Expedition on R/V Titov on May 24-28, 2025
On May 24-28, 2025, within the project of the RRF № 23-14-00028 “Microeukaryote Communities in Reservoirs of the Angara Cascade” (led by Likhoshway Ye.V.), a research expedition was carried out on the R/V Titov in order to compare the diversity of microeukaryotes in South Baikal (SB) and Irkutsk reservoir (IR) in the spring. Water samples were taken from the photic layer (up to 25 m in SB and up to 5 or 10 m in IR) using the Niskin bathometer at 9 SB stations (12 km from Kultuk, 3 km from Marituy, Marituy-Solzan, 3 km from Solzan, Tolstyi-Snezhnaya, 3 km from Tankhoy, Kadilny-Mishikha, Listvyanka-Tankhoy, 3 km from Listvyanka) and at 8 IR stations, including bays (Kurma, Elovy, Ershovsky). Water transparency was determined by a Secchi disk. After measuring the temperature, pH and electrical conductivity (EC) of the water, samples were collected on filters for further studing of samples by scanning electron microscopy (SEM), quantitative analysis of phytoplankton composition by light microscopy (LM), and extraction of DNA for sequencing to determine the taxonomic composition of microeukaryotes and by a Juday net for culturing microalgae species.
The expedition revealed that at the time of sampling, SB and IR differed from each other in terms of habitat characteristics and differed from May 2024: in SB, water was more transparent - 10-23 m compared with May 2024 - 9,5-13 m and warmer - 4.1-4.8 versus 2.5-3.2 °C in 2024. In IR, the water temperature was also higher up to 12.9 °C compared to May 2024 - 9.8 °С and less transparent - 6-13 versus 4-10.5 m in 2024. In the central part currentwise the river Angara from the source to the dam, the temperature of the surface water layer increased from 6.3 to 11.16 °C, while in May 2024 it ranged from 3.65 to 4.1-5.7 °C. The pH of the surface water layer in SB was 6.89-7.4, in IR was up to 6.82-7.49. In May 2024, the pH values in SB were higher - 8.03-8.38, and IR - 8.1-8.52.
Preliminary analysis of the sampled samples using LM revealed similarities in both the quantity and species composition of phytoplankton in SB and IR compared to the data of 2024. Phytoplankton of SB and IR are mainly represented by diatoms, chrysophytes and green microalgae. The dominated diatoms were Fragilaria radians (Kützing) D.M.Williams & Round, Ulnaria acus (Kützing) Aboal, Nitzschia graciliformis Lange-Bertalot & Simonsen, Stephanodiscus meyeri Genkal & Popovskaya and chrysophyte Dinobryon cylindricum O.E. Imhof. Phytoplankton of IR bays was generally similar to phytoplankton of the central part of the reservoir, but it was more abundant. The dominated diatoms were Fragilaria radians (Kützing) D.M.Williams & Round, Ulnaria acus (Kützing) Aboal, Nitzschia graciliformis Lange-Bertalot & Simonsen. Ulnaria danica (Kützing) Compère & Bukhtiyarova и Asterionella formosa Hassall Hassall were also found in Eroshovy Bay.
The data are preliminary and samples will be examined using LM and SEM. The total DNA for each sample will be extracted and the taxonomic composition of the bacterio- and phytoplankton communities analyzed using the high-throughput sequencing method.
The participants of the RSF project took part in the expedition: senior researcher, Cand. (Biology) Sc., Yu.P. Galachyants, senior researcher, Cand. (Biology) Sc., D.P. Petrova, engineer M.A. Nalimova. The expedition participants thank the RV Titov team for their good, well-coordinated work.
Photos of some species of algae taken using light microscopy. 1 - Asterionella formosa Hassall; 2 - Lindavia baicalensis (Skvortsov & K.I.Meyer) Nakov, Guillory, M.L.Julius, E.C.Theriot & A.J.Alverson; 3, 5 - Dinobryon cylindricum var. palustre Lemmermann; 4 - Monoraphidium griffithii (Berkeley) Komárková-Legnerová; 6 - Monoraphidium contortum (Thuret) Komárková-Legnerová; 7 - Aulacoseira islandica (O.Müller) Simonsen; 8 - Nitzschia graciliformis Lange-Bertalot & Simonsen; 9 - Fragilaria radians (Kützing) D.M.Williams & Round/Ulnaria acus (Kützing) Aboal; 10 - Ulnaria danica (Kützing) Compère & Bukhtiyarova; 11 - Monoraphidium komarkovae Nygaard. Масштабная линейка 10 мкм.
