Parasitic Dinoflagellate Research Articles

Dinoflagellate phylogeny revisited: Using ribosomal proteins to resolve deep branching dinoflagellate clades

The alveolates are composed of three major lineages, the ciliates, dinoflagellates, and apicomplexans. Together these ‘protist’ taxa play key roles in primary production and ecology, as well as in illness of humans and other animals. The interface between the dinoflagellate and apicomplexan clades has been an area of recent discovery, blurring the distinction between these two clades. Moreover, phylogenetic analysis has yet to determine the position of basal dinoflagellate clades hence the deepest branches of the dinoflagellate tree currently remain unresolved. Large-scale mRNA sequencing was applied to 11 species of dinoflagellates, including strains of the syndinean genera Hematodinium and Amoebophrya, parasites of crustaceans and dinoflagellates, respectively, to optimize and update the dinoflagellate tree. From the transcriptome-scale data a total of 73 ribosomal protein-coding genes were selected for phylogeny. After individual gene orthology assessment, the genes were concatenated into a >15,000 amino acid alignment with 76 taxa from dinoflagellates, apicomplexans, ciliates, and the outgroup heterokonts. Overall the tree was well resolved and supported, when the data was subsampled with gblocks or constraint trees were tested with the approximately unbiased test. The deepest branches of the dinoflagellate tree can now be resolved with strong support, and provides a clearer view of the evolution of the distinctive traits of dinoflagellates.

Genotypic variation in the parasitic dinoflagellate Hematodinium perezi along the Delmarva Peninsula, Virginia

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.

Variation in spatial and temporal incidence of the crustacean pathogen Hematodinium perezi in environmental samples from Atlantic Coastal Bays

BackgroundHematodinium 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.ResultsA 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.ConclusionsH. 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.

Development of a rapid assay to detect the dinoflagellate Amyloodinium ocellatum using loop-mediated isothermal amplification (LAMP)

Amyloodinium ocellatum is a highly pathogenic dinoflagellate parasite with global distribution that causes high mortalities in the culture of tropical and sub-tropical marine and estuarine fishes. Diagnosis typically occurs through gross examination following the onset of morbidity, at which point treatment is of limited benefit. In the present study, a new molecular diagnostic tool for the rapid detection of A. ocellatum (AO) was developed using the loop-mediated isothermal amplification method (LAMP). The AO-LAMP assay designed is highly specific using a set of four primers – two outer and two inner primers targeting six different regions on the 5′ end of the Small Subunit rDNA region (SSU rDNA) of A. ocellatum. The AO-LAMP assay, optimized for 25–30min at 62°C, amplified the DNA from A. ocellatum extracted from both water and gill tissue samples and did not amplify DNA from four closely related dinoflagellate species. The detection limit of the AO-LAMP assay was 10fg, exceptionally higher than the conventional PCR (1pg). In addition, the standardized AO-LAMP assay was capable of detecting single tomonts and trophonts; the assay was not affected by the presence of possible inhibitory substances present in environmental water samples or gill samples. The AO-LAMP assay developed in the present study provides a novel useful tool for the simple, rapid and sensitive detection of A. ocellatum in water and gill tissue samples, which could assist in the early detection and improved control of A. ocellatum infections in aquaculture systems.

The co-occurrence of Callinectes sapidus Rathbun, 1896 (Brachyura: Portunidae) and the parasitic dinoflagellate Hematodinium sp. (Dinoflagellata: Syndinidae) in two transitional water ecosystems of the Apulia coastline (South-Italy).

1 - Coastal marine and transitional water ecosystems are threatened world-wide by invasions of nonindigenous invertebrate species, altering community structure and ecosystem functioning. 2 - Here, we report on the occurrence of the Atlantic blue crab Callinectes sapidus in transitional water ecosystems of the Apulia coastline (Salento peninsula, SE Italy). 3 - Blue crabs were sampled seasonally, every three months over a whole-year period in the Torre Colimena basin (Ionian Sea) and Acquatina lagoon (Adriatic Sea). Specimens were identified and enumerated. In addition, their hemolymph was screened for parasite infections using histological techniques. 4 - Callinectes sapidus was sampled in the Torre Colimena basin, where no other crab species were collected during the whole experimental period. In contrast, in the Acquatina Lagoon four crab species were sampled, including C. sapidus. 5 - The parasitic dinoflagellate Hematodinium sp., known to determine in C. sapidus the degenerative bitter crab syndrome in its native habitats, was ubiquitously detected in the hemolymph of blue crabs from both habitats and in autochthonous brachyurans collected in the Acquatina Lagoon. 6 - An assessment of the diverse spectrum of potential ecological effects triggered by the Callinectes-Hematodinium interaction on autochthonous brachyuran species is presented, together with a preliminary evaluation of the molecular approaches to be implemented in order to verify the speciesspecificity of the host-parasite interaction.

Hematodinium infections in cultured Chinese swimming crab, Portunus trituberculatus, in northern China

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.

Molecular and functional ecology of aquatic microbial symbionts

Molecular and functional ecology of aquatic microbial symbionts

Prevalence and distribution of the dinoflagellate Thalassomyces californiensis Collard, 1966 (Ellobiopsidae) on Pasiphaea emarginata Rathbun, 1902 (Decapoda, Caridea, Pasiphaeidae), off western Mexico

A large series of 96 specimens (79 females, 13 ovigerous females, and 3 males; 1 unsexed specimen) of Pasiphaea emarginata Rathbun, 1902, was collected off western Mexico, mostly during the TALUD project aimed at the study of deep-water benthic and pelagic species. The external dinoflagellate parasite Thalassomyces californiensis Collard, 1966 (Ellobiopsidae) was observed on the eyes of 41 specimens, but was notably absent in ovigerous females (13 specimens), while it infested 45.2% of the non-ovigerous females. Two of the three males captured were infested (one with the parasite on both eyes, the other only on the left eye). In non-gravid females, the parasite was located either on the left eye (16 cases), on the right eye (18 cases) or on both eyes (4 cases). Based on the material examined, the number of known localities for Pasiphaea emarginata is increased from three to 24 and to a new southernmost limit off SW Mexico, while the records for T. californiensis are the first for the entire Gulf of California.

Phylogenetic composition and distribution of picoeukaryotes in the hypoxic northwestern coast of the Gulf of Mexico

Coastal marine hypoxic, or low-oxygen, episodes are an increasing worldwide phenomenon, but its effect on the microbial community is virtually unknown by far. In this study, the community structure and phylogeny of picoeukaryotes in the Gulf of Mexico, which are exposed to severe hypoxia in these areas was explored through a clone library approach. Both oxic surface waters and suboxic bottom waters were collected in August 2010 from three representative stations on the inner Louisiana shelf near the Atchafalaya and Mississippi River plumes. The bottom waters of the two more western stations were much more hypoxic in comparison to those of the station closest to the Mississippi River plume, which were only moderately hypoxic. A phylogenetic analysis of a total 175 sequences, generated from six 18S rDNA clone libraries, demonstrated a clear dominance of parasitic dinoflagellates from Marine alveolate clades I and II in all hypoxic waters as well as in the surface layer at the more western station closest to the Atchafalaya River plume. Species diversity was significantly higher at the most hypoxic sites, and many novel species were present among the dinoflagellate and stramenopile clades. We concluded that hypoxia in the Gulf of Mexico causes a significant shift in picoeukaryote communities, and that hypoxia may cause a shift in microbial food webs from grazing to parasitism.

Characterization and Molecular Epidemiology of a Fungal Infection of Edible Crabs (Cancer pagurus) and Interaction of the Fungus with the Dinoflagellate Parasite Hematodinium

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.

Seasonal Prevalence of Hematodinium sp. Infections of Blue Crabs in Three South Carolina (USA) Rivers

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.

Diversity analysis of protistan microplankton in Sagami Bay by 18S rRNA gene clone analysis using newly designed PCR primers

The diversity of protistan microplankton in Sagami Bay was revealed by 18S rRNA gene clone analysis using newly designed PCR primers. PCR amplification consisted of a first reaction targeting the V3–V5 region of the 18S rRNA gene, followed by a nested reaction targeting the V3–V4 region. In total, 629 clones consisting of 108 phylotypes were affiliated with a variety of protistan groups including dinoflagellates, diatoms, prymnesiomonada, chlorophyta, ciliophora, cercozoa, and heterokonta. The dinoflagellate group was detected most frequently and shared approximately 74 % of the total clones. Within this group, approximately half of the clones belonged to the parasitic dinoflagellate Syndiniales group I, which was first reported from Sagami Bay. The genera Woloszynskia, Gonyaulax, Neoceratium, and Karlodinium have not been reported from this bay until now. The second most frequent group was diatoms, which shared approximately 22 % of the total clones. Within this group, highly diverse Thalassiosira phylotypes were detected, and they shared approximately 70 % of the diatom clones. Therefore, highly diverse protists including some candidate groups were successfully detected, indicating that the designed primers and PCR protocol will be useful for molecular diversity analyses of protistan microplankton communities in aquatic environments.

Metagenomic examination of diversity within eukaryotic plankton from the ulleung basin in the East Sea of Korea

We constructed planktonic 18S rDNA clone libraries for micro-organisms in the euphotic zone of the Ulleung Basin in the East Sea of Korea. They revealed the cryptic biodiversity of eukaryotic planktons and demonstrated specific phylogenetic affiliations at certain water depths. Dinoflagellate clones dominated at the surface and 75-m depth. Members of the Syndiniales order (Groups I and II), containing wellknown parasitic dinoflagellates, as well as one their prominent hosts, Polycystinea, were found exclusively at 75 m. These observations suggest that the presence of species from Groups I and II is closely related to the specific water mass. Therefore, their metagenomics information might be useful for delineating both water-mass and physico-chemical properties.

The Effect of Salinity On Experimental Infections of A Hematodinium SP. In Blue Crabs, Callinectes sapidus

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.

Hematodinium sp. and its bacteria-like endosymbiont in European brown shrimp (Crangon crangon)

BackgroundParasitic dinoflagellates of the genus Hematodinium are significant pathogens affecting the global decapod crustacean fishery. Despite this, considerable knowledge gaps exist regarding the life history of the pathogen in vivo, and the role of free living life stages in transmission to naïve hosts.ResultsIn this study, we describe a novel disease in European brown shrimp (Crangon crangon) caused by infection with a parasitic dinoflagellate of the genus Hematodinium. This is the second example host within the Infraorder Caridea (shrimp) and significantly, the first description within the superfamily Crangonoidea. Based upon analysis of the rRNA gene (SSU) and spacers (ITS1), the parasite in C. crangon is the same as that previously described infecting Nephrops norvegicus and Cancer pagurus from European seas, and to the parasite infecting several other commercially important crab species in the Northern Hemisphere. The parasite is however distinct from the type species, H. perezi, found infecting type hosts (Carcinus maenas and Liocarcinus depurator) from nearby sites within Europe. Despite these similarities, the current study has also described for the first time, a bacteria-like endosymbiont within dinospore stages of the parasite infecting shrimp. The endosymbionts were either contained individually within electron lucent vacuoles within the parasite cell cytoplasm, or remained in direct contact with the parasite cytoplasm or in some cases, the nucleoplasm. In all of these cases, no apparent detrimental effects of colonization were observed within the parasite cell.ConclusionsThe presence of bacteria-like endosymbionts within dinospore life stages presumes that the relationship between the dinoflagellate and the bacteria is extended beyond the period of liberation of spores from the infected host shrimp. In this context, a potential role of endosymbiosis in the survival of free-living stages of the parasite is possible. The finding offers a further intriguing insight into the life history of this enigmatic pathogen of marine crustacean hosts and highlights a potential for mixotrophy in the parasitic dinoflagellates contained within the genus Hematodinium.

Lack of transmission of Hematodinium sp. in the blue crab Callinectes sapidus through cannibalism

Hematodinium spp. are parasitic dinoflagellates of marine crustaceans. Outbreaks of Hematodinium sp. have impacted commercial landings of the blue crab Callinectes sapidus in the coastal bays of Virginia and Maryland (USA), with seasonal peaks in prevalence reaching 85%. The life cycle and transmission routes of the parasite in blue crabs are poorly understood. Cannibalism and waterborne transmission may be routes of transmission, although little conclusive evidence has been reported for these modes. We examined cannibalism as a route by a series of experiments wherein we repeatedly fed adult and juvenile crabs the tissues of crabs infected with Hematodinium. In each experiment, feeding was done 3 times over the course of 1 wk. Only 2 of 120 crabs were infected within 7 to 9 d after feeding, and these 2 were likely infected prior to the experimental exposures. Crabs inoculated with hemolymph from infected donors served as positive controls. They developed infections over 11 to 21 d, indicating that the Hematodinium sp. used in the cannibalism trials was infectious at the time of inoculation. Because amphipods also harbor Hematodinium-like infections, we fed tissues of infected crabs to the estuarine amphipod Leptocheirus plumulosus. Hematodinium DNA was detected in amphipods shortly after feeding, but not in animals held for longer periods, nor was it observed in histological preparations. Amphipods did not obtain infections by scavenging infected crab tissues. Our results show that Hematodinium sp. is not effectively transmitted through ingestion of diseased tissues, indicating that cannibalism may not be a major route of transmission for Hematodinium sp. in blue crabs.

In vitro culture and developmental cycle of the parasitic dinoflagellate Hematodinium sp. from the blue crab Callinectes sapidus

Hematodinium is a genus of parasitic dinoflagellates whose species have caused significant mortalities in marine crustacean fisheries worldwide. A species of Hematodinium infects the blue crab, Callinectes sapidus on the eastern seaboard of the USA. The mode of transmission of the parasite in blue crabs is unknown. We established several continuous in vitro cultures of Hematodinium sp. isolated from the haemolymph of infected blue crabs. One isolate has been continuously maintained in our laboratory through serial subcultivation for over 12 months, and is capable of infecting new hosts when inoculated into healthy crabs. Cells of the parasite undergo characteristic developmental changes in vitro consistent with the identifiable stages of Hematodinium sp.: filamentous trophonts, amoeboid trophonts, arachnoid trophonts and sporonts, sporoblasts, prespores and dinospores (macrospores and microspores). Additionally, we describe an unusual shunt in the life cycle wherein presumptive schizonts derived from arachnoid sporonts developed into filamentous and arachnoid trophonts that can then initiate arachnoid sporonts in new cultures. This may explain the rapid proliferation of the parasite in blue crab hosts. We also found that temperature and light intensity affected the growth and development of the parasite in vitro.

The Role of Alternate Hosts in the Ecology and Life History of Hematodinium sp., a Parasitic Dinoflagellate of the Blue Crab (Callinectes sapidus)

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.

Susceptibility and Tolerance of Spotted Seatrout, Cynoscion nebulosus, and Red Snapper, Lutjanus campechanus, to Experimental Infections with Amyloodinium ocellatum

Amyloodinium ocellatum is a parasitic dinoflagellate that infects warm-water marine and estuarine fishes and causes mortalities in aquaculture. Its life cycle consists of 3 stages: a feeding trophont that parasitizes the gills and skin where it interferes with gas exchange, osmoregulation, and tissue integrity; a detached reproductive tomont; and a free-swimming infective dinospore. We compared the susceptibility and tolerance of juvenile spotted seatrout, Cynoscion nebulosus, and red snapper, Lutjanus campechanus, to this parasite by individually exposing fish in 3-L aquaria (at 25 C and 33 practical salinity units) to several dinospore doses over different time periods and quantified the size and number of resulting trophonts. We estimated the trophont detachment rate and trophont size at detachment, the 24-hr dinospore infection rate, the dinospore 48-hr median lethal dose (LD(50)), and the trophont lethal load at the 48-hr LD(50). There were no significant differences in dinospore infection rates or dinospore lethal doses between spotted seatrout and red snapper; however, trophonts remained attached longer and attained a larger size in red snapper than in spotted seatrout. The trophont lethal load was significantly higher in spotted seatrout than in red snapper. A proposed model simulating the trophont dynamics reflected our experimental findings and showed that A. ocellatum reproductive success is linked both to the number of dinospores and the size of the trophont, factors that, in turn, are linked to the time the trophont spends on the host and the number of trophonts the host can tolerate.

Sources of variability in prevalence and distribution of bitter crab disease in snow crab (Chionoecetes opilio) along the northeast coast of Newfoundland

AbstractMullowney, 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.