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Advances in the aquatic sciences
RESEARCH ARTICLE

The Black Sea autumn bloom of the diatom Hemiaulus hauckii Grunow ex Van Heurck: peculiarities of the phytoplankton’s structural and functional parameters

L. V. Stelmakh https://orcid.org/0000-0003-2970-0281 A * , A. A. Farber A , I. V. Kovaleva A and D. S. Borisova A
+ Author Affiliations
- Author Affiliations

A A.O. Kovalevsky Institute of Biology of the Southern Seas of RAS, 2 Nakhimov Avenue, Sevastopol 299011, Russian Federation.

* Correspondence to: lustelm@mail.ru

Handling Editor: Yunlin Zhang

Marine and Freshwater Research 76, MF25109 https://doi.org/10.1071/MF25109
Submitted: 14 May 2025  Accepted: 28 September 2025  Published: 13 October 2025

© 2025 The Author(s) (or their employer(s)). Published by CSIRO Publishing

Abstract

Context

The fixation of atmospheric nitrogen in the sea is an important source of new nitrogen to the ocean surface waters, stimulating phytoplankton productivity. Diazotrophic cyanobacterium R. intracellularis in association with the large diatom Hemiaulus hauckii Grunow ex Van Heurck is often responsible for nitrogen fixation.

Aims

To examine the peculiarities of the phytoplankton structural and functional traits during the autumn diatom–diazotroph association (DDA) Hemiaulus–Richellii bloom in the Black Sea.

Methods

A cruise was conducted aboard the Research Vessel ‘Professor Vodyanitsky’ in October 2022. The process involved the use of light microscopy, hydrochemical and hydrobiological methods, and model calculations.

Key results

In the Black Sea, we recorded the diatom–diazotrophic association Hemiaulus–Richellii bloom for the first time.

Conclusion

The DDA probably triggered the unusually high values of primary production in the autumn period.

Implication

The obtained results are important for the development of a modern model of the functioning of the Black Sea ecosystem.

Keywords: Black Sea, chlorophyll-a, diatom bloom, Hemiaulus hauckii, nutrients, phytoplankton biomass, primary production, Richelia intracellularis.

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