Effect of water trophic status on bio-optical properties and productive characteristics of phytoplankton of the Black Sea coastal waters near Sevastopol

ABSTRACT

Spectral bio-optical properties and phytoplankton photosynthetic parameters were measured in Black Sea coastal waters near Sevastopol in May–July 2020–2021. Chlorophyll a concentration (Chl-a) differed by more than one order of magnitude between stations (0.20–5.6 mg/m³) due to the effect of the Chyornaya river runoff. Light absorption coefficients by all optically active components as well as total non-water absorption coefficients co-varied with Chl-a, which reflected a link between trophic status and water optical properties. An increase in total non-water absorption resulted in a shift of the maximum of downwelling irradiance to the longer wavelength (from 511 nm to 567 nm). Phytoplankton photosynthetic parameters were depth-dependent variables due to phytoplankton acclimations to light intensity without dependence on water trophic status. Gross primary production was estimated by the full spectral approach. Primary production (1.3–31 mgC/m³/h) co-varied with Chl-a. Chlorophyll a specific photosynthesis rate (4.3–8.0 mgC/mgChl/h) varied by about twice at the sea surface but no dependence on Chl-a was revealed.

KEYWORDS:

• Primary production
• spectral downwelling irradiance
• spectral light absorption coefficient
• optically active components
• coastal waters
• the Black Sea

Acknowledgements

Special thanks go to the leading engineer Ekaterina Zemlianskaia for help in laboratory processing of samples. Anonymous reviewers provided detailed comments that are gratefully acknowledged.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Additional information

Funding

Variability of spectral bio-optical properties of the Black Sea coastal waters in relation to water trophic status was analysed with the financial support of the Russian Science Foundation (project number 22-27-00790).