Denis Lishaev

Rocky seabeds, as an integral part of ecotopes in marine ecosystems, are actively inhabited by diatoms and cyanobacteria. It is currently unknown whether the element contents in the surface layer of seabed rocks affect the epilithon species composition and abundance in microphytobenthos communities in the sea. The results of this study on the rock surface element composition and correlation analysis of the element contents with the abundance of epilithon diatoms and cyanobacteria in three bays in Sevastopol (Black Sea) are presented. Ca, Fe, and Si were the major elements with the largest weight fraction in the rock surface layer. Using cluster analysis, the differentiation of samples in the content and distribution of these three elements was shown. In total, 63 taxa of diatoms and 20 species of cyanobacteria were found, with their abundance ranging from 14,000 to 17,6000 cells/cm² and from 12,000 to 1,198,000 cells/cm², respectively. In general, it was found that the elemental composition of the rock surface is not a decisive factor affecting the total abundance of the benthic diatom and cyanobacterial communities as no strong correlations with any element contents were observed. However, when analyzing the abundance of populations of certain largely non-dominant species, the majority of diatoms showed noticeable (r = 0.5–0.7) to very high (r = 0.9–0.99) correlations with Fe. The highest positive correlations were noted for the diatoms Bacillaria paxillifer and Navicula directa with Fe. For the cyanobacteria Chroococcus minutus, Pseudanabaena minima, and Spirulina subsalsa, strong positive correlations with Ca and negative correlations with Si were observed. The correlations with Fe were very strong and negative for Lyngbya confervoides and strong and positive for Kamptonema laetevirens and Phormidium holdenii.

For the first time in the Kruglaya Bay of the Black Sea, 25 taxa of Bacillariophyta from 17 genera were found, three of them were new for the Crimea and the Black Sea Halamphora tenerrima , Amphora tenuissima , and Navicula antonii . Marine (40%), coastalbrackish (32%) and boreal-tropical (32%), arctic-boreal-tropical (24%), boreal and cosmopolitan (20% and 16%, respectively) prevailed. The morphological characteristics of the species in the SEM (scanning electronic microscope) and LM (light microscope), as well as the occurrence, ecology, phytogeography, and general distribution in various regions of the World Ocean are given.

Analysis of long-term data (1987–2019) was carried out on the morphology and autecology of the benthic colonial large-cell species Striatella unipunctata (Lyngbye) C. A. Agardh, 1832 in the microphytobenthos of the Black Sea and Sea of Japan, including water areas of specially protected natural areas of Russia. The species is widely found on natural and artificial substrates in the Black Sea year-round, and in the Sea of Japan, at a water temperature down to −1.5 °C. St. unipunctata quantitative data were determined by direct cell counting in the Goryaev camera under light microscopes (LMs) Biolam L-212, Axioskop 40, and Olympus BX41. Species morphology, phytogeography, and ecology are described. The cell size range of populations is presented: for the Black Sea, valves 25–148 µm long, 8–22 µm wide, frustules 36.3–50.4 µm wide, 18–24 fibulae in 10 µm, and 7–8 girdle bands in 10 µm; for the Sea of Japan, valves 85–125 µm long, 12–21 µm wide, 7–8 girdle bands in 10 µm, 20–25 fibulae in 10 µm, frustules 32.0–34.3 µm long, 10–11 µm wide, and 25 fibulae in 10 µm. For the first time, St. unipunctata valves and frustules were studied in vivo under LMs, and frustule ultrastructure, under a scanning electron microscope (SEM). For the first time, quantitative indicators of the species populations from the Black Sea and Sea of Japan were compared. The morphology of the frustule ultrastructure of St. unipunctata was studied under a Hitachi SEM, model SU3500 (Japan), in Leica EM ACE200 gold-palladium-coated samples. In the Kazachya Bay of the Black Sea near the Oceanarium, the absolute maximum abundance was recorded – 41.6·10³ cells·cm−2 with a biomass of 1.73 mg·cm−2 in January (t = +6.9 °C) in the epizoon of the cultured mussel Mytilus galloprovincialis Lamarck, 1819 at a depth of 0.5 m at excessive organic pollution of water. The minimum values were of 0.26·10³ cells·cm−2 and 0.011 mg·cm−2, respectively, in July (t = +23.5 °C) at a depth of 2.5 m. In the Paris Bay (Russky Island) of the Sea of Japan in the water area of the Marine Mammal Research Base of the Primorsky Oceanarium (Vladivostok), the abundance in the asbestos plates periphyton was of 207·10³ cells·cm−2 in the summer. For the first time, unique micrographs of the species in vivo were obtained under a LM, and of purified frustules – under a SEM.

In this work, the species diversity of epilithon diatoms of Donuzlav Gulf (Crimean coastal waters of the Black Sea) is presented for the first time. A total of 60 taxa of Bacillariophyta belonging to 3 classes, 18 families and 34 genera were found. The largest number of species (45) of diatoms was observed in summer, and the smallest number of species (12) in winter. A total of 25 saprobity indicator species of diatoms was found on the epilithon, 12 taxa of which belong to a group of betamesosaprobionts—indicators of moderate organic pollution of water. Marine species comprise 55% and brackish-marine ones make up 37% of them, but no freshwater species were identified. The diatom community was dominated by cosmopolites (32%) and arctic–boreal–tropical species (27%). The maximal abundance (186.2 × 10³ cells cm⁻²) and biomass (0.083 mg cm⁻²) of diatoms was noted in June 2018 at salinity 16.58‰ and T = 24.4 °C with the dominant cosmopolites species of Licmophora abbreviata and Cocconeis scutellum. The minimum values, 14.8 × 10³ cells cm⁻² and 0.005 mg cm⁻², were observed in January 2019 at salinity 16.86‰ and T = 9.0 °C with the dominant Berkeleya rutilans and Nitzschia hybrida f. hyalina. The high values of BOD₅, oxidizability, silicon, N_org and P_org were noted, indicating a certain degree of water pollution by domestic sewage. It has been shown that the pollution in the southwestern part of the Donuzlav Gulf is greatest since this part of the coast was populated most densely in comparison with the northern coast of the Gulf where there are no coastal settlements except for two mariculture farms.