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

Abstract

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