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A recent population collapse of eastern Bering Sea (EBS) snow crab (Chionoecetes opilio) led to the first-ever closure of the snow crab fishery in 2022. The population collapse, caused, in part, by unprecedented warming, was preceded by peaks in juvenile snow crab density (2018) and bitter crab disease (BCD, Hematodinium sp.; 2016), a fatal crustacean disease. Annual bottom trawl surveys in the EBS show high year-to-year spatiotemporal variation in BCD-infected crab, yet it remains unclear what ecological drivers might explain the variation. We used statistical models of BCD presence/absence to examine the relative importance of intrinsic and extrinsic factors as drivers of BCD. We found a dome-shaped relationship between temperature and BCD presence, and results suggest that 2–4°C bottom temperatures are more likely to support BCD. Matching with past work across the globe, we find that stations with high population density of small, new shell crab are most likely to be BCD-positive. While our work highlights the challenges of disease monitoring in the EBS, our results indicate that indirect management measures related to snow crab rebuilding and recruitment may be more appropriate than directed fisheries management in mitigating BCD impacts. [ABSTRACT FROM AUTHOR]

Parasitic dinoflagellates of the genus Hematodinium are known to infect various marine crustaceans worldwide, especially crabs and several species of shrimp and lobster. Some of these species are new host species and components of commercial fishery products. These parasitic species are predominantly found in the hemolymph of the host and cause pathological changes and functional damage to organs and tissues, leading to death. In recent years, these parasites have infected important commercially valuable species, particularly in European waters, US waters, Australian waters, and recently in Shandong Peninsula in China. These Hematodinium pathogens were also reported to affect wild shrimp in Chinese waters and in the English North Sea. These rapid spreads affect crustacean aquaculture industries, where they are indeed a significant threat to the sustainability of the aquaculture of important crustaceans. The fishery products industries are also under pressure from the invasion of this pathogen, as the crab meat produced has a bitter taste, which may reduce its marketability. In response to these threats, this review was aimed at providing a broader understanding of the development of parasite distribution and ecological aspects of Hematodinium. In addition, the interaction of these pathogens with their hosts, the environmental drivers of Hematodinium disease, and future research perspectives were discussed. [ABSTRACT FROM AUTHOR]

From October 2020 to September 2021, researchers examined various facets of the reproductive biology of male Portunus segnis crabs caught in the fishing port of the Great Bitter Lake on Egypt's Suez Canal coast. The male reproductive system of P. segnis consists of two testes, a commissure, two vas deferentia, and two ejaculatory ducts internally. It is bilaterally symmetrical and creamy to whitish in appearance. The three components of the vas deferentia were the anterior vas deferens (AVD), median vas deferens (MVD) and posterior vas deferens (PVD). There are three stages of male gonad development: Immature, maturing and mature. For light microscopic examinations, tissues from the testis, (AVD), (MVD), (PVD) and ejaculatory duct were fixed in Bouin's solution. The blue swimming crab P. segnis is an important host of parasitic dinoflagellates from the genus Hematodinium. The commercial supply of P. segnis has been harmed by outbreaks of these parasites. Hematodinium perezi, a dinoflagellate, had no discernible impact on the gonad growth and development of its host Portunus segnis. For uninfected and infected males, the size at first sexual maturity was estimated to be 66.3 and 67.3 mm carapace width (CW), respectively. [ABSTRACT FROM AUTHOR]

The parasitic dinoflagellates of the genus Hematodinium have been considered one of the most important emerging pathogens for a broad range of marine crustaceans around the world. In China, frequent outbreaks of Hematodinium infections have caused serious economic losses for local farmers since 2004. Wild crabs were recently indicated to play a vital role in the transmission and spreading of the Hematodinium disease in polyculture pond systems. Based on PCR amplification and histopathological examination, we demonstrated that H. perezi can naturally infect a wild crab species, Hemigrapsus takanoi, which were collected from the waterways located on the coast of Rizhao or Weifang, Shandong Peninsula, China. According to the sequence similarity analysis and phylogenetic analysis, the Hematodinium isolates were identified as H. perezi and belonged to genotype II. The prevalence of H. perezi ranged from 3.3% to 5.7% in H. takanoi originating from Rizhao (n = 165 wild crabs) and from 0.9% to 20.0% in that originating from Weifang (n = 1386 wild crabs), respectively. To our knowledge, H. takanoi is, for the first time, reported as a new host for Hematodinium. Given the wide distribution of H. takanoi on the coasts along the Shandong Peninsula and the relative high prevalence of infection we monitored in our study, we speculate that H. takanoi contributes to the introducing and spreading parasitic Hematodinium between ponds via waterways in a poly‐culturing system. Findings in this study broaden the host range of this parasite and expand the scope of our surveillance for Hematodinium disease in China. [ABSTRACT FROM AUTHOR]

Parasitic dinoflagellates in genus Hematodinium have caused substantial economic losses to multiple commercially valuable marine crustaceans around the world. 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 the comprehensive omics approaches (miRNA transcriptomics, iTRAQ-based proteomics) to get insights into the host-parasite interaction between hemocytes from Portunus trituberculatus and Hematodinium perezi in the present study. The parasitic dinoflagellate H. perezi 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 and peroxisome pathways. Cellular structure and communication was seriously impacted by post-transcriptional downregulation of ECM-receptor interaction and focal adhesion pathways. In conclusion, H. perezi parasites could trigger striking changes in the miRNome and proteome of crustacean hemocytes, and this parasite exhibited multifaceted immunomodulatory effects and potential immune-suppressive mechanisms in crustacean hosts. • Hematodinium perezi triggered striking changes in miRNome and proteome of Portunus trituberculatus hemocytes. • A total of 44 miRNAs and 523 proteins were differentially expressed in P. trituberculatus after H. perezi challenge. • H. perezi exhibited multifaceted immunomodulatory effects and potential immune-suppressive mechanisms in crustacean hosts. [ABSTRACT FROM AUTHOR]

Tanner crab (Chionoecetes bairdi) is 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 provide a transcriptomic resource for the Tanner crab, we generated a suite of RNA-seq libraries encompassing pooled hemolymph samples from crab displaying differing infection statuses and maintained at different temperatures (ambient (7.5˚C), elevated (10˚C), or decreased (4˚C)). 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 RNA-seq 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 that 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. [ABSTRACT FROM AUTHOR]

Abstract 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

Abstract 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. Graphical abstract Unlabelled Image Highlights • 905 proteins were identified in Portunus trituberculatus hepatopancreas with the iTRAQ approach. • 392 differentially expressed proteins were quantified using iTRAQ labelling after Hematodinium challenge. • GO, COG and KEGG enrichment analysis of the identified and differentially expressed proteins were conducted. • Hematodinium could cause immune-suppressive and detrimental effects on the immunity in crustacean hepatopancreas. [ABSTRACT FROM AUTHOR]

Parasitic dinoflagellates of the genus Hematodinium are known to infect various marine crustaceans worldwide, especially crabs and several species of shrimp and lobster. Some of these species are new host species and components of commercial fishery products. These parasitic species are predominantly found in the hemolymph of the host and cause pathological changes and functional damage to organs and tissues, leading to death. In recent years, these parasites have infected important commercially valuable species, particularly in European waters, US waters, Australian waters, and recently in Shandong Peninsula in China. These Hematodinium pathogens were also reported to affect wild shrimp in Chinese waters and in the English North Sea. These rapid spreads affect crustacean aquaculture industries, where they are indeed a significant threat to the sustainability of the aquaculture of important crustaceans. The fishery products industries are also under pressure from the invasion of this pathogen, as the crab meat produced has a bitter taste, which may reduce its marketability. In response to these threats, this review was aimed at providing a broader understanding of the development of parasite distribution and ecological aspects of Hematodinium. In addition, the interaction of these pathogens with their hosts, the environmental drivers of Hematodinium disease, and future research perspectives were discussed., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

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. [ABSTRACT FROM AUTHOR]

In the blue crab, Callinectes sapidus, early studies suggested a relationship between smaller crabs, which molt more frequently, and higher rates of infection by the dinoflagellate parasite, Hematodinium perezi. In order to better explore the influence of size and molting on infections, blue crabs were collected from the Maryland coastal bays and screened for the presence of H. perezi in hemolymph samples using a quantitative PCR assay. Molt stage was determined by a radioimmunoassay which measured ecdysteroid concentrations in blue crab hemolymph. Differences were seen in infection prevalence between size classes, with the medium size class (crabs 61 to 90 mm carapace width) and juvenile crabs (≤ 30 mm carapace width) having the highest infection prevalence at 47.2% and 46.7%, respectively. All size classes were susceptible to infection, although fall months favored disease acquisition by juveniles, whereas mid-sized animals (31–90 mm carapace width) acquired infection predominantly in summer. Disease intensity was also most pronounced in the summer, with blue crabs > 61 mm being primary sources of proliferation. Molt status appeared to be influenced by infection, with infected crabs having significantly lower concentrations of ecdysteroids than uninfected crabs in the spring and the fall. We hypothesize that infection by H. perezi may increase molt intervals, with a delay in the spring molt cycle as an evolutionary adaptation functioning to coincide with increased host metabolism, providing optimal conditions for H. perezi propagation. Regardless of season, postmolt crabs harbored significantly higher proportions of moderate and heavy infections, suggesting that the process of ecdysis, and the postmolt recovery period, has a positive effect on parasite proliferation. [ABSTRACT FROM AUTHOR]

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 naïve 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. [ABSTRACT FROM AUTHOR]

The parasitic dinoflagellate, Hematodinium perezi , negatively impacts the commercially important blue crab, Callinectes sapidus . The parasite is a host generalist, but it has not been reported from littoral fiddler crabs living within a few meters of habitat known to harbor infected blue crabs. In the first study, populations of three species of fiddler crab were screened for natural infections. The infection status of field-collected and lab-inoculated crabs was determined by screening fresh hemolymph with a 0.3% neutral red solution. Fiddler crabs were collected by hand in an area adjacent to where infected blue crabs were commonly collected. None of the 431 fiddlers had natural infections. In two separate studies, three species of fiddler crabs, Uca minax , U. pugnax , and U. pugilator , were evaluated for their susceptibility to H. perezi via inoculation of trophic stages. Uca minax inoculated with 10,000 cells of H. perezi were monitored for progression of the parasite. During hemolymph screenings of disease progression, filamentous trophonts, ameboid trophonts, and clump colonies were observed, indicative of active infections. In the second study, the minimum infective dose in U. minax was investigated. Fiddler crabs were inoculated with 0, 100, 1000, or 10,000 cells per crab. The minimum dose was determined to be approximately 1000 ameboid trophonts per crab. All three species of fiddler crab were susceptible to H. perezi via inoculation. The parasite was serially transferred from fiddler crabs to blue crabs without loss of infectivity. Survival studies indicated similar progression patterns to those observed in blue crabs. Based on our results fiddler crabs can serve as a laboratory model for investigating H. perezi infections and may be useful for comparative studies with blue crabs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Increasing evidences have established that the nitric oxide synthase (NOS) and NADPH oxidase (NOX) play important roles in host defense system by catalyzing the production of nitrogen oxide (NO) and superoxide anions (O 2 − ), respectively. While, there are limited studies to explore the roles of NOS/NOX enzymes in crustacean immunity, and no studies as yet were attempted to elucidate their functions in host immune responses to parasites. In the present study, we cloned a full-length cDNA of NOS and two partial cDNA fragments of NOX and GPx from the economic valuable crab Portunus trituberculatus . The full-length cDNA of NOS was 4002 bp in length that encoded 1203 amino acids containing motifs of the NOS protein and conserved domains. The phylogenetic analysis showed that the NOS protein sequence was clustered together with those of crustacean species in the phylogenetic tree. All of the three novel genes showed high mRNA transcripts in the immune-related tissues (e.g. hemocytes, hepatopancreas) of P. trituberculatus . Striking fluctuation in the transcripts of the critical NO/O 2 − - generating/scavenging related genes ( NOS , NOX , CuZnSOD , CAT , GPx ) as well as in the enzymatic activities of NOS, NOX, SOD, CAT and GPx were observed in the hemocytes and hepatopancreas of P . trituberculatus post challenged with the parasitic dinoflagellate Hematodinium , indicating that the NO/O 2 − - generating and the antioxidant systems played vital roles in the crustacean innate immunity against the parasitic intrusion. The results indicated a novel respect of the host-parasite interaction between the crab host and the parasitic dinoflagellate Hematodinium . [ABSTRACT FROM AUTHOR]

Tolls/Toll-like receptors (TLRs) are important cell-surface receptors serving as pattern recognition receptors (PRRs) in the Tolls/TLRs signaling pathway of innate immune responses. In the present study, we isolated and characterized a novel Toll gene ( PtToll ) from Portunus trituberculatus , and further investigated its expression in various tissues of crab hosts challenged with the parasitic dinoflagellate Hematodinium . The full-length cDNA of PtToll was 3745 bp, with a 3012 bp open reading frame (ORF) encoding 1003 amino acids. Conserved domains consist of 15 tandem leucine-rich repeats (LRRs), a single-pass transmembrane segment (TM) and a cytoplasmic Toll/interleukin-1R (TIR) domain. The PtToll protein shared high similarity to other crustacean Tolls and was clustered with the crustacean Tolls in the phylogenetic tree. The PtToll gene was constitutively expressed in various tissues of P. trituberculatus , with the highest expression in hemocytes. After being challenged with the parasite, the transcripts of PtToll reacted immediately with significant alterations in all the tested tissues, and decreased consistently in most of the detected tissues (e.g., hemocytes, gill, heart, and muscle) within 24 h. Then the transcripts of PtToll were significantly up-regulated in hemocytes and heart at 48 h, and in hepatopancreas at 48 and 96 h post the parasitic challenge. By 192 h post challenge, the transcriptional level of PtToll indicated a significant suppression or a decreasing trend. The fluctuations of PtToll gene expression suggested that PtToll was closely associated with intrusion of the Hematodinium parasites, and may possess a vital and systematic function in the innate immunity of P. trituberculatus against the parasitic infection. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 8–12 days. 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. [ABSTRACT FROM AUTHOR]

The prevalence of disease in edible crabs ( Cancer pagurus ) was assessed at two sites in South West Wales; one estuarine (Pembroke Ferry) and another facing open water (Freshwater East). Diseases included pink crab disease caused by Hematodinium sp., an infection of the antennal gland caused by Paramikrocytos canceri and an idiopathic inflammatory condition of the connective tissue surrounding the anterior ganglionic masses. This latter condition was only found in crabs from Pembroke Ferry. There was a significantly higher prevalence of pink crab disease at Freshwater East than Pembroke Ferry, although both sites had similar levels of infection by P . canceri . [ABSTRACT FROM AUTHOR]

Hematodinium spp. infect over 40 species of crustaceans worldwide, but have not been reported to infect the European lobster, Homarus gammarus . In this study, Hematodinium parasites (a mixture of uni- and multinucleate trophont-like stages) were taken from donor crabs ( Cancer pagurus ) and injected into juvenile H. gammarus . Juvenile C. pagurus were also injected with the same inoculum. Haemolymph was taken at regular intervals and examined for the presence of Hematodinium using light microscopy and PCR, in two separate experiments of duration 4 and 8 months. All lobsters were negative for Hematodinium whilst the C . pagurus challenged became infected. It is concluded that European lobsters are not susceptible to infection with a clade of Hematodinium that infects C. pagurus . [ABSTRACT FROM AUTHOR]

The article discusses the relationship of species of marine crustaceans as hosts to dinoflagellates of the genus Hematodinium. Topics discussed include the impact of Hematodinium parasitism on crustacean fisheries and aquaculture, the pathology of Hematodinium infection in crustacean hosts, and the effect of Hematodinium on the phagocytes of Necora norvegicus. The mechanisms used by Hematodinum to weaken, avoid recognition and eliminate the immune system of hosts are described.

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Hematodinium perezi (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. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Background: Hematodinium perezi, a parasitic dinoflagellate, infects and kills blue crabs, Callinectes sapidus, along the Atlantic and Gulf coasts of the United States. The parasite proliferates within host hemolymph and tissues, and also produces free-swimming biflagellated dinospores that emerge from infected crabs. Infections in C. sapidus recur annually, and it is not known if biotic or environmental reservoirs contribute to reinfection and outbreaks. To address this data gap, a quantitative PCR assay based on the internal transcribed spacer 2 (ITS2) region of H. perezi rRNA genes was developed to asses the temporal and spatial incidence of the parasite in Delaware and Maryland coastal bays. Results: A previously-used PCR assay for H. perezi, based on the small subunit rRNA gene sequence, was found to lack adequate species specificity to discriminate non-Hematodinium sp. dinoflagellate species in environmental samples. A new ITS2-targeted assay was developed and validated to detect H. perezi DNA in sediment and water samples using E. coli carrying the H. perezi rDNA genes. Application of the method to environmental samples identified potential hotspots in sediment in Indian River Inlet, DE and Chincoteague Bay, MD and VA. H. perezi DNA was not detected in co-occurring shrimp or snails, even during an outbreak of the parasite in C. sapidus. Conclusions: H. perezi is present in water and sediment samples in Maryland and Delaware coastal bays from April through November with a wide spatial and temporal variability in incidence. Sampling sites with high levels of H. perezi DNA in both bays share characteristics of silty, organic sediments and low tidal currents. The environmental detection of H. perezi in spring, ahead of peak prevalence in crabs, points to gaps in our understanding of the parasite's life history prior to infection in crabs as well as the mode of environmental transmission. To better understand the H. perezi life cycle will require further monitoring of the parasite in habitats as well as hosts. Improved understanding of potential environmental transmission to crabs will facilitate the development of disease forecasting. [ABSTRACT FROM AUTHOR]

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 dade 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 dinofiagellate 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The sister phyla dinoflagellates and apicomplexans inherited a drastically reduced mitochondrial genome (mitochondrial DNA, mtDNA) containing only three protein-coding (cob, cox1, and cox3) genes and two ribosomal RNA (rRNA) genes. In apicomplexans, single copies of these genes are encoded on the smallest known mtDNA chromosome (6 kb). In dinoflagellates, however, the genome has undergone further substantial modifications, including massive genome amplification and recombination resulting in multiple copies of each gene and gene fragments linked in numerous combinations. Furthermore, protein-encoding genes have lost standard stop codons, trans-splicing of messenger RNAs (mRNAs) is required to generate complete cox3 transcripts, and extensive RNA editing recodes most genes. From taxa investigated to date, it is unclear when many of these unusual dinoflagellate mtDNA characters evolved. To address this question, we investigated the mitochondrial genome and transcriptome character states of the deep branching dinoflagellate Hematodinium sp. Genomic data show that like later-branching dinoflagellates Hematodinium sp. also contains an inflated, heavily recombined genome of multicopy genes and gene fragments. Although stop codons are also lacking for cox1 and cob, cox3 still encodes a conventional stop codon. Extensive editing of mRNAs also occurs in Hematodinium sp. The mtDNA of basal dinoflagellate Hematodinium sp. indicates that much of the mtDNA modification in dinoflagellates occurred early in this lineage, including genome amplification and recombination, and decreased use of standard stop codons. Trans-splicing, on the other hand, occurred after Hematodinium sp. diverged. Only RNA editing presents a nonlinear pattern of evolution in dinoflagellates as this process occurs in Hematodinium sp. but is absent in some later-branching taxa indicating that this process was either lost in some lineages or developed more than once during the evolution of the highly unusual dinoflagellate mtDNA. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

The parasitic dinoflagellate Hematodinium sp. parasitizes blue crabs along the Atlantic seaboard of the United States. Infections in blue crabs have only been reported from waters where salinity is >11 practical salinity units (psu). Blue crabs maintain a hyperosmotic internal concentration at low salinities (0-5 psu), roughly comparable to 24 psu, and should be capable of maintaining an infection in low-salinity waters even if Hematodinium spp. cells are intolerant of low salinities. We tested this notion by observing the effect of low salinity on the progression of disease in crabs experimentally infected with the parasite. Blue crabs were acclimated to 5 psu or 30 psu salinity treatments. They were inoculated with Hematodinium sp. and necropsied 3, 7, 10, and 15 days post-inoculation. The low-salinity treatment did not have an effect on the proliferation of Hematodinium sp. infections in blue crabs; moreover, a greater proportion of infections in crabs in the low-salinity treatment developed dinospore stages than did those in the high-salinity treatment, indicating that salinity may affect the development of the parasite. However, dinospores from in vitro cultures rapidly became inactive when held in salinities <15 psu. Our experiments indicate that Hematodinium spp. can develop in blue crabs at low salinities, but that the parasite is incapable of transmission in this environment, which explains the lack of natural infections in crabs at low salinities. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Hematodinium perezi Chatton and Poisson 1931 (Dinophyceae: Syndiniales) is reported from one of its type hosts, Liocarcinus depurator, from Rye Bay in the English Channel, a site in a similar geographical location to that of the type description. The histology and ultrastructure of vegetative trophont stages, and rDNA sequences of the parasite infecting this host are reported for the first time. Ultrastructurally, H. perezi was confirmed by the presence of condensed chromatin profiles, trichocysts, an alveolar membrane, and micropores. The pathology of H. perezi was similar to other Hematodinium descriptions with large numbers of parasites present within the haemolymph and host tissues. No host responses against the parasite were observed. Molecular analysis of the ITS rRNA regions from H. perezi infecting L. depurator suggests that Callinectes sapidus from the United States, and Portunus trituberculatus and Scylla serrata from China are infected with different genotypes of H. perezi. The morphological and molecular characterization of H. perezi in one of the type hosts from Europe will allow for a better understanding of the phylogeny of these pathogens of commercially important Crustacea. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]