Large-scale variation in wave attenuation of oyster reef living shorelines and the influence of inundation duration.

One of the paramount goals of oyster reef living shorelines is to achieve sustained and adaptive coastal protection, which requires meeting ecological (i.e., develop a self-sustaining oyster population) and engineering (i.e., provide coastal defense) targets. In a large-scale comparison along the Atlantic and Gulf coasts of the United States, the efficacy of various designs of oyster reef living shorelines at providing wave attenuation was evaluated accounting for the ecological limitations of oysters with regard to inundation duration. A critical threshold for intertidal oyster reef establishment is 50% inundation duration. Living shorelines that spent less than one-half of the time (<50%) inundated were not considered suitable habitat for oysters, however, were effective at wave attenuation (68% reduction in wave height). Reefs that experienced >50% inundation were considered suitable habitat for oysters, but wave attenuation was similar to controls (no reef; ~5% reduction in wave height). Many of the oyster reef living shoreline approaches therefore failed to optimize the ecological and engineering goals. In both inundation regimes, wave transmission decreased with an increasing freeboard (difference between reef crest elevation and water level), supporting its importance in the wave attenuation capacity of oyster reef living shorelines. However, given that the reef crest elevation (and thus freeboard) should be determined by the inundation duration requirements of oysters, research needs to be refocused on understanding the implications of other reef parameters (e.g., width) for optimizing wave attenuation. A broader understanding of the reef characteristics and seascape contexts that result in effective coastal defense by oyster reefs is needed to inform appropriate design and implementation of oyster-based living shorelines globally.

Unusually abundant and large ciliate xenomas in oysters, Crassostrea virginica, from Great Bay, New Hampshire, USA.

During routine histological examination of oysters (Crassostrea virginica) from Great Bay, New Hampshire, USA, a high prevalence and intensity of ciliate xenomas has been noted since sampling began in 1997. Xenomas are hypertrophic lesions on the gills of bivalve molluscs caused by intracellular ciliates, likely Sphenophrya sp. Although not known to cause mortality in oysters, xenomas have not previously been reported at this high abundance. The objectives of this study were to characterize the xenomas, describe the ciliates, and gather baseline epizootiological data with correlations to environmental and biological parameters. Upon gross examination, xenomas appeared as white nodules, up to 3mm in diameter, located in the gill tissue and occasionally fusing into large masses along the gill filaments. Light microscopy of histological sections revealed xenomas located in the gill water tubes, which they often completely blocked. Higher magnification revealed dual nuclei, eight kineties, and conjugation of the ciliates. Transmission electron microscopy revealed dual nuclei that varied in density, a maximum of twenty cilia in each kinety radiating from the oral apparatus to the posterior, and a 9+2 axoneme structure within the cilia. These traits place the ciliates into the Order Rhynchodida, but insufficient molecular data exist to confirm classification of this ciliate to the Genus Sphenophrya. Since 1997, xenoma prevalence has fluctuated with peaks in 2000, 2004, and 2011. Infected oysters generally contained <30 xenomas, but 2.1% contained >100, sharply contrasting the rare prevalence and low intensity reported elsewhere. Prevalence increased with oyster size, leveling off near 50% in oysters >60mm. Infection intensity peaked in 70-90mm oysters and declined in larger oysters. Individual oyster condition was not associated with xenoma intensity, but sites with oysters in higher condition generally had a greater prevalence and intensity of xenoma infections. Seasonal data indicated an infection cycle increasing from summer to fall, peaking at 55-65% in November and dropping to <10% by spring. The oyster population in Great Bay, NH warrants further examination to understand the mechanisms and conditions controlling xenoma formation.

Development and applications of Ray's fluid thioglycollate media for detection and manipulation of Perkinsus spp. pathogens of marine molluscs.

During the early 1950s, Sammy M. Ray discovered that his high-salt modification of fluid thioglycollate sterility test medium caused dramatic in vitro enlargement of Perkinsus marinus (=Dermocystidium marinum) cells that coincidentally infected several experimentally cultured oyster gill tissue explants. Subsequent testing confirmed that the enlarged cells among some oyster tissues incubated in Ray's fluid thioglycollate medium (RFTM) were those of that newly described oyster pathogen. Non-proliferative in vitro enlargement, cell wall thickening, and subsequent blue-black iodine-staining of hypertrophied trophozoites (=hypnospores=prezoosporangia) following incubation in RFTM are unique characteristics of confirmed members of the protistan genus Perkinsus. A number of in vitro assays and manipulations with RFTM have been developed for selective detection and enumeration of Perkinsus sp. cells in tissues of infected molluscs, and in environmental samples. RFTM-enlarged Perkinsus sp. cells from tissues of infected molluscs also serve as useful inocula for initiating in vitro isolate cultures, and cells of several Perkinsus spp. from both in vitro cultures and infected mollusc tissues may be induced to zoosporulate by brief incubations in RFTM. DNAs from RFTM-enlarged Perkinsus sp. cells provide useful templates for PCR amplifications, and for sequencing and other assays to differentiate and identify the detected Perkinsus species. We review the history and components of fluid thioglycollate and RFTM media, and the characteristics of numerous RFTM-based diagnostic assays that have been developed and used worldwide since 1952 for detection and identification of Perkinsus spp. in host mollusc tissues and environmental samples. We also review applications of RFTM for in vitro manipulations and purifications of Perkinsus sp. pathogen cells.

Parasite transmission through suspension feeding.

Suspension-feeding bivalve molluscs are confronted with a wide range of materials in the benthic marine environment. These materials include various sized plankton and the organic material derived from it, macroalgae, detritus and a diversity of microbial parasites that have adapted life stages to survive in the water column. For bivalve parasites to infect hosts though, they must first survive and remain infectious in the water column to make initial contact with hosts, and once in contact, enter and overcome elaborate pathways for particle sorting and selection. Even past these defenses, bivalve parasites are challenged with efficient systems of mechanical and chemical digestion and highly evolved systems of innate immunity. Here we review how bivalve parasites evade these hurdles to complete their life cycles and establish within bivalve hosts. We broadly cover significant viral, bacterial, and protozoan parasites of marine bivalve molluscs, and illustrate the emergent properties of these host-parasite systems where parasite transmission occurs through suspension feeding.

Development and Evaluation of High-Density SNP Arrays for the Eastern Oyster Crassostrea virginica.

The eastern oyster Crassostrea virginica is a major aquaculture species for the USA. The sustainable development of eastern oyster aquaculture depends upon the continued improvement of cultured stocks through advanced breeding technologies. The Eastern Oyster Breeding Consortium (EOBC) was formed to advance the genetics and breeding of the eastern oyster. To facilitate efficient genotyping needed for genomic studies and selection, the consortium developed two single-nucleotide polymorphism (SNP) arrays for the eastern oyster: one screening array with 566K SNPs and one breeders' array with 66K SNPs. The 566K screening array was developed based on whole-genome resequencing data from 292 oysters from Atlantic and Gulf of Mexico populations; it contains 566,262 SNPs including 47K from protein-coding genes with a marker conversion rate of 48.34%. The 66K array was developed using best-performing SNPs from the screening array, which contained 65,893 oyster SNPs including 22,984 genic markers with a calling rate of 99.34%, a concordance rate of 99.81%, and a much-improved marker conversion rate of 92.04%. Null alleles attributable to large indels were found in 13.1% of the SNPs, suggesting that copy number variation is pervasive. Both arrays provided easy identification and separation of selected stocks from wild progenitor populations. The arrays contain 31 mitochondrial SNPs that allowed unambiguous identification of Gulf mitochondrial genotypes in some Atlantic populations. The arrays also contain 756 probes from 13 oyster and human pathogens for possible detection. Our results show that marker conversion rate is low in high polymorphism species and that the two-step process of array development can greatly improve array performance. The two arrays will advance genomic research and accelerate genetic improvement of the eastern oyster by delineating genetic architecture of production traits and enabling genomic selection. The arrays also may be used to monitor pedigree and inbreeding, identify selected stocks and their introgression into wild populations, and assess the success of oyster restoration.

Widespread survey finds no evidence of Haplosporidium nelsoni (MSX) in Gulf of Mexico oysters.

The advent of molecular detection assays has provided a set of very sensitive tools for the detection of pathogens in marine organisms, but it has also raised problems of how to interpret positive signals that are not accompanied by visual confirmation. PCR-positive results have recently been reported for Haplosporidium nelsoni (MSX), a pathogen of the oyster Crassostrea virginica in 31 of 40 oysters from 6 sites in the Gulf of Mexico and the Caribbean Sea. Histological confirmation of the PCR results was not undertaken, and no haplosporidian has been reported from the numerous histological studies and surveys of oysters in the region. To further investigate the possibility that H. nelsoni is present in this region, we sampled 210 oysters from 40 sites around the Gulf of Mexico and Puerto Rico using PCR and 180 of these using tissue-section histology also. None of the oysters showed evidence of H. nelsoni by PCR or of any haplosporidian by histology. We cannot, therefore, confirm that H. nelsoni is present and widespread in the Gulf of Mexico and the Caribbean Sea. Our results do not prove that H. nelsoni is absent from the region, but taken together with results from previous histological surveys, they suggest that for the purposes of controlling oyster importation, the region should continue to be considered free of the parasite.

Transcriptomic Response to Perkinsus marinus in Two Crassostrea Oysters Reveals Evolutionary Dynamics of Host-Parasite Interactions.

Infectious disease outbreaks are causing widespread declines of marine invertebrates including corals, sea stars, shrimps, and molluscs. Dermo is a lethal infectious disease of the eastern oyster Crassostrea virginica caused by the protist Perkinsus marinus. The Pacific oyster Crassostrea gigas is resistant to Dermo due to differences in the host-parasite interaction that is not well understood. We compared transcriptomic responses to P. marinus challenge in the two oysters at early and late infection stages. Dynamic and orchestrated regulation of large sets of innate immune response genes were observed in both species with remarkably similar patterns for most orthologs, although responses in C. virginica were stronger, suggesting strong or over-reacting immune response could be a cause of host mortality. Between the two species, several key immune response gene families differed in their expansion, sequence variation and/or transcriptional response to P. marinus, reflecting evolutionary divergence in host-parasite interaction. Of note, significant upregulation of inhibitors of apoptosis (IAPs) was observed in resistant C. gigas but not in susceptible C. virginica, suggesting upregulation of IAPs is an active defense mechanism, not a passive response orchestrated by P. marinus. Compared with C. gigas, C. virginica exhibited greater expansion of toll-like receptors (TLRs) and positive selection in P. marinus responsive TLRs. The C1q domain containing proteins (C1qDCs) with the galactose-binding lectin domain that is involved in P. marinus recognition, were only present and significantly upregulated in C. virginica. These results point to previously undescribed differences in host defense genes between the two oyster species that may account for the difference in susceptibility, providing an expanded portrait of the evolutionary dynamics of host-parasite interaction in lophotrochozoans that lack adaptive immunity. Our findings suggest that C. virginica and P. marinus have a history of coevolution and the recent outbreaks may be due to increased virulence of the parasite.

Microarray analysis of gene expression in eastern oyster (Crassostrea virginica) reveals a novel combination of antimicrobial and oxidative stress host responses after dermo (Perkinsus marinus) challenge.

Dermo disease, caused by Perkinsus marinus, is one of the most severe diseases of eastern oysters, Crassostrea virginica. It causes serious mortalities in both wild and aquacultured oysters. Using existing expressed sequence tag (EST) resources, we developed a 12K in situ oligonucleotide microarray and used it for the analysis of gene expression profiles of oysters during the interactions between P. marinus and its oyster host. Significant gene expression regulation was found at day 30 post-challenge in the eastern oyster. Putative identities of the differentially expressed genes revealed a set of genes involved in several processes including putative antimicrobial defenses, pathogen recognition and uptake, anti-oxidation and apoptosis. Consistent with results obtained from previous, smaller-scale experiments, expression profiles revealed a large set of genes likely involved in an active mitigating response to oxidative stress and apoptosis induced by P. marinus. Additionally, a unique galectin from C. virginica, CvGal, which serves as a preferential receptor for P. marinus trophozoites, was found to be significantly down-regulated in gill tissue of oysters with both light and heavy infection, suggesting an attempt to control parasite uptake and proliferation in the later stages of infection. Potential histone-derived antimicrobial responses to P. marinus were also revealed in the gene expression profiles.

From Farm to Fingers: an Exploration of Probiotics for Oysters, from Production to Human Consumption.

Oysters hold a unique place within the field of aquaculture as one of the only organisms that is regularly shipped live to be consumed whole and raw. The microbiota of oysters is capable of adapting to a wide range of environmental conditions within their dynamic estuarine environments; however, human aquaculture practices can challenge the resilience of this microbial community. Several discrete stages in oyster cultivation and market processing can cause disruption to the oyster microbiota, thus increasing the possibility of proliferation by pathogens and spoilage bacteria. These same pressure points offer the opportunity for the application of probiotics to help decrease disease occurrence in stocks, improve product yields, minimize the risk of shellfish poisoning, and increase product shelf life. This review provides a summary of the current knowledge on oyster microbiota, the impact of aquaculture upon this community, and the current status of oyster probiotic development. In response to this biotechnological gap, the authors highlight opportunities of highest potential impact within the aquaculture pipeline and propose a strategy for oyster-specific probiotic candidate development.

Minchinia mercenariae n. sp. (Haplosporidia) in the hard clam Mercenaria mercenaria: implications of a rare parasite in a commercially important host.

During routine histopathology of 180 juvenile hard clams, Mercenaria mercenaria, from a site in Virginia, USA, in 2007, we discovered a single individual heavily infected with a parasite resembling a haplosporidian, some members of which cause lethal bivalve diseases. Scanning electron microscopy of spores and sequencing of small subunit ribosomal DNA confirmed a new species: Minchinia mercenariae n. sp. Further sampling of clams at the site found prevalences up to 38% using polymerase chain reaction (PCR). No parasites were found in routine histological screening of the same individuals, but re-examination of clams judged positive by in situ hybridization (ISH) revealed very faintly staining plasmodia. No unusual mortalities have occurred among the sampled groups. Analysis of clams from Massachusetts to Florida by PCR failed to detect the parasite, but a haplosporidian found in a clam from New Jersey in 2001 was subsequently identified by ISH as M. mercenariae. No other haplosporidians have been reported in thousands of hard clams from the US east coast examined histologically since the mid-1980s. The discovery underscores critical questions about how to assess the risks associated with parasites in groups known to be lethal, but that themselves are not considered a problem.

Associations between land use and Perkinsus marinus infection of eastern oysters in a high salinity, partially urbanized estuary.

Infection levels of eastern oysters by the unicellular pathogen Perkinsus marinus have been associated with anthropogenic influences in laboratory studies. However, these relationships have been difficult to investigate in the field because anthropogenic inputs are often associated with natural influences such as freshwater inflow, which can also affect infection levels. We addressed P. marinus-land use associations using field-collected data from Murrells Inlet, South Carolina, USA, a developed, coastal estuary with relatively minor freshwater inputs. Ten oysters from each of 30 reefs were sampled quarterly in each of 2 years. Distances to nearest urbanized land class and to nearest stormwater outfall were measured via both tidal creeks and an elaboration of Euclidean distance. As the forms of any associations between oyster infection and distance to urbanization were unknown a priori, we used data from the first and second years of the study as exploratory and confirmatory datasets, respectively. With one exception, quarterly land use associations identified using the exploratory dataset were not confirmed using the confirmatory dataset. The exception was an association between the prevalence of moderate to high infection levels in winter and decreasing distance to nearest urban land use. Given that the study design appeared adequate to detect effects inferred from the exploratory dataset, these results suggest that effects of land use gradients were largely insubstantial or were ephemeral with duration less than 3 months.

Shewanella and Photobacterium spp. in oysters and seawater from the Delaware Bay.

Shewanella algae, S. putrefaciens, and Photobacterium damselae subsp. damselae are indigenous marine bacteria and human pathogens causing cellulitis, necrotizing fasciitis, abscesses, septicemia, and death. Infections are rare and are most often associated with the immunocompromised host. A study was performed on the microbiological flora of oysters and seawater from commercial oyster harvesting sites in the Delaware Bay, New Jersey. From 276 water and shellfish samples tested, 1,421 bacterial isolates were picked for biochemical identification and 170 (12.0%) of the isolates were presumptively identified as S. putrefaciens, 26 (1.8%) were presumptively identified as P. damselae subsp. damselae, and 665 (46.8%) could not be identified using the API 20E identification database. Sequencing of the 16S rRNA genes of 22 S. putrefaciens-like isolates identified them as S. abalonesis, S. algae, S. baltica, S. hafniensis, S. marisflavi, S. putrefaciens, Listonella anguillarum, and P. damselae. Beta-hemolysis was produced by some S. algae and P. damselae isolates, while isolates of S. baltica and L. anguillarum, species perceived as nonpathogenic, also exhibited beta-hemolysis and growth at 37 degrees C. To our knowledge, this is the first time these beta-hemolytic strains were reported from shellfish or seawater from the Delaware Bay. Pathogenic Shewanella and Photobacterium species could pose a health threat through the ingestion of contaminated seafood, by cuts or abrasions acquired in the marine environment, or by swimming and other recreational activities.

Perkinsus chesapeaki in stout razor clams Tagelus plebeius from Delaware Bay.

Perkinsus chesapeaki is reported from stout razor clams Tagelus plebeius in Delaware Bay, extending the known range of P. chesapeaki north of Chesapeake Bay. P. marinus, which causes dermo disease, is prevalent in cultured and wild oysters at this site, but was not detected in T. plebeius. Evidence for the presence of disseminated neoplasia, also reported from Chesapeake Bay, was equivocal. Although P. chesapeaki infections were associated with mortality events, light infection intensities and a general lack of histopathological evidence of disease limit inferences about a causal relationship. A comparison of Ray's fluid thioglycollate medium (RFTM)-based and PCR-based detection assays highlight differences in detection capabilities related to the quantity and type of tissue processed rather than assay sensitivity per se, a point that should be considered when surveying populations for disease prevalence. Investigators are further cautioned to use care when applying and interpreting diagnostic assays when used with novel species.

The effects of several common anthropogenic contaminants on proliferation of the parasitic oyster pathogen Perkinsus marinus.

Estuarine contaminants have varying effects on estuarine inhabitants and host-parasite interactions. Some field collected contaminant mixtures have been shown to increase oyster susceptibility to parasitism by Perkinsus marinus, but little is known about contaminant effects on the parasite itself. This study examined the effects of ammonium, nitrate, phosphate, fluoranthene, phenanthrene and a common herbicide mixture (Weed-B-Gone) on in vitro proliferation of P. marinus. Only the herbicide had a significant effect, but not at or below the manufacture's recommended application rate (7.81 microl ml(-1)). The herbicide's active ingredients (3.1% 2,4-dichlorophenoxyacetic acid, 10.6% mecoprop and 1.3% dicamba) mimic growth hormones of broadleaf plants; over stimulation of growth results in death. The mode of action of these compounds on P. marinus warrants further investigation which may provide insight towards the identification of biocides to control P. marinus.

Managing marine mollusc diseases in the context of regional and international commerce: policy issues and emerging concerns.

Marine mollusc production contributes to food and economic security worldwide and provides valuable ecological services, yet diseases threaten these industries and wild populations. Although the infrastructure for mollusc aquaculture health management is well characterized, its foundations are not without flaws. Use of notifiable pathogen lists can leave blind spots with regard to detection of unlisted and emerging pathogens. Increased reliance on molecular tools has come without similar attention to diagnostic validation, raising questions about assay performance, and has been accompanied by a reduced emphasis on microscopic diagnostic expertise that could weaken pathogen detection capabilities. Persistent questions concerning pathogen biology and ecology promote regulatory paralysis that impedes trade and which could weaken biosecurity by driving commerce to surreptitious channels. Solutions that might be pursued to improve shellfish aquaculture health management include the establishment of more broad-based surveillance programmes, wider training and use of general methods like histopathology to ensure alertness to emerging diseases, an increased focus on assay assessment and validation as fundamental to assay development, investment in basic research, and application of risk analyses to improve regulation. A continual sharpening of diagnostic tools and approaches and deepening of scientific knowledge is necessary to manage diseases and promote sustainable molluscan shellfish industries.

Comparison of in vitro-cultured and wild-type Perkinsus marinus. I. Pathogen virulence.

Perkinsus marinus is a highly contagious pathogen of the eastern oyster Crassostrea virginica. Until recently, transmission studies have employed wild-type parasites isolated directly from infected oysters. Newly developed methods to propagate P. marinus in vitro have led to using cultured parasites for infection studies, but results suggest that cultured parasites are less virulent than wild-type parasites In this paper, we report results of experiments designed to quantify differences between wild-type and cultured P. marinus virulence and to test the following hypotheses: (1) in vitro-cultured parasites are less virulent than wild-type parasites; (2) virulence decreases gradually during in vitro culture; (3) virulence of in vitro cultures can be restored by in vivo passage; (4) virulence changes with culture phase. Our results demonstrate that parasites freshly isolated from infected hosts are much more virulent than those propagated in culture, indicating a potential deficiency in the culture medium used. Virulence was lost immediately in culture and, for that reason, the practice of repassing cultured cells through the host to restore virulence does not work for P. marinus. Virulence was also associated with culture phase: log-phase parasites were significantly more virulent than those obtained from lag- or stationary-phase cultures.

Comparison of in vitro-cultured and wild-type Perkinsus marinus. II. Dosing methods and host response.

Endoparasites must breach host barriers to establish infection and then must survive host internal defenses to cause disease. Such barriers may frustrate attempts to experimentally transmit parasites by 'natural' methods. In addition, the host's condition may affect a study's outcome. The experiments reported here examined the effect of dosing method and host metabolic condition on measures of virulence for the oyster parasite Perkinsus marinus. Oysters, Crassostrea virginica, were challenged with wild-type and cultured forms of P. marinus via feeding, shell-cavity injection, gut intubation and adductor-muscle injection. For both parasite types, adductor-muscle injections produced the heaviest infections followed by shell-cavity injection, gut intubation, and feeding. There was no difference in parasite burdens between oysters fed cultured cells by acute vs chronic dosing, and parasite loads stabilized over time, suggesting a dynamic equilibrium between invasion and elimination. P. marinus distribution among tissues of challenged oysters indicated that parasites invaded the mantle and gill, as well as the gut, which has been considered the primary portal of entry. Frequency distributions of P. marinus in oysters challenged with 3 different culture phases indicated an aggregated distribution among hosts and suggested that stationary-phase parasites were easiest for the oyster to control or eliminate and log-phase parasites were the most difficult. Host metabolic condition also affected experimental outcomes, as indicated by increased infection levels in oysters undergoing spawning and/or exposed to low oxygen stress.

Comparison of in vitro-cultured and wild-type Perkinsus marinus. III. Fecal elimination and its role in transmission.

Perkinsus marinus, a pathogen of the eastern oyster Crassostrea virginica, is transmitted directly among oysters. Previous studies found viable P. marinus parasites in the feces and pseudofeces of oysters within hours of injection with parasites, suggesting that the parasite may be voided from live oysters and subsequently dispersed in the water column. The experiments described here were designed to quantify P. marinus shed in the feces and pseudofeces of experimentally infected oysters. The results indicated that parasites were shed in 2 phases. A 'decreasing' phase occurred within 2 wk of challenge and before net parasite proliferation began in the host. An 'increasing' phase occurred after P. marinus had begun replicating. The quantity of P. marinus recovered in the feces and pseudofeces of exposed oysters was only about 5 % of the dose administered. In vitro-cultured P. marinus were eliminated at a greater rate than wild-type P. marinus and the fraction discharged was not associated with culture phase. Oysters that were continuously dosed with P. marinus in their food gradually lost the ability to discard the parasite in pseudofeces. The quantity of P. marinus shed in feces of infected oysters was correlated with both the P. marinus body burden and subsequent survival time, suggesting that noninvasive fecal counts could predict infection intensity and survival. The results indicate that in an epizootic, shedding of P. marinus via feces is relatively small compared to the potential number released by cadavers of heavily infected oysters, but that fecal discharge may be important in transmission before infections become lethal.

Serological affinities of the oyster pathogen Perkinsus marinus (Apicomplexa) with some dinoflagellates (Dinophyceae).

The protozoan oyster pathogen Perkinsus marinus is classified in the phylum Apicomplexa, although molecular-genetic and ultrastructural evidence increasingly concur on its closer phylogenetic relationship with the dinoflagellates. To test for evidence of serological epitopes common to P. marinus and dinoflagellates, we probed 19 free-living and 8 parasitic dinoflagellate, or dinoflagellate-like, species for cross-reactivity with polyclonal antibodies to P. marinus. Three of 19 free-living dinoflagellates (16%), and 7 of 8 parasitic dinoflagellates (88%) were labeled by anti-P. marinus antibodies. In reciprocal immunoassays using polyclonal antibodies to the Hematodinium sp. dinoflagellate parasite of Norway lobsters, Nephrops norvegicus, P. marinus and the same 7 parasitic dinoflagellates labeled by anti-P. marinus antibodies, were again labeled. The dinoflagellate-like parasite of prawns Pandalus platyceros was not labeled by either antibody reagent. These reciprocal results confirm the presence of shared antibody-binding epitopes on cells of P. marinus and several dinoflagellates. The apparent widespread serological affinity between P. marinus and the parasitic dinoflagellates suggests a closer phylogenetic link to the syndinean dinoflagellate lineage. The consistent failure of the dinoflagellate-like prawn parasite to bind either antibody reagent shows that this parasite is serologically distinct from both P. marinus and Hematodinium-species parasitic dinoflagellates.