Assessment of benthic diatoms taxonomic diversity at coastal biotopes with different anthropogenic impact (Crimea, the Black Sea)

Authors: ELENA NEVROVA, ALEXEI PETROV

Abstract: An analysis of the taxonomic diversity of benthic diatoms was carried out for near-shore biotopes of Crimea with different content of trace metals and organic pollutants (PCBs, PAHs, DDTs). Taxonomic distinctness indices such as average taxonomic distinctness, AvTD (Δ⁺) and variation in taxonomic distinctness, VarTD (Λ⁺) were used for evaluation of the hierarchical structure of diatom taxocenes of two intact sites (Dvuyakornaya Bay and Cape Fiolent) and two heavily polluted water areas (Sevastopol Bay and Balaklava Bay). The highest similarity of species was revealed between healthy biotopes, in spite of their differences in hydrological and hydrochemical conditions. AvTD values for Dvuyakornaya Bay and Cape Fiolent (Δ⁺ = 79.0 and 76.7, respectively) were lower in comparison with expected average levels (Δ⁺ = 82.2) evaluated for the flora of benthic Bacillariophyta (1094 species) registered for the Northern part of the Black Sea (NPBS). As established, the taxonomic trees of the diatom taxocenes at pristine water areas are characterized by a moderate degree of vertical evenness and high variability of distances between neighboring clusters of species; they are mainly formed by polyspecific branches close on the genus level. The AvTD values for diatom taxocenes of the heavily polluted Sevastopol Bay (Δ⁺ = 83.6) and Balaklava Bay (Δ⁺ = 84.1) were significantly higher than the corresponding indices for undisturbed biotopes and exceeded the expected average level for the entire list of Bacillariophyta for NPBS. The upward trend of AvTD along the increasing technogenic impact can be caused by the disappearance of taxonomically close species with low tolerance from the same genus and prevalence of oligo- and monospecies branches in architectonics of the hierarchical tree. The present study shows that the application of TaxD indices can be considered an additional appropriate indicator tool for quantifying changes in the hierarchical structure of diatom taxocenes under persistent anthropogenic stress.

Keywords: Benthic diatoms, Bacillariophyta, hierarchical structure, taxonomic indices, average taxonomic distinctness, variation in taxonomic distinctness, pollution, Crimea, Black Sea

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