Effects of abiotic factors on the structure of fungal complexes in the pelagial of the Black and Azov Seas in summer 2019

In cruise 108 of R/V Professor Vodyanitsky (11.07-03.08.2019), comprehensive studies of pelagic ecosystems of the Black Sea and the Sea of Azov were carried out within the economic zone of the Russian Federation. The purpose of the work is to study the species composition and spatial distribution of cultivable marine microscopic fungi in relation to the physicochemical factors of seawater. In the Black Sea, 42 water samples were taken at 14 stations and in the Sea of Azov, 20 samples at 10 stations. In the Black Sea, water samples were taken in the surface layer (1 m), in thermocline (a water layer in which the temperature gradient differs sharply from the gradients above and below) and below thermocline. In the Sea of Azov, water samples were taken in the surface (0.5 m) and near-bottom (9-11 m) layers. The effects of the following environmental factors on the structure of fungal complexes were analyzed: depth, water temperature, pH, salinity, concentrations of O2, NO-2, NO-3, NH+4, Nорг, PO3-4, Рорг, Si . The data were processed using MS Excel and PRIMER® 5.2.8 statistical software package (the functions Similarity, BIOENV, CLUSTER, and MDS). In total, 35 species of fungi from 17 genera, 12 families, 11 orders and 6 classes of phylum Ascomycota were identified, and there was a group of Fungi spp. that were not identified. In the Black Sea, 35 species were identified, in the Sea of Azov, there were 8 species from 5 genera, 4 families, 4 orders, 3 classes, and a group of Fungi spp. All micromycete species found in the Sea of Azov were also present in the Black Sea. The highest frequency of occurrence was noted for the species Exophiala dermatitidis (17.0%), Cladosporium cladosporioides (23.1%), and Cladosporium sphaerospermum (35.4%). The similarity (according to the Bray-Curtis coefficient) of the mycobiota of the seas in terms of quantitative indices of species richness was 37.8%, and 40.0% in terms of the species composition. In the Black Sea, the number of fungal species varied from 25 to 27 in the water layers, with the average abundance ranging from 16643 to 17867 CFU/L. In the Sea of Azov, the number of species varied from 5 (surface layer) to 9 (bottom layer), with the average abundance being in the range of 7100-7500 CFU/L (see Table 2). For the stations of both the Black Sea and the Sea of Azov, coefficients of statistically significant Spearman's correlations were calculated. They were determined by the combinations of 4 variables: sampling depth and concentrations of NO-2, NO-3, Si (ρmax = 0.503-0.513). The cluster and nonmetric multidimensional scaling (MDS ordination) in two dimensions, based on similarity coefficients for 4 significant factors at the level of ρmax = 0.503, divided the stations into 3 groups. Group I consisted of coastal stations of the Caucasian coast and adjacent open waters, Group II included coastal and seaward marine stations of the northern and central parts of the Black Sea. Group III included all stations of the Sea of Azov. The Bray-Curtis similarity coefficients for the quantitative indicators of the fungal complexes varied from 34.1% (groups I and III) to 52.0% (groups I and II), and for the species structure they varied from 38.7 (groups I and III; 5 common species and the Fungi sp. group) to 58.8% (groups I and II; 14 common species and the Fungi sp. group). Groups I and II are in the Black Sea, their similarity coefficients are greater than 50%, and the habitat conditions are similar. Consequently, the mycocomplexes of these groups are divided conditionally. The MDS analysis yielded a graphical representation of the fungal abundance and the values of the determinant variables in the groups. The dependence of the number of species and the fungal abundance in the mycocomplexes of the groups in the Black Sea and the Sea of Azov on the values of the determinant abiotic variables was established: direct proportionality for depth and – 3 NO and inverse proportionality for – 2 NO and Si. The values of the obtained correlation coefficients are not very high, which indicates that the structure of mycocomplexes was additionally affected by the factors that were not taken into account in our study.

Keywords

Authors

References