Morphological variability and genetic analysis of Thalassiosira tenera (Bacillariophyta), a dominant phytoplankton species from the northwestern Sea of Japan

ABSTRACT

Thalassiosira species significantly contribute to phytoplankton communities, forming algal blooms in temperate and polar regions, and are broadly used as model organisms for nanotechnology and as important food sources in the aquaculture industry. Despite being widespread in the world’s oceans, data on abundance and seasonal patterns of individual species of Thalassiosira are sparse. In the present study, we have identified Thalassiosira tenera from the northwestern Sea of Japan, using light and scanning electron microscopy (SEM), and molecular genetic analysis of 28S rDNA sequence. Based on field and cultured material, morphological variability of T. tenera was studied; a detailed diagnostic description of the species is provided, and its morphometry is compared with that of the morphologically similar T. exigua. Growth peculiarities of the species were investigated in laboratory culture; variations in frustule morphology occur at different growth stages. The degree of frustule silicification is assumed to depend on the stage of cell development. By SEM observations of field samples, the seasonal dynamics of the species was examined and data on its abundance are provided for the first time. Findings indicate that T. tenera is present year-round in the phytoplankton assemblage in the northwestern Sea of Japan. The species dominates the community from November to February, accounting for more than 60% of the total phytoplankton abundance. The highest numbers, 7,281 cells l⁻¹, were recorded under the sea ice in January, and the lowest numbers, less than 100 cells l⁻¹, occurred in April. In addition, the study gives information on the species ecology.

KEYWORDS:

• Diatoms
• Dynamics
• LSU rDNA
• Morphology
• Sea of Japan

ACKNOWLEDGEMENTS

The research was conducted at the Primorsky Aquarium Shared Equipment Facility, NSCMB FEB RAS (Vladivostok, Russia). Electron microscopical investigations were carried out at the Far Eastern Center of Electron Microscopy, NSCMB FEB RAS. The authors are sincerely grateful to the staff of the Center for their assistance with electron microscopy.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the authors.

SUPPLEMENTARY MATERIAL

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Additional information

Funding

This work was supported by the Russian Foundation for Basic Research grant # 19-04-00752.