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.
Competing Interests: Declaration of Competing Interest The authors of the manuscript Tatiana V. Orlova, Anatoly L Aleksanin., Ekaterina V. Lepskaya, Kseniya V. Efimova, Marina S. Selina, Tatiana V. Morosova, Inna V. Stonik, Vasily A. Kachur, Alexander A. Karpenko, Kirill A. Vinnikov, Andrey V. Adrianov, Mitsunori Iwataki "A massive bloom of Karenia species (Dinophyceae) off the Kamchatka coast, Russia, in the fail of 2020" declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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