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

Elena L Nevrova,Alexei N Petrov

doi:10.3906/bot-1903-43

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.

Highlights

The key role of Bacillariophyta in the primary production and functioning of marine ecosystems necessitates the study of benthic diatoms both to preserve their biodiversity and to use them in assessing the state of marine environment (Van Dyke 2008; Blanco et al, 2012; Rimet and Bouchez, 2012; Borja et al, 2013; Winter et al, 2013; Stenger-Kovacs et al, 2014; Nevrova et al, 2015; Keck et al, 2016)
Low species similarity between pristine and impacted biotopes may indicate a strong influence of sediment pollution on taxocenes structure, especially upon forms with low tolerance disappearing in polluted biotopes (Sevastopol Bay and Balaklava Bay)
Taxonomic distinctness indices provide more comprehensive insight into the architectonics of taxocenes, including in these metrics’ elements related to the hierarchical relationships among species that are important for a deeper understanding of the concept of biological diversity

Summary

Introduction

The key role of Bacillariophyta in the primary production and functioning of marine ecosystems necessitates the study of benthic diatoms both to preserve their biodiversity and to use them in assessing the state of marine environment (Van Dyke 2008; Blanco et al, 2012; Rimet and Bouchez, 2012; Borja et al, 2013; Winter et al, 2013; Stenger-Kovacs et al, 2014; Nevrova et al, 2015; Keck et al, 2016). Many coastal areas are subjected to increasing anthropogenic disturbance that causes significant changes in the species composition of benthic diatom taxocenes. Due to being fast-reproducing organisms, most diatoms are widespread on different substrates and are closely associated with a certain microbiotope; they may promptly indicate adverse changes in main biotopic conditions determined by natural environmental processes and anthropogenic impact (Stenger-Kovacs et al, 2014). Comparative analysis of the structure of benthic diatom taxocenes in pristine coastal habitats and in anthropogenically perturbed biotopes is an important basis for identifying various aspects of the formation and sustainability of Bacillariophyta diversity under changing environmental conditions (Petrov et al, 2005; 2010; Facca and Sfriso, 2007; Heino et al, 2007; Petrov and Nevrova, 2007; Leira et al, 2009; Stenger-Kovacs et al, 2014; 2016; Nevrova, 2015). The importance of considering biodiversity indices at the interregional scale receives an increasing emphasis for planning the

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