Can functional units of protozoan periphytons be used to evaluate ecological quality status under harmful algal blooms in marine ecosystems?

Based on biological traits the ecological quality status (EQS) under the pressure of two harmful algal bloom (HAB) species was evaluated using functional units (FUs) of protozoan periphytons. Five treatments with different concentrations of Alexandrium tamarense and Gymnodinium catenatum were designed as100, 102, 103, 104 and 105 cell ml− 1. A total of 21 FUs were identified from 25 test protozoan species. Vagile algivores with large sizes showed a decreasing trend towards high concentrations, while the vagile bacterivores and non-selectives with small sizes were dominating in concentrations (104 cell ml− 1) of both algal species. Ellipse test on pair-wise functional distinctness indices revealed a significant departure of test protozoan samples from an expected pattern when algal concentrations were over 104 cell ml− 1. Thus, it is suggested that FUs of protozoan periphyton assemblages may be used as a useful tool for evaluating the effects of HAB on ecological quality status in marine ecosystems.

The Influence of the Toxin-Producing Dinoflagellate, Alexandrium catenella (1119/27), on the Survival and Reproduction of the Marine Copepod, Acartia tonsa, During Prolonged Exposure

Copepods can feed on, and may regulate, the blooms of harmful algae (HA), and may also facilitate dinoflagellate blooms by inducing toxin production and through selective grazing. However, exposure to HA may also cause mortality and reproductive impairment in copepods, with detrimental effects at the population-scale. Here we present the toxin profile of the dinoflagellate, Alexandrium catenella (formerly Alexandrium tamarense), and examine how it affects the survival and reproduction of the cosmopolitan marine copepod, Acartia tonsa. Healthy adult copepods were exposed to mono-specific diets of toxic and non-toxic strains of A. catenella (1119/27 and 1119/19, respectively) and non-toxic Rhodomonas sp. for 10 days alongside unfed controls to examine how their survival was influenced by likely HA bloom conditions. Additional 2-day experiments examined how their egg production rate and hatching success were affected by food deprivation, toxic A. catenella, a non-toxic alternative and a mixture of toxic and non-toxic prey, at high and low concentrations. Survival of A. tonsa declined over the 10-day experiment in all treatments but was not significantly lower in the toxic A. catenella treatment; mortality was only significantly enhanced in the unfed animals, which showed 100% mortality after 9 days. Egg production rates and hatching success from females in the unfed and toxic A. catenella treatments were all significantly lower than values observed in females fed Rhodomonas sp. or non-toxic A. catenella. Animals offered 1,000 μg C L–1 of Rhodomonas sp. and a 50:50 mixture of toxic A. catenella and Rhodomonas sp. produced significantly more eggs than animals fed toxic A. catenella alone. These results were not apparent at prey concentrations of 100 μg C L–1. The percentages of eggs to successfully hatch from females offered mono-specific diets of toxic A. catenella were always close to zero. Collectively, our results indicate that adult female A. tonsa can acquire sufficient energy from toxic A. catenella to survive, but suffer reproductive impairment when feeding on this prey alone.

Nitratireductor alexandrii sp. nov., from phycosphere microbiota of toxic marine dinoflagellate Alexandrium tamarense

A taxonomic study was carried out on a novel algae-associated bacterial strain Z3-1T, which was isolated from phycosphere microbiota of toxic marine dinoflagellate Alexandrium tamarense 880. Cells of strain Z3-1T were Gram-stain-negative, rod-shaped and strictly aerobic and were motile by means of flagella. Strain Z3-1T grew at 25–42 °C, pH 5.0–10.0 and 1.0–5.0 % (w/v) NaCl. Strain Z3-1T reduced nitrate to nitrite, but did not reduce nitrite to nitrogen gas. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain Z3-1T belongs to the genus Nitratireductor showing the highest sequence similarity (97.0 %) to Nitratireductor basaltis JCM 14935T. The average nucleotide identity and digital DNA–DNA hybridization relatedness between strain Z3-1T and type strains of genus Nitratireductor with available genome sequences were in the ranges of 72.4–74.4 % and 22.7–23.3 %, respectively. The major fatty acids were summed in feature 8 (C18:1 ω7c and/or C18:1 ω6c), C19:0 ω8c cyclo, C18:1 ω7c 11-metyl and iso-C17:0. The major polar lipids were determined as diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, two unidentified phospholipids and four unidentified polar lipids. The genomic DNA G+C content calculated from genome sequence was 65.6 mol%. Based on genotypic, chemotaxonomic and phenotypic data obtained, strain Z3-1T represents a novel species of the genus Nitratireductor , for which the name Nitratireductor alexandrii sp. nov. is proposed with the type strain Z3-1T (=KCTC 62458T=CCTCC AB 2017227T).

Comparing metabarcoding and morphological approaches to identify phytoplankton taxa associated with harmful algal blooms

Molecular techniques are expected to be highly useful in detecting taxa causing harmful algal blooms (HABs). This is the first report in Canada evaluating HABs-related species identification using a combination of morphological and molecular approaches. Microscopy, quantitative polymerase chain reaction (qPCR), and metabarcoding with multiple markers (i.e., 16S, 18S-dinoflagellate and 18S-diatom, large subunit (28S) rDNA) were applied on samples ( n = 54) containing suspected harmful algae (e.g., Alexandrium spp., Chattonella sp., Chrysochromulina spp., Dictyocha spp., Heterosigma akashiwo, Protoceratium reticulatum, Pseudochattonella verruculosa, Pseudo-nitzschia spp., Pseudopedinella sp.). Owing to methodology limitations, qPCR result interpretation was limited, although good detectability occurred using previously published assays for Alexandrium tamarense, H. akashiwo, and P. verruculosa. Overall, the multiple-marker metabarcoding results were superior to the morphology-based methods, with the exception of taxa from the silicoflagellate group. The combined results using both 18S markers and the 28S marker together closely corresponded with morphological identification of targeted species, providing the best overall taxonomic coverage and resolution. The most numerous unique taxa were identified using the 18S-dinoflagellate amplicon, and the best resolution to the species level occurred using the 28S amplicon. Molecular techniques are therefore promising for HABs taxa detection but currently depend on deploying multiple markers for metabarcoding.

Redefinition of the Dinoflagellate Genus Alexandrium Based on Centrodinium: Reinstatement of Gessnerium and Protogonyaulax, and Episemicolon gen. nov. (Gonyaulacales, Dinophyceae)

The genus Centrodinium contains oceanic and predominantly tropical species that have received little attention. Three species of Centrodinium were examined using thecal plate dissociation, scanning electron microscopy, and molecular sequences. The apical horn of Centrodinium intermedium and C. eminens is formed by the elongation of the fourth apical plate, and a second apical split into two plates. In C. punctatum two apical plates (2′ and 4′) almost completely encircle the apical pore plate (Po), while the contact with the plate 1′ in the ventral side is much reduced, and the plate 3′ does not reach the Po. Moreover, its left posterior lateral sulcal plate is longer than its right pair, while reversed in the typical Centrodinium spp. The sulcal posterior plate of C. punctatum is located in the left-ventral side below the plates 1′′′ and 2′′′, while the sulcal posterior plate located in the right face below the plates 4′′′ and 5′′′ in the typical Centrodinium spp. Phylogenetic analyses based on the small and large subunit of the rRNA gene showed that Centrodinium spp. and Alexandrium affine/A. gaarderae clustered as a sister clade of the Alexandrium tamarense/catenella/fraterculus groups. The clade of the subgenus Gessnerium, and the clade of the type species of Alexandrium, A. minutum, with four divergent species, clustered in more basal positions. The polyphyly of Alexandrium is solved with the split into four genera: (1) Alexandrium sensu stricto for the species of the clade of A. minutum and four divergent species; (2) the reinstatement of the genus Gessnerium for the species of the clade of A. monilatum; (3) the reinstatement of genus Protogonyaulax for the species of the tamarense/catenella/fraterculus groups, and (4) the new genus Episemicolon gen. nov. for A. affine and A. gaarderae. New combinations in the genera Gessnerium, Protogonyaulax, and Episemicolon are proposed.

Temporal Variation of the Profile and Concentrations of Paralytic Shellfish Toxins and Tetrodotoxin in the Scallop, Patinopecten yessoensis, Cultured in a Bay of East Japan

Paralytic shellfish toxins (PSTs) are the major neurotoxic contaminants of edible bivalves in Japan. Tetrodotoxin (TTX) was recently detected in bivalve shellfish around the world, drawing widespread attention. In Japan, high levels of TTX were reported in the digestive gland of the scallop, Patinopecten yessoensis, in 1993; however, no new data have emerged since then. In this study, we simultaneously analyzed PSTs and TTX in scallops cultured in a bay of east Japan using hydrophilic interaction chromatography (HILIC)-MS/MS. These scallops were temporally collected from April to December 2017. The highest concentration of PSTs (182 µmol/kg, total congeners) in the hepatopancreas was detected in samples collected on May 23, lined to the cell density of the dinoflagellate, Alexandrium tamarense, in seawater around the scallops, whereas the highest concentration of TTX (421 nmol/kg) was detected in samples collected on August 22. Contrary to the previous report, temporal variation of the PSTs and TTX concentrations did not coincide. The highest concentration of TTX in the entire edible tissues was 7.3 µg/kg (23 nmol/kg) in samples obtained on August 22, which was lower than the European Food Safety Authority (EFSA)-proposed threshold, 44 µg TTX equivalents/kg shellfish meat. In addition, 12β-deoxygonyautoxin 3 was firstly identified in scallops.

Combining metabarcoding and morphological approaches to identify phytoplankton taxa associated with harmful algal blooms

Molecular techniques are expected to be highly useful in detecting taxa causing harmful algal blooms (HABs). This is the first report in Canada evaluating HABs-related species identification using a combination of morphological and molecular approaches. Microscopy, quantitative polymerase chain reaction (qPCR), and metabarcoding with multiple markers (i.e. 16S, 18S-dinoflagellate and 18S-diatom, large subunit (28S) rDNA) were applied on samples (n=54) containing suspected harmful algae (e.g. Alexandrium spp., Chattonella sp., Chrysochromulina spp., Dictyocha spp., Heterosigma akashiwo, Protoceratium reticulatum, Pseudochattonella verruculosa, Pseudo-nitzschia spp., Pseudopedinella sp.). Due to methodology limitations, qPCR result interpretation was limited, although good detectability occurred using previously published assays for Alexandrium tamarense, H. akashiwo, and P. verruculosa. Overall, the multiple-marker metabarcoding results were superior to the morphology-based methods, with the exception of taxa from the silicoflagellate group. The combined results using both 18S markers and the 28S marker together closely corresponded with morphological identification of targeted species, providing the best overall taxonomic coverage and resolution. The most numerous unique taxa were identified using the 18S-dinoflagellate amplicon, and the best resolution to the species level occurred using the 28S amplicon. Molecular techniques are therefore highly useful for HABs taxa detection, but currently depend on deploying multiple markers for metabarcoding.

Toxinas paralizantes de moluscos en el Mar Argentino: impacto, transferencia trófica y perspectiva

En el Mar Argentino, los dinoflagelados Gymodinium catenatum y el complejo Alexandrium tamarense/catenella producen potentes neurotoxinas (saxitoxinas) que pueden acumularse en moluscos y producir severas intoxicaciones en humanos conocidas como Intoxicación Paralizante por Moluscos. La transferencia de dichas toxinas a través de la cadena alimentaria puede tener consecuencias graves para la salud humana, la acuicultura, la pesca, la industria y la economía regional. Debido a las implicancias para la salud pública, se ha estudiado en profundidad el rol de los moluscos bivalvos en su transferencia. Sin embargo, es escasa la información que se posee sobre las toxinas bioacumuladas en el resto de los organismos marinos ya que no están sujetos a monitoreo. En un contexto de cambio climático global que puede favorecer la ocurrencia de eventos que involucren a las Toxinas Paralizantes de Moluscos (TPM), se presenta una síntesis de la información actualizada para el Mar Argentino sobre los dinoflagelados que las producen y su distribución, las toxinas involucradas y las transformaciones metabólicas que ocurren en su transferencia dentro de la red trófica. Se explora el impacto de las TPM en la integridad del ecosistema y las medidas de manejo y control que se utilizan para minimizar las consecuencias en la salud pública.