1. Korchemkina E. N.
   
   Marine Hydrophysical Institute of RAS, Sevastopol, Russian Federation (ru)
2. Ли Р. И. (Lee R. I.)
   
   ФИЦ «Институт биологии южных морей имени А. О. Ковалевского РАН»

Purpose. The purpose of the study is to describe the spatial distribution and structure of the phytoplankton community, and to reveal the relationships between the seawater optical characteristics and the phytoplankton abundance and biomass in the coastal waters of the Southern Coast of Crimea.

Methods and Results. The phytoplankton abundance and biomass were determined during the 127th cruise of R/V Professor Vodyanitsky by taking samples and their subsequent laboratory processing. Application of a semi-analytical algorithm made it possible to calculate simultaneously the phytoplankton pigment concentrations using the spectral reflectance coefficient of the sea measured from on board the ship. As for the species composition of phytoplankton, the water area under study was quite homogeneous: dinoflagellates, diatoms, and haptophytes were predominant in the phytoplankton community of the 0–10 m layer. It is shown that during the period of mass development of the haptophyte alga Gephyrocapsa huxleyi (Lohmann) P. Reinhardt 1972, its abundance dominated in the phytoplankton community, namely its contribution to the total abundance ranged from 30 to 70%. At the same time, the main part of wet biomass (42 to 98%) consisted of heterotrophic and mixotrophic forms of dinoflagellates. It was revealed that the phytoplankton pigment concentrations calculated using a semi-analytical algorithm correlated well with the biomass, but poorly with the cell abundance.

Conclusions. During the mass development of coccolithophores Gephyrocapsa huxleyi, a significant increase in light scattering accompanied by a slightly increased absorption complicates the description of the marine environment by optical methods. Under the specified conditions, assessing the phytoplankton pigment content, and later its biomass, is still possible.