when parasitised animals are visually identifiable. Wider implementation of such mitigating procedures during the harvesting of wild-caught crustaceans will contribute to a more sustainable exploitation of these valuable marine resources.

Hematodinium species are parasitic dinoflagellates known to infect a growing number of marine crustacean genera from around the world, many of which support important commercial fisheries. Affected hosts undergo dramatic pathological alterations to their organs, tissues and hemolymph. There are no known control measures for this disease. Economically important wild fished hosts known to be susceptible to Hematodinium spp. include Tanner crabs Chionoecetes bairdi and snow crabs Chionoecetes opilio in the Northeast Pacific and Atlantic Oceans, blue crabs Callinectes sapidus from the Atlantic and Gulf coasts of the United States, and Norway lobsters Nephrops norvegicus and Edible crabs Cancer pagurus from European waters. In recent years, several farmed aquatic crustaceans in China have also been negatively impacted by Hematodinium-associated diseases, likely representing an emerging issue for that expanding industry. Molecular sequence data indicates that there are two species, Hematodinium perezi, and a second species, currently unnamed, infecting hosts from the Northern Hemisphere. Three subtly different H. perezi genotypes have been identified infecting hosts from different geographical locations: the English Channel, the eastern seaboard of the United States and Gulf of Mexico, and eastern China. Genotypic variability between isolates of the Hematodinium sp. infecting hosts from the North Atlantic and North Pacific has also been reported, though it is unclear whether there is any correlation with host or location. Identification of Hematodinium species (and genotypes of H. perezi) is largely dependent upon geographical location, rather than host species. However this is not exclusive, as both Hematodinium species can be found infecting multiple species from same location, as is the case in the English Channel.

Hematodinium sp. infections are relatively common in some American blue crab (Callinectes sapidus) populations in estuaries of the western Atlantic Ocean. Outbreaks of disease caused by Hematodinium sp. can be extensive and can cause substantial mortalities in blue crab populations in high salinities. We examined several species of crustaceans to determine if the same species of Hematodinium that infects C. sapidus is found in other crustaceans from the same localities. Over a 2-yr period, 1,829 crustaceans were collected from the Delmarva Peninsula, Virginia, examined for the presence of infections. A portion of the first internal transcribed spacer (ITS1) region of the ribosomal RNA (rRNA) gene complex from Hematodinium sp. was amplified and sequences were compared among 35 individual crustaceans putatively infected with the parasite, as determined by microscopic examination, and 4 crustaceans putatively infected based only on PCR analysis. Of the 18 crustacean species examined, 5 were infected with Hematodinium sp. after microscopic examination and PCR analysis, including 3 new host records, and an additional species was positive only via PCR analysis. The ITS1 rRNA sequences of Hematodinium sp. from the infected crustaceans were highly similar to each other and to that reported from C. sapidus (98%). The similarity among these ITS1 sequences and similarities in the histopathology of infected hosts is evidence that the same species of Hematodinium found in C. sapidus infects a broad range of crustaceans along the Delmarva Peninsula. Our data indicate that the species of Hematodinium found in blue crabs from estuaries along the east coast of North America is a host generalist, capable of infecting hosts in different families within the Order Decapoda. Additionally, evidence indicates that it may be capable of infecting crustaceans within the Order Amphipoda.

Crustaceans worldwide are infected with alveolate parasites of the genus Hematodinium, causing substantial losses to langoustine and crab fisheries. The distinct seasonality in Hematodinium occurrence in their decapod hosts, as well as unsuccessful attempts at transmission, suggest the existence of life stages outside their benthic crustacean hosts. We used a nested polymerase chain reaction method to detect Hematodinium rDNA in the environment and in potential alternative hosts. Environmental samples from the Clyde Sea, Scotland, were screened during the April release of dinospores and during June and August, when infection prevalence is rare in benthic crustaceans. Hematodinium rDNA was amplified in 15% (14/94) of isolated langoustine larvae, and in 12% (13/111) of crab larvae. In addition, Hematodinium rDNA was present in mixed plankton samples devoid of decapod larvae, but including the 2 μm–10 mm fraction of particulate organic matter in the water column, containing phytoplankton and other zooplankton. These results indicate that Hematodinium occurs in the water column and is harboured by planktonic organisms, including larval stages of the crustacean hosts, when infections are at their lowest in adult hosts.

Mullowney, D. R., Dawe, E. G., Morado, J. F., and Cawthorn, R. J. 2011. Sources of variability in prevalence and distribution of bitter crab disease in snow crab (Chionoecetes opilio) along the northeast coast of Newfoundland. – ICES Journal of Marine Science, 68: . Bitter crab disease (BCD), caused by a parasitic dinoflagellate of the genus Hematodinium, is a source of mortality in Newfoundland and Labrador snow crab (Chionoecetes opilio). Prevalence and distribution patterns have been spatially and temporally variable since the discovery of BCD in 1990, and controlling factors are poorly understood. Data from a long-term trap survey in two bays along the northeast coast of Newfoundland are analysed, investigating the influences and interactions of various biotic and abiotic factors over BCD. Factors examined include host size and density, temperature, salinity, and depth. The density of small to medium-sized snow crabs was directly related to prevalence and distribution of BCD, whereas all other factors had either an indirect or no effect. Further, much of the spatio-temporal variability in disease expression is a function of variability in host productivity, growth, and movement. The study also considers the impacts BCD can exert on the commercial fishery, and the potential for predicting intermediate to long-term recruitment potential based on BCD prevalence levels.

Protists are a diverse group of eukaryotes that possess a unicellular level of organization. As unicellular organisms, the differentiation of cells into tissues does not occur, although when cell differentiation does occur, it is limited to sexual reproduction, alternate vegetative morphologies or quiescent life history stages. Protistan parasites may possess simple or complex life histories that are important factors to consider when investigating protistan diseases of decapods. Unfortunately, the life histories of many protistan parasites of decapods are insufficiently described, resulting in the fact that modes of infection and transmission are often unidentified. This is surprising considering the economic importance of many marine decapods and the ability of protistan parasites to produce significant, but generally transient and area limited mortalities. However, the marine disease landscape is changing and will continue to change as climate change and ocean acidification will play important roles in disease occurrence and distribution. As a result, the following discussion attempts to summarize current knowledge on several crab diseases, their protistan etiological agents, the impact of disease on economically important crab populations and draw attention to areas of needed research. The discussion is not complete as only selected diseases are addressed, or perfect as the Microsporidia are included in the discussion (a traditional error continued in this summary) despite the recent, but controversial placement of the taxon with the fungi.

A disease caused by a parasitic dinoflagellate of the genus Hematodinium was identified in red, Paralithodes camtschaticus, and blue, Paralithodes platypus, king crabs from the north-east region of the Sea of Okhotsk, Russia, during annual stock surveys. No carapace color change was observed even in heavily infected crabs, but diseased crabs possessed creamy-yellow hemolymph, which was visible through the arthrodial membranes of the abdomen and appendages. Several stages of the parasite's life history, including trophonts, plasmodia, sporonts and macrodinospores, were observed in tissues of infected king crabs. Numerous parasite cells were observed in the lumina of the myocardium, the gills, the connective tissue of antennal glands and the sinuses of nerve ganglia, eyestalks and gastrointestinal tract of king crabs with gross signs of infection. Based on sequencing of the 18S rDNA, it appears that the Hematodinium sp. found in red and blue king crabs is identical or closely related to Hematodinium sp. isolated from crabs of the genera Chionoecetes and Lithodes. Observed prevalences were 0.33% in sublegal male red king crabs, 0.18% in female red king crabs, 0.34% in sublegal male blue king crabs and 0.31% in female blue king crabs.

Five decapod crustacean species were examined for presence of the parasitic dinoflagellate Hematodinium spp. (Alveolata, Syndinea) by morphological methods (colour and pleopod methods) as well as by PCR and nested PCR with Hematodinium-specific primers. Nephrops norvegicus, Pagurus bernhardus and Liocarcinus depurator were sampled by trawling in Danish waters and Chionoecetes opilio and Hyas araneus were sampled by trapping off the west coast of Greenland. The existence of Hematodinium has not previoiusly been documented in Danish waters, but it was detected in all 3 decapod species examined in the present study. Hematodinium sp. was also detected for the first time in H. araneus and the existence of Hematodinium sp. in Greenlandic C. opilio was documented by PCR. Analyses of 26 Hematodinium sp. ITS1 sequences, including sequences from all 5 host species sampled, revealed more than 95% sequence similarity between 24 of the sequences. Two Hematodinium sp. ITS1 sequences from C. opilio were only 81% similar to the 24 other ITS1 sequences. The nested PCR approach resulted in the highest reported percentages of positive samples for Hematodinium sp.in the hosts investigated (between 45 and 87.5%). However, no decapods were found to be infected with Hematodinium sp. based on morphological methods. Consequently, Hematodinium sp. may be more common than previously believed, and, assuming that the DNA found originated from viable and infectious parasite cells, infections may not always be fatal. We suggest that the hosts investigated may have been subject to latent infections that could develop into a fatal disease only if the hosts were physiologically stressed due to other factors.

Species of Hematodinium are highly pathogenic parasitic dinoflagellates and can cause substantial mortalities in many decapod crustaceans. Periodic outbreaks of Hematodinium disease have significantly impacted stocks of the blue crab Callinectes sapidus throughout the Delmarva Peninsula. Using a primer set targeting the internal transcribed spacer region 1 (ITS1) of the ribosomal RNA (rRNA) gene complex of Hematodinium , we confirmed the presence of the parasite's DNA in water and suspended sediment samples collected from Virginia estuaries of the Delmarva Peninsula by polymerase chain reaction (PCR) on DNA extracted from these environmental samples. Amplicon sequences were highly conserved and 99–100% similar to the ITS1 sequence of the endemic Hematodinium sp. reported from blue crabs in the region. A sensitive real-time PCR assay was developed and validated for the detection and quantification of the parasite DNA. The assay has a limit of detection of less than one parasite cell in 100 ml of environmental water or one gram of sediment; it will provide a valuable tool for our ongoing studies on the transmission dynamics of this parasite. The real-time PCR assay was further tested on a free-living stage of Hematodinium . Sporulation resulting in the release of millions of Hematodinium dinospores from heavily diseased crabs was observed in the laboratory. Some dinospores survived up to 7 days in aquaria outside of the crab host. We speculate that the Hematodinium sp. dinospores have a short free-living stage in the water column and that transmission to new hosts must occur relatively quickly in estuarine habitats.

Hematodinium is a genus of parasitic dinoflagellates that infects crustaceans worldwide including Tanner crabs Chionoecetes bairdi and snow crabs C. opilio in the Northeast Pacific Ocean. The present study describes the optimization of a PCR-based assay for the detection and monitoring of Hematodinium sp. in snow and Tanner crabs. Two fragments, 1682 and 187 bp, were amplified from the 18S ribosomal DNA region of the parasite. The assay performed well in 6 additional deca- pod species (1 lobster and 5 crabs) infected with Hematodinium spp., suggesting that it could be used to detect Hematodinium spp. in other decapods. We also report Hematodinium spp. infections in the majid crab, Hyas coarctatus, and the lithodid crab, Lithodes couesi. Sequencing of 18S rDNA and the adjacent internal transcribed spacer 1 (ITS1) region of Hematodinium spp. isolated from 7 host spe- cies in the present study revealed the presence of 2 Hematodinium clades, one in the blue crab Call- inectes sapidus and a second in all other host species. The ITS1 sequences of the 2 clades could not be aligned, but showed a conserved secondary structure that may be related to a functional diversi- fication during a host switch. Comparison of our data with 18S and ITS1 sequence data available in GenBank placed the north Pacific Hematodinium sp. in a clade separate from the Hematodinium sp. infecting the portunoids, C. sapidus, Liocarcinus depurator and Scylla serrata, and within a second clade that infected all other decapod hosts located in the North Pacific and North Atlantic Oceans.

The effects of four different ante-mortem stressors (exercise, emersion, starvation and a patent infection with the parasite Hematodinium sp.) on post-mortem processes have been investigated in the abdominal muscle of Norway lobster Nephrops norvegicus by measuring changes in the pH, the levels of glycogen, l-lactate, arginine phosphate, ATP, ADP, AMP, IMP, HxR, Hx and the adenylate energy charge (AEC) over a time course of 24 h with samples being taken at 0, 3, 6, 12 and 24 h. The acute stresses of intense exercise and 2 h emersion resulted in a premature onset of anaerobic glycolysis, leading both to an enhanced glycogen depletion rate and an early accumulation of l-lactate. The chronic stressors, starvation and parasite infection, resulted in a complete ante-mortem depletion of muscle glycogen and consequently the failure of post-mortem glycolytic fermentation. Post-mortem pH and ATP inter-conversion were significantly altered in chronically stressed animals. Ante-mortem, a rapid, almost compl...

Parasitic dinoflagellates in the genus Hematodinium are highly pathogenic to crustaceans. This study presents the first report of Hematodinium infection in shrimps in China. Various forms of the parasite were observed in affected ridgetail white prawn Exopalaemon carinicauda — uninucleate, binucleate and multinucleate sporonts, and occasionally motile dinospores. The parasite caused profound pathological changes in gills, hepatopancreas, heart, and muscles of infected hosts. This parasite was the primary causative agent of the milky shrimp disease which occurred in cultured ridgetail white prawn in eastern China in 2008, and resulted in up to 100% mortality in affected polyculture ponds in Zhoushan, Zhejiang province, China. The pathogen apparently can be transmitted among susceptible hosts in the polyculture ponds. The parasite shared similar antigenic determinants with the Hematodinium sp. identified in the Chinese swimming crab Portunus trituberculatus. Results of histopathology, ultrastructure examination, immunological and molecular identification indicated that this parasite is the same species as that identified in the Chinese swimming crab, P. trituberculatus and mud crab, Scylla serrata from China. Our preliminarily phylogenetic analysis indicated that the parasite is closely related to the Hematodinium sp. identified in C. sapidus and has distinct genetic distance from the Hematodinium sp. identified in northern Europe.

In the absence of distinct morphological characteristics, knowledge of genetic relationships within and between protist parasite species is important for determining reservoir hosts and understanding the biology of the causative agents of emerging diseases. The genus Hematodinium is a member of Syndinea, an ubiquitous alveolate group found in all oceanic environments. Hematodinium parasites cause epizootics in crustaceans, yet their life cycle, genotypic variety and their phylogeny is poorly understood. By combining phylogenetic methods with analyses of secondary structures of variable ribosomal RNA genes we show that Hematodinium from the east and west North-Atlantic is comprised of distinct ribotypes or clades. These did not correspond to a specific area, but varied in host specificity. For example, a Hematodinium 'Langoustine' clade was only found in Nephrops norvegicus langoustines, whereas other clades were specific to crabs or seem to be generalist parasites.

Infection with the parasitic dinoflagellate Hematodinium sp. can be devastating to blue crab Callinectes sapidus populations. Morbidity and mortality appear to depend on the burden of parasitic organisms. Heavily infected crabs become lethargic and, if not preyed upon, succumb to overwhelming infection. We report on the transmission of Hematodinium sp. into blue crabs that were fed pieces of infected tissues and examined for evidence of infection at time periods from 1 to 48 h and for the general state of their health after 4 d. During the first 16 h after feeding, Hematodinium sp. was found in the gut, followed by large increases in hemolymph hemocytes and the appearance of hemocytic nodules in tissues. By 16 h, the hemocytic nodules appeared poorly circumscribed and disorganized. No nodules were seen in a heavily infected crab after 24 h. By the end of the 48 h after feeding, 73% (11 of 15) of the crabs had shown evidence of infection with Hematodinium sp. Those crabs with infection intensities (Hematodinium sp. as percent of cells in hemolymph) higher than 20% were dead within 4 d.

Hamilton, K. M., Shaw, P. W., and Morritt, D. 2009. Prevalence and seasonality of Hematodinium (Alveolata: Syndinea) in a Scottish crustacean community. – ICES Journal of Marine Science, 66: 1837–1845. Protist parasites of the genus Hematodinium were detected in seven crustacean species (Cancer pagurus, Carcinus maenas, Liocarcinus depurator, Munida rugosa, Necora puber, Pagurus bernhardus, and Pagurus prideaux) from the Clyde Sea in Scotland. Seasonal screening of different tissues with sensitive molecular probes showed average infection of 3–23%, with prevalence reaching almost 60% in hermit crabs (P. bernhardus) and brachyuran hosts in spring and >30% in C. pagurus and N. puber in autumn. During summer, Hematodinium infections were rare. Hematodinium seemed to be present in all host sizes sampled. The infection was equally distributed between males and females in most host species, except C. maenas, where males seemed to be more susceptible to infection. PCR amplification of the Hematodinium ribosomal RNA gene in crustacean tissue detected the parasite most frequently in muscle, gills, and heart throughout the 2-year sampling period.

Hematodinium sp. is a parasitic dinoflagellate infecting the blue crab Callinectes sapidus and other crustaceans. PCR-based assays are currently being used to identify infections in crabs that would have been undetectable by traditional microscopic examination. We therefore sought to define the limits of quantitative PCR (qPCR) detection within the context of field collection protocols. We present a qPCR assay based on the Hematodinium sp. 18S rRNA gene that can detect 10 copies of the gene per reaction. Analysis of a cell dilution series vs. defined numbers of a cloned Hematodinium sp. 18S rRNA gene suggests a copy number of 10 000 per parasite and predicts a sen- sitivity of 0.001 cell equivalents. In practice, the assays are based on analysis of 1% of the DNA extracted from 200 µl of serum, yielding a theoretical detection limit of 5 cells ml -1 hemolymph, assuming that 1 cell is present per sample. When applied to a limited field survey of blue crabs col- lected in Maryland coastal bays from May to August 2005, 24 of 128 crabs (18.8%) were identified as positive for Hematodinium sp. infection using qPCR. In comparison, only 6 of 128 crabs (4.7%) were identified as positive using traditional hemolymph microscopic examination. The qPCR method also detected the parasite in gill, muscle, heart and hepatopancreas tissues, with 17.2% of the crabs show- ing infection in at least one of these tissues. Importantly, it is now possible to enumerate parasites within defined quantities of crab tissue, which permits collection of more detailed information on the epizootiology of the pathogen.