A massive bloom of Karenia species (Dinophyceae) off the Kamchatka coast, Russia, in the fall of 2020.

In the fall of 2020, a long-lasting and massive harmful algal bloom (HAB) with extensive fields of yellow sea foam was observed in relatively cold waters (7-13 °C) off the coasts of the Kamchatka Peninsula, Russia. According to the estimates based on bio-optical parameters in satellite imagery, the Kamchatka bloom 2020 lasted for two months and covered a vast area of more than 300 × 100 km. An abundance of dead fish and invertebrates, including sea urchins, sea anemones, chitons, cephalopods, bivalves were found on shore during the bloom. Animals suffered almost 100% mortality within a depth range between 5 and 20 m. To identify the causative microalgal species, light and scanning electron microscopy, Raman spectroscopy, and molecular phylogenetic approaches were used. The HAB area was estimated by the spectral analysis of satellite-derived imagery. The causative organisms were unarmored dinoflagellates of Karenia species. Their density and biomass reached 100-620 cells·mL-1 and 1300-7700 mg·m-3, respectively, which accounted for 31-99% of the total cell density and 82-99% of the total phytoplankton biomass in late September to mid-October. The dominant species was Karenia selliformis, and the other co-occurring kareniacean species were K. cf. cristata, K. mikimotoi, K. papilionacea, K. longicanalis, and two unidentified morphotypes of Karenia spp. The molecular phylogeny inferred from LSU rDNA and ITS region showed that K. selliformis from Kamchatka in 2020 belonged to the cold-water group I and was identical to K. selliformis strains from Hokkaido, Japan, identified in 2021. This is the first HAB event caused by K. selliformis recorded from Russian coastal waters.

First next-generation sequencing data for Haploporidae (Digenea: Haploporata): characterization of complete mitochondrial genome and ribosomal operon for Parasaccocoelium mugili Zhukov, 1971.

The first data on a whole mitochondrial genome of Haploporidae, Parasaccocoelium mugili (Digenea: Haploporata: Haploporidae) was generated using the next-generation sequencing (NGS) approach. We sequenced the complete mitochondrial DNA (mtDNA) and ribosomal operon of Parasaccocoelium mugili, intestine parasite of mullet fish. The mtDNA of P. mugili contained 14,021 bp, including 12 protein-coding genes, two ribosomal genes, 22 tRNA genes, and non-coding region. The ribosomal operon of P. mugili was 8308 bp in length, including 18S rRNA gene (1981 bp), ITS1 rDNA (955 bp), 5.8S rRNA gene (157 bp), ITS2 rDNA (268 bp), 28S rRNA gene (4180 bp), and ETS (767 bp). We used the mtDNA protein-coding regions to make phylogenetic reconstructions of Haploporidae. Additionally, we performed the sequence cluster analysis based on codon usage bias of most of currently available mitochondrial genome data for trematodes. The observed gene arrangement in mtDNA sequence of P. mugili is identical to those of Plagiorchis maculosus (Rudolphi, 1802). Results of maximum likelihood (ML) phylogenetic analysis showed that P. mugili was closely related to Paragonimus species from the suborder Xiphidiata. The results of sequence cluster analysis based on codon usage bias showed that P. mugili has the highest similarity with Plagiorchis maculosus (Xiphidiata). Our results do not contradict to proposing a new suborder for Haploporoidea-Haploporata. On the basis of obtained results, the relationship between mitochondrial protein-coding gene rearrangements and synonymous nucleotide substitutions in mitochondrial genomes has been suggested.

Revised classification of the righteye flounders (Teleostei: Pleuronectidae) based on multilocus phylogeny with complete taxon sampling.

Members of the family Pleuronectidae are common representatives of the marine benthic fauna inhabiting northern regions of the Atlantic and Pacific oceans. The most recent comprehensive classification of the family, based entirely on morphological synapomorphies, recognized five subfamilies, 23 genera, and 61 extant species. However, several subsequent molecular studies have shown that many synapomorphic characters discovered in the morphological study might represent homoplasies, thereby questioning the reliance on these characters with the warning that they may provide misleading information for testing other morphology-based evolutionary hypotheses. In the present study, we propose a comprehensive taxonomic reassessment of the family Pleuronectidae based on the molecular phylogeny reconstructed from four nuclear and three mitochondrial loci and represented by complete taxon sampling of all but one valid species currently assigned to this family. To check for robustness of the phylogenetic hypothesis, we analyzed the effect of base compositional heterogeneity on phylogenetic signal for each locus and compared six different gene partitioning schemes. The final dataset, comprising 14 partitions and 154 individuals, was used to reconstruct phylogenetic trees in RAxML, MrBayes and BEAST2. Alternative topologies for several questionable nodes were compared using Bayes factors. The topology with the highest marginal likelihood was selected as the final phylogenetic tree for inferring pleuronectid relationships and character evolution. Based on our results, we recognize the Pleuronectidae comprising five subfamilies, 24 genera and 59 species. Our new phylogeny comprises five major monophyletic groups within the family, which we define as the subfamilies within the family: Atheresthinae, Pleuronichthyinae, Microstominae, Hippoglossinae and Pleuronectinae. Taxonomic composition of most of these subfamilies is different from that proposed in previous classifications. We also re-assess hypotheses proposed in earlier studies regarding intra-relationships of species of each lineage. Results of the current study contribute to better understanding of the evolutionary relationships of pleuronectid flatfishes based on molecular evidence, and they also provide the framework towards future comprehensive morphological revision of constituent lineages within the family Pleuronectidae.

Cytochrome oxidase 1 gene sequence analysis in six flatfish species (Teleostei, Pleuronectidae) of Far East Russia with inferences in phylogeny and taxonomy.

Mitochondrial DNA at the cytochrome oxidase 1 (Co-1) gene region was sequenced for six flatfish species (in total, 11 sequences of at least 539 base pairs) from the Far East of Russia and compared with other sequences of Pleuronectiformes, comprising altogether 26 flatfish sequences and two outgroup sequences (Perciformes). An analysis of the protein-coding Co-1 gene revealed a statistically substantiated bias in (T + C):(A + G) content, supporting earlier findings. Average scores of the p-distances for different scales of the evolutionary history at the Co-1 gene revealed a clear pattern of increased nucleotide diversity at four different levels: (1) intraspecies, (2) intragenus, (3) intrafamily, and (4) intra-order. Scores of average p-distances of the four categories of comparison in flatfishes were (1) 0.17 +/- 0.09%, (2) 10.60 +/- 1.57%, (3) 12.40 +/- 0.27%, and (4) 19.93 +/- 0.05%, respectively (mean +/- standard error). These data jointly with current knowledge support the concept that speciation in the order Pleuronectiformes mostly follows a geographic mode through accumulation of numerous small genetic changes over a long period of time. A phylogenetic tree for 26 sequences of flatfishes and two other fishes belonging to ray-finned fishes (Actinopterigii) was developed using the Co-1 gene and four different analytical approaches: neighbour-joining, Bayesian (BA), maximum parsimony (MP), and maximum likelihood. The analysis revealed a monophyletic origin for the representatives of Pleuronectidae, which is the principal flatfish family investigated (73-100% support level in our MP and BA analyses). According to the current and literary data, the monophyletic origin for the six compared flatfish families was well supported. Species identification on a per-individual basis (barcoding tagging) was high.