Temporary dynamics of morphometric characteristics of phytoplankton in the coastal waters of the Crimea (Black Sea, Ukraine)
Authors:   M.G. Kholodny Institute of Botany NAS of Ukraine, 2 Tereschenkivska Str., Kyiv 01601, Ukraine, Bryantseva Yu.V. 
Published: January 2023

The morphometric characteristics of algae at different levels of hierarchical organization – cells, species, functional complexes of species, taxa (diatom algae, dinoflagellates) and phytoplankton as a whole were analyze. Study based on the results of monitoring carried out near the shores of Sevastopol (the Black Sea) in different periods (2004−2006 and 2009−2014), using the cells shape sphericity index (CSSI). It is shown that for each period there is a certain range of fluctuations of average values, both in seasonal and interannual dynamics. A comparison of the two investigated periods by the average CSSI showed a statistically significant decrease in diatoms and a slight increase in dinoflagellates, which may be associated with a shift in the species composition of diatom algae towards more elongated forms, and more rounded in dinoflagellates. Based on the example of two species with elongated cell forms: the diatom Proboscia alata (Brightwell) Sundström and the dinoflagellate Tripos furca (Ehrenberg) F.Gómez, as well as on the 3rd complex as a whole, a significant positive correlation with the water density on the surface was found with the 99% confidence level, which quantitatively confirms their seasonal polymorphism. The analysis of the seasonal dynamics of CSSI of diatoms as a whole showed statistically significant differences and a wide range of fluctuations by month. In the seasonal dynamics, three waves with an interval of four months were found, which corresponded to the seasonal course of the population quantity, except for the March bloom of the 2nd complex representatives belonging to the genus Pseudo-nitszchia H.Peragallo, as a result of which the CSSI was minimal. The May and September maxima of numbers corresponded to the maxima of the CSSI due to bloom and the development of the 1st complex representatives, mainly of the genus Chaetoceros Ehrenberg. For dinoflagellates seasonal differences were not significant and varied within a narrow range, with high mean values (above 0.94) for most of the year. The CSSI minima coincided with the population maxima in May and October. The range of CSSI fluctuations in the seasonal dynamics of diatoms (34.7%) was an order of magnitude higher than that of dinoflagellates (3.7%), which indicates a more stable grouping structure of the latter. Therefore, the average form depends to a large extent on species diversity. At the same time, diatoms are characterized by greater plasticity in adapting to environmental conditions. All phytoplankton are characterized by high CSSI values for most of the year due to the predominance of small flagellates and Prymnesiophyceae algae, with an episodic decrease during the period of diatom bloom in spring and autumn. The rounding of the grouping of both diatoms and dinoflagellates in 2010 May be a response to an abnormally high temperature of water, which led to the intensification of trophic processes in the marine environment. The obtained results can be used as a baseline for comparison in case of resumption of monitoring in this area in the future. The proposed method can be used as a basis for carrying out similar monitoring in any other water area of any type of reservoir.