Natural transmission of Hematodinium perezi in juvenile blue crabs (Callinectes sapidus) in the laboratory.

Hematodinium perezi is a dinoflagellate endoparasitic in marine crustaceans, primarily decapods. It occurs in juvenile blue crabs, Callinectes sapidus, at high prevalence levels and has severe pathogenic effects in this host. The life history outside the host has not been experimentally investigated and, until now, transmission using dinospores has not been successful. We investigated the natural transmission dynamics of H. perezi in the laboratory using small juvenile crabs, which are highly susceptible to infection in the field, and elevated temperatures, which are known to stimulate dinospore production. Natural water-borne transmission to naïve crabs varied between 7 and 100% and was not correlated with dinospore densities measured from their aquaria water. Infections appeared to develop quickly in naïve hosts at 25 °C, suggesting that elevated temperatures as seen in the late summer and early autumn have a strong influence on the transmission of H. perezi in natural systems.

A Deterministic Model for Understanding Nonlinear Viral Dynamics in Oysters.

Contamination of oysters with a variety of viruses is one key pathway to trigger outbreaks of massive oyster mortality as well as human illnesses, including gastroenteritis and hepatitis. Much effort has gone into examining the fate of viruses in contaminated oysters, yet the current state of knowledge of nonlinear virus-oyster interactions is not comprehensive because most studies have focused on a limited number of processes under a narrow range of experimental conditions. A framework is needed for describing the complex nonlinear virus-oyster interactions. Here, we introduce a mathematical model that includes key processes for viral dynamics in oysters, such as oyster filtration, viral replication, the antiviral immune response, apoptosis, autophagy, and selective accumulation. We evaluate the model performance for two groups of viruses, those that replicate in oysters (e.g., ostreid herpesvirus) and those that do not (e.g., norovirus), and show that this model simulates well the viral dynamics in oysters for both groups. The model analytically explains experimental findings and predicts how changes in different physiological processes and environmental conditions nonlinearly affect in-host viral dynamics, for example, that oysters at higher temperatures may be more resistant to infection by ostreid herpesvirus. It also provides new insight into food treatment for controlling outbreaks, for example, that depuration for reducing norovirus levels is more effective in environments where oyster filtration rates are higher. This study provides the foundation of a modeling framework to guide future experiments and numerical modeling for better prediction and management of outbreaks. IMPORTANCE The fate of viruses in contaminated oysters has received a significant amount of attention in the fields of oyster aquaculture, food quality control, and public health. However, intensive studies through laboratory experiments and in situ observations are often conducted under a narrow range of experimental conditions and for a specific purpose in their respective fields. Given the complex interactions of various processes and nonlinear viral responses to changes in physiological and environmental conditions, a theoretical framework fully describing the viral dynamics in oysters is warranted to guide future studies from a top-down design. Here, we developed a process-based, in-host modeling framework that builds a bridge for better communications between different disciplines studying virus-oyster interactions.

Impact of parasitism on levels of human-pathogenic Vibrio species in eastern oysters.

AIMS: To investigate the relationships between individual health status of oysters, particularly with regard to parasitic infection, and variability in abundance of human-pathogenic Vibrio species. METHODS AND RESULTS: Aquacultured eastern oysters, Crassostrea virginica, were analysed individually for infection by the protozoan parasite Perkinsus marinus through quantitative PCR, and total Vibrio vulnificus and total and pathogenic Vibrio parahaemolyticus abundance was assessed using a most probable number (MPN)-qPCR approach. Additionally, perspective on general oyster health and other parasitic infections was obtained through histopathology. Perkinsus marinus infection and human-pathogenic Vibrio species levels were not correlated, but through histology, analyses revealed that oysters infected by Haplosporidium nelsoni harboured more V. vulnificus. CONCLUSIONS: The highly prevalent parasite P. marinus had little influence on human-pathogenic Vibrio species levels in eastern oysters, but the less prevalent parasite, H. nelsoni, may influence V. vulnificus levels, highlighting the potential nuances of within-oyster dynamics of Vibrio species. SIGNIFICANCE AND IMPACT OF THE STUDY: Human-pathogenic bacteria continue to be a concern to the oyster industry and causes for individual oyster variation in bacterial levels remain unknown. The major oyster pathogen P. marinus does not appear to affect levels of these bacteria within oysters, suggesting that other factors may influence Vibrio spp. levels in oysters.

Alkali Metal- and Acid-Catalyzed Interconversion of Goniodomin A with Congeners B and C.

Goniodomin A (GDA, 1) is a phycotoxin produced by at least four species of Alexandrium dinoflagellates that are found globally in brackish estuaries and lagoons. It is a linear polyketide with six oxygen heterocyclic rings that is cyclized into a macrocyclic structure via lactone formation. Two of the oxygen heterocycles in 1 comprise a spiro-bis-pyran, whereas goniodomin B (GDB) contains a 2,7-dioxabicyclo[3.3.1]nonane ring system fused to a pyran. When H2O is present, 1 undergoes facile conversion to isomer GDB and to an α,ß-unsaturated ketone, goniodomin C (GDC, 7). GDB and GDC can be formed from GDA by cleavage of the spiro-bis-pyran ring system. GDA, but not GDB or GDC, forms a crown ether-type complex with K+. Equilibration of GDA with GDB and GDC is observed in the presence of H+ and of Na+, but the equilibrated mixtures revert to GDA upon addition of K+. Structural differences have been found between the K+ and Na+ complexes. The association of GDA with K+ is strong, while that with Na+ is weak. The K+ complex has a compact, well-defined structure, whereas Na+ complexes are an ill-defined mixture of species. Analyses of in vitro A. monilatum and A. hiranoi cultures indicate that only GDA is present in the cells; GDB and GDC appear to be postharvest transformation products.

Algal Toxin Goniodomin A Binds Potassium Ion Selectively to Yield a Conformationally Altered Complex with Potential Biological Consequences.

The marine toxin goniodomin A (GDA) is a polycyclic macrolide containing a spiroacetal and three cyclic ethers as part of the macrocycle backbone. GDA is produced by three species of the Alexandrium genus of dinoflagellates, blooms of which are associated with "red tides", which are widely dispersed and can cause significant harm to marine life. The toxicity of GDA has been attributed to stabilization of the filamentous form of the actin group of structural proteins, but the structural basis for its binding is not known. Japanese workers, capitalizing on the assumed rigidity of the heavily substituted macrolide ring, assigned the relative configuration and conformation by relying on NMR coupling constants and NOEs; the absolute configuration was assigned by degradation to a fragment that was compared with synthetic material. We have confirmed the absolute structure and broad features of the conformation by X-ray crystallography but have found GDA to complex with alkali metal ions in spite of two of the heterocyclic rings facing outward. Such an arrangement would have been expected to impair the ability of GDA to form a crown-ether-type multidentate complex. GDA shows preference for K+, Rb+, and Cs+ over Li+ and Na+ in determinations of relative affinities by TLC on metal-ion-impregnated silica gel plates and by electrospray mass spectrometry. NMR studies employing the K+ complex of GDA, formed from potassium tetrakis[pentafluorophenyl]borate (KBArF20), reveal a major alteration of the conformation of the macrolide ring. These observations argue against the prior assumption of rigidity of the ring. Alterations in chemical shifts, coupling constants, and NOEs indicate the involvement of most of the molecule other than ring F. Molecular mechanics simulations suggest K+ forms a heptacoordinate complex involving OA, OB, OC, OD, OE, and the C-26 and C-27 hydroxy groups. We speculate that complexation of K+ with GDA electrostatically stabilizes the complex of GDA with filamentous actin in marine animals due to the protein being negatively charged at physiological pH. GDA may also cause potassium leakage through cell membranes. This study provides insight into the structural features and chemistry of GDA that may be responsible for significant ecological damage associated with the GDA-producing algal blooms.

First comparison of French and Australian OsHV-1 µvars by bath exposure.

Economically devastating mortality events of farmed and wild shellfish due to infectious disease have been reported globally. Currently, one of the most significant disease threats to Pacific oyster Crassostrea gigas culture is the ostreid herpesvirus 1 (OsHV-1), in particular the emerging OsHV-1 microvariant genotypes. OsHV-1 microvariants (OsHV-1 µvars) are spreading globally, and concern is high among growers in areas unaffected by OsHV-1. No study to date has compared the relative virulence among variants. We provide the first challenge study comparing survival of naïve juvenile Pacific oysters exposed to OsHV-1 µvars from Australia (AUS µvar) and France (FRA µvar). Oysters challenged with OsHV-1 µvars had low survival (2.5% exposed to AUS µvar and 10% to FRA µvar), and high viral copy number as compared to control oysters (100% survival and no virus detected). As our study was conducted in a quarantine facility located ~320 km from the ocean, we also compared the virulence of OsHV-1 µvars using artificial seawater made from either facility tap water (3782 µmol kg-1 seawater total alkalinity) or purchased distilled water (2003 µmol kg-1). Although no differences in survival or viral copy number were detected in oysters exposed to seawater made using tap or distilled water, more OsHV-1 was detected in tanks containing the lower-alkalinity seawater, indicating that water quality may be important for virus transmission, as it may influence the duration of viral viability outside of the host.

A novel monoclonal Perkinsus chesapeaki in vitro isolate from an Australian cockle, Anadara trapezia.

A monoclonal Perkinsus chesapeaki isolate was established from 1 of 10 infected Australian Anadara trapezia cockles. Morphological features were similar to those of described P. chesapeaki isolates, and also included a unique vermiform schizont cell-type. Perkinsus olseni-specific PCR primers amplified DNAs from all 10 cockles. Perkinsus chesapeaki-specific primers also amplified DNAs from 4/10 cockles, including DNA from the isolate source cockle. Three different sets of DNA sequences from the monoclonal isolate grouped with the homologous, previously deposited, P. chesapeaki sequences in phylogenetic analyses. In situ hybridization assays detected both P. chesapeaki and P. olseni cells in histological sections from the source cockle for monoclonal isolate ATCC PRA-425.

First report of Perkinsus honshuensis in the variegated carpet shell clam Ruditapes variegatus in Korea.

The recent discovery of Perkinsus honshuensis, a new Perkinsus species infecting Manila clams Ruditapes philippinarum (Sowerby, 1852), in Japan, suggested that, based on proximity, P. honshuensis could also be in Korean waters, where to date, P. olseni was believed to be the only Perkinsus species present. Perkinsus sp. infections consistently occurred among Ruditapes variegatus clams on a pebble beach on Jeju Island, off the south coast of Korea. The typical 'signet ring' morphology of the parasite was observed in the connective tissue of the digestive gland, and infection intensity was comparatively low (3.3 × 103 ± 1.2 × 104 to 1.3 × 104 ± 6.1 × 104 cells g-1 gill weight). Further DNA analyses of internal transcribed spacer (ITS-1, 5.8S and ITS-2) and non-transcribed spacer (NTS) regions of the parasite showed 98.9-99.8 and 98.5-99.5% similarity to those of P. honshuensis from Japan, respectively. Phylogenetic analyses using ITS and NTS sequences indicated that Perkinsus sp. from Jeju formed a highly supported clade with P. honshuensis. This is the first report of P. honshuensis infections in clams in Korean waters and the first report of R. variegatus as a host for that parasite.

Update of information on perkinsosis in NW Mediterranean coast: Identification of Perkinsus spp. (Protista) in new locations and hosts.

This study addressed perkinsosis in commercially important mollusc species in the western Mediterranean area. Perkinsus olseni was found in Santa Gilla Lagoon (Sardinia) infecting Ruditapes decussatus, Cerastoderma glaucum and Venerupis aurea, in Balearic Islands infecting Venus verrucosa and in Delta de l'Ebre (NE Spain) parasitising Ruditapes philippinarum and R. decussatus. Perkinsus mediterraneus was detected infecting Ostrea edulis from the Gulf of Manfredonia (SE Italy) and Alacant (E Spain), V. verrucosa and Arca noae from Balearic Islands and Chlamys varia from Balearic Islands, Alacant and Delta de l'Ebre.

Perkinsus sp. infections and in vitro isolates from Anadara trapezia (mud arks) of Queensland, Australia.

Perkinsus sp. protists were found infecting Anadara trapezia mud ark cockles at 6 sites in Moreton Bay, Queensland, Australia, at prevalences of 4 to 100% during 2011 as determined by surveys using Ray's fluid thioglycollate medium. Perkinsus sp. lesions were found among gill and visceral connective tissues in histological samples from several cockles, where basophilic, eccentrically vacuolated Perkinsus sp. signet ring trophozoites and proliferating, Perkinsus sp. schizont cells were documented. Two Perkinsus sp. isolates were propagated in vitro during August 2013 from gill tissues of a single infected A. trapezia cockle from Wynnum in Moreton Bay. DNA from those isolate cells amplified universally by a Perkinsus genus-specific PCR assay, and rDNA-internal transcribed spacer sequences respectively grouped them with P. olseni and P. chesapeaki in phylogenetic analyses. This is the first report of P. chesapeaki in Australia, and the first report of a P. chesapeaki in vitro isolate from an Australian mollusc host. Although P. olseni was originally described in 1981 as a pathogen of abalone in South Australia, and has subsequently been identified as a prevalent pathogen of numerous other molluscs worldwide, this is also the first report of a P. olseni-like in vitro isolate from an Australian mollusc host.

Two Perkinsus spp. infect Crassostrea gasar oysters from cultured and wild populations of the Rio São Francisco estuary, Sergipe, northeastern Brazil.

Brazilian production of bivalve molluscs is small but expanding, especially in the northeastern region where the native oysters Crassostrea rhizophorae and C. gasar are abundant, and tropical weather promotes their rapid growth. Studies on bivalve pathology are scarce in Brazil, with only a few employing techniques for detecting protozoan pathogens listed by the World Organisation for Animal Health (OIE). In 2008, a Perkinsus sp. was reported for the first time in Brazil, infecting C. rhizophorae oysters from a wild population in Ceará state, NE Brazil. Recently P. marinus was detected in the same oyster species in nearby Paraíba state. These findings highlighted the need to expand knowledge on the presence and impacts of Perkinsus spp. on Brazilian oyster populations. The current investigation evaluated Perkinsus sp. infections among wild and cultured C. gasar mangrove oysters from the estuary of the Rio São Francisco, Sergipe state, NE Brazil. Our results show that Perkinsus sp. infections occurred commonly in oysters of both groups, at prevalences that were frequently higher among cultured oysters. Prevalences varied seasonally, with maximum values during summer (January) of 57% and 80% for wild and cultured oysters respectively, and minimum values during winter (July). Results of DNA sequencing, in situ hybridization assays, and phylogenetic analyses showed dual- and single-pathogen infections by P. marinus and/or P. olseni in the tested oysters.

Phylogenetics of Bonamia parasites based on small subunit and internal transcribed spacer region ribosomal DNA sequence data.

The genus Bonamia (Haplosporidia) includes economically significant oyster parasites. Described species were thought to have fairly circumscribed host and geographic ranges: B. ostreae infecting Ostrea edulis in Europe and North America, B. exitiosa infecting O. chilensis in New Zealand, and B. roughleyi infecting Saccostrea glomerata in Australia. The discovery of B. exitiosa-like parasites in new locations and the observation of a novel species, B. perspora, in non-commercial O. stentina altered this perception and prompted our wider evaluation of the global diversity of Bonamia parasites. Samples of 13 oyster species from 21 locations were screened for Bonamia spp. by PCR, and small subunit and internal transcribed spacer regions of Bonamia sp. ribosomal DNA were sequenced from PCR-positive individuals. Infections were confirmed histologically. Phylogenetic analyses using parsimony and Bayesian methods revealed one species, B. exitiosa, to be widely distributed, infecting 7 oyster species from Australia, New Zealand, Argentina, eastern and western USA, and Tunisia. More limited host and geographic distributions of B. ostreae and B. perspora were confirmed, but nothing genetically identifiable as B. roughleyi was found in Australia or elsewhere. Newly discovered diversity included a Bonamia sp. in Dendostrea sandvicensis from Hawaii, USA, that is basal to the other Bonamia species and a Bonamia sp. in O. edulis from Tomales Bay, California, USA, that is closely related to both B. exitiosa and the previously observed Bonamia sp. from O. chilensis in Chile.

Genetic population structure of US atlantic coastal striped bass (Morone saxatilis).

Genetic population structure of anadromous striped bass along the US Atlantic coast was analyzed using 14 neutral nuclear DNA microsatellites. Young-of-the-year and adult striped bass (n = 1114) were sampled from Hudson River, Delaware River, Chesapeake Bay, North Carolina, and South Carolina. Analyses indicated clear population structure with significant genetic differentiation between all regions. Global multilocus F ST was estimated at 0.028 (P < 0.001). Population structure followed an isolation-by-distance model and temporal sampling indicated a stable population structure more than 2 years at all locations. Significant structure was absent within Hudson River, whereas weak but significant genetic differences were observed between northern and southern samples in Chesapeake Bay. The largest and smallest effective striped bass population sizes were found in Chesapeake Bay and South Carolina, respectively. Coalescence analysis indicated that the highest historical gene flow has been between Chesapeake Bay and Hudson River populations, and that exchange has not been unidirectional. Bayesian analysis of contemporary migration indicated that Chesapeake Bay serves as a major source of migrants for Atlantic coastal regions from Albemarle Sound northward. In addition to examining population genetic structure, the data acquired during this project were capable of serving as a baseline for assigning fish with unknown origin to source region.

Conservation in the first internal transcribed spacer (ITS1) region of Hematodinium perezi (genotype III) from Callinectes sapidus .

Hematodinium spp. infections have been reported from blue crabs Callinectes sapidus in high-salinity waters of the USA from New Jersey to Texas. Recently, H. perezi (genotype III) has been proposed as the parasite species and genotype infecting blue crabs from Virginia; however, it is unknown whether this same genotype is present in blue crabs from other locations. To address this question, we collected 317 blue crabs from Massachusetts, Virginia, Georgia, Florida, Louisiana, and Texas to test for the presence of H. perezi (III) using a specific PCR assay targeting the first internal transcribed spacer (ITS1) region of the ribosomal RNA gene complex. To examine the genetic variation within H. perezi (III), ITS1 region sequences from the parasite in blue crabs from multiple locations were compared to each other and to those of H. perezi (III) found in alternate hosts from Virginia. In total, 34 distinct ITS1 sequence variants of the parasite were identified from blue crabs alone, and 38 distinct variants were identified when alternate hosts were included. However, a single ITS1 sequence variant appeared in all geographic regions and hosts, and also in blue crabs sampled from a previous study. The high similarity among all the ITS1 region sequences examined (>98%) and the observation of a single variant found throughout a large geographic range, strongly suggests that a single species and genotype of Hematodinium, specifically H. perezi (III), infects blue crabs from Virginia to Texas and multiple alternate host species in Virginia.

Fine-scale population structure of the northern hard clam (Mercenaria mercenaria) revealed by genome-wide SNP markers.

Aquaculture is growing rapidly worldwide, and sustainability is dependent on an understanding of current genetic variation and levels of connectivity among populations. Genetic data are essential to mitigate the genetic and ecological impacts of aquaculture on wild populations and guard against unintended human-induced loss of intraspecific diversity in aquacultured lines. Impacts of disregarding genetics can include loss of diversity within and between populations and disruption of local adaptation patterns, which can lead to a decrease in fitness. The northern hard clam, Mercenaria mercenaria (Linnaeus, 1758), is an economically valuable aquaculture species along the North American Atlantic and Gulf coasts. Hard clams have a pelagic larval phase that allows for dispersal, but the level of genetic connectivity among geographic areas is not well understood. To better inform the establishment of site-appropriate aquaculture brood stocks, this study used DArTseq™ genotyping by sequencing to characterize the genetic stock structure of wild clams sampled along the east coast of North America and document genetic diversity within populations. Samples were collected from 15 locations from Prince Edward Island, Canada, to South Carolina, USA. Stringent data filtering resulted in 4960 single nucleotide polymorphisms from 448 individuals. Five genetic breaks separating six genetically distinct populations were identified: Canada, Maine, Massachusetts, Mid-Atlantic, Chesapeake Bay, and the Carolinas (F ST 0.003-0.046; p < 0.0001). This is the first study to assess population genetic structure of this economically important hard clam along a large portion of its native range with high-resolution genomic markers, enabling identification of previously unrecognized population structure. Results of this study not only broaden insight into the factors shaping the current distribution of M. mercenaria but also reveal the genetic population dynamics of a species with a long pelagic larval dispersal period along the North American Atlantic and Gulf coasts.

Mass spectrometric characterization of the seco acid formed by cleavage of the macrolide ring of the algal metabolite goniodomin A.

Goniodomin A (GDA) is a polyketide macrolide produced by multiple species of the marine dinoflagellate genus Alexandrium. GDA is unusual in that it undergoes cleavage of the ester linkage under mild conditions to give mixtures of seco acids (GDA-sa). Ring-opening occurs even in pure water although the rate of cleavage accelerates with increasing pH. The seco acids exist as a dynamic mixture of structural and stereo isomers which is only partially separable by chromatography. Freshly prepared seco acids show only end absorption in the UV spectrum but a gradual bathochromic change occurs, which is consistent with formation of α,ß-unsaturated ketones. Use of NMR and crystallography is precluded for structure elucidation. Nevertheless, structural assignments can be made by mass spectrometric techniques. Retro-Diels-Alder fragmentation has been of value for independently characterizing the head and tail regions of the seco acids. The chemical transformations of GDA revealed in the current studies help clarify observations made on laboratory cultures and in the natural environment. GDA has been found to reside mainly within the algal cells while the seco acids are mainly external with the transformation of GDA to the seco acids occurring largely outside the cells. This relationship, plus the fact that GDA is short-lived in growth medium whereas GDA-sa is long-lived, suggests that the toxicological properties of GDA-sa in its natural environment are more important for the survival of the Alexandrium spp. than those of GDA. The structural similarity of GDA-sa to that of monensin is noted. Monensin has strong antimicrobial properties, attributed to its ability to transport sodium ions across cell membranes. We propose that toxic properties of GDA may primarily be due to the ability of GDA-sa to mediate metal ion transport across cell membranes of predator organisms.

Co-occurrence of marine and freshwater phycotoxins in oysters, and analysis of possible predictors for management.

Oysters (Crassostrea virginica) were screened for 12 phycotoxins over two years in nearshore waters to collect baseline phycotoxin data and to determine prevalence of phycotoxin co-occurrence in the commercially and ecologically-relevant species. Trace to low concentrations of azaspiracid-1 and -2 (AZA1, AZA2), domoic acid (DA), okadaic acid (OA), and dinophysistoxin-1 (DTX1) were detected, orders of magnitude below seafood safety action levels. Microcystins (MCs), MC-RR and MC-YR, were also found in oysters (maximum: 7.12 µg MC-RR/kg shellfish meat wet weight), warranting consideration of developing action levels for freshwater phycotoxins in marine shellfish. Oysters contained phycotoxins that impair shellfish health: karlotoxin1-1 and 1-3 (KmTx1-1, KmTx1-3), goniodomin A (GDA), and pectenotoxin-2 (PTX2). Co-occurrence of phycotoxins in oysters was common (54%, n = 81). AZAs and DA co-occurred most frequently of the phycotoxins investigated that are a concern for human health (n = 13) and PTX2 and KmTxs co-occurred most frequently amongst the phycotoxins of concern for shellfish health (n = 9). Various harmful algal bloom (HAB) monitoring methods and tools were assessed for their effectiveness at indicating levels of phycotoxins in oysters. These included co-deployed solid phase adsorption toxin tracking (SPATT) devices, toxin levels in particulate organic matter (POM, >1.5 µm) and whole water samples and cell concentrations from water samples as determined by microscopy and quantitative real-time PCR (qPCR). The dominant phycotoxin varied between SPATTs and all other phycotoxin sample types, and out of the 11 phycotoxins detected in oysters, only four and seven were detected in POM and whole water respectively, indicating phycotoxin profile mismatch between ecosystem compartments. Nevertheless, there were correlations between DA in oysters and whole water (simple linear regression [LR]: R2 = 0.6, p < 0.0001, n = 40), and PTX2 in oysters and SPATTs (LR: R2 = 0.3, p = 0.001, n = 36), providing additional monitoring tools for these phycotoxins, but oyster samples remain the best overall indicators of seafood safety.

Morphological and molecular characterization of Hematodinium perezi (Dinophyceae: Syndiniales), a dinoflagellate parasite of the harbour crab, Liocarcinus depurator.

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.

Blooms of the harmful algae Margalefidinium polykrikoides and Alexandrium monilatum alter the York River Estuary microbiome.

Harmful algal blooms (HABs) cause damage to fisheries, aquaculture, and human health around the globe. However, the impact of HABs on water column microbiomes and biogeochemistry is poorly understood. This study examined the impacts of consecutive blooms of the ichthyotoxic dinoflagellates Margalefidinium polykrikoides and Alexandrium monilatum on the water microbiome in the York River Estuary, Chesapeake Bay, USA. The samples dominated by single dinoflagellate species and by a mix of the two dinoflagellates had different microbiome compositions than the ones with low levels of both species. The M. polykrikoides bloom was co-dominated by Winogradskyella and had increased concentrations of dissolved organic carbon. The A. monilatum bloom had little impact on the prokaryotic portion of the whole community but was associated with a specific group of prokaryotes in the particle-attached (>3 µm) fraction including Candidatus Nitrosopumilus, Candidatus Actinomarina, SAR11 Clade Ia, Candidatus Bealeia, and Rhodobacteraceae HIMB11. Thus, blooms of these two algal species impacted the estuarine microbiome in different ways, likely leading to shifts in estuarine carbon and nutrient cycling, with M. polykrikoides potentially having a greater impact on carbon cycling in the estuarine ecosystem than A. monilatum.

Vibrio vulnificus and Vibrio parahaemolyticus in Oysters under Low Tidal Range Conditions: Is Seawater Analysis Useful for Risk Assessment?

Human-pathogenic Vibrio bacteria are acquired by oysters through filtering seawater, however, the relationships between levels of these bacteria in measured in oysters and overlying waters are inconsistent across regions. The reasons for these discrepancies are unclear hindering our ability to assess if -or when- seawater samples can be used as a proxy for oysters to assess risk. We investigated whether concentrations of total and human pathogenic Vibrio vulnificus (vvhA and pilF genes) and Vibrio parahaemolyticus (tlh, tdh and trh genes) measured in seawater reflect concentrations of these bacteria in oysters (Crassostrea virginica) cultured within the US lower Chesapeake Bay region. We measured Vibrio spp. concentrations using an MPN-qPCR approach and analyzed the data using structural equation modeling (SEM). We found seawater concentrations of these bacteria to predictably respond to temperature and salinity over chlorophyll a, pheophytin or turbidity. We also inferred from the SEM results that Vibrio concentrations in seawater strongly predict their respective concentrations in oysters. We hypothesize that such seawater-oyster coupling can be observed in regions of low tidal range. Due to the ease of sampling and processing of seawater samples compared to oyster samples, we suggest that under low tidal range conditions, seawater samples can foster increased spatial and temporal coverage and complement data associated with oyster samples.