STRUCTURE AND TAXONOMIC DIVERSITY OF BENTHIC DIATOM ASSEMBLAGE IN A POLLUTED MARINE ENVIRONMENT (BALAKLAVA BAY, BLACK SEA)

摘要

The study examined changes in the structure and diversity of benthic diatom assemblages from 16 sampling stations covering Ca 0.3 km(2) of the bottom of industrially polluted Balaklava Bay (Crimea, Black Sea). We analyzed data on diatom abundance and species richness along with measurements of 15 variables: depth, sediment size structure, TOC, metals (Zn, Ni, Cu, Pb, Hg, Cd, Cr, Mn) and organochlorine toxicants (PAHs, pesticides, PCBs). Based on cluster and MDS analyses, two groups of stations were distinguished at 30% similarity level. The first group comprised stations in the inner, most polluted part, and the second corresponded to the outer part of the bay. Diatom assemblages of a certain structure arc formed within each group of stations. The species most responsible for similarity/dissimilarity within/between each of the distinguished complexes were determined and are listed. In total, 183 species representing 58 genera were identified. Species richness was highest in the genera Nitzschia Hassal (28 species), Amphora Ehrenberg (19), Navicula Bory (16), Cocconeis Ehrenberg (15), Diploneis Ehrenberg ex Cleve (11) and Lirella Karayeva (6). Our analyses showed that the combination of depth, percentage of sandy fraction, and the content of TOC, pesticides, PCBs and mercury exerted the most significant impact on diatom assemblage structure and diversity. Changes in benthic diatom taxonomic diversity were evaluated for each station on the basis of average taxonomic distinctness (Delta(+)) and variation of the TaxD Index (Delta(+)). The taxonomic structure of diatom assemblages in Balaklava Bay is less diverse than the average level expected from the Crimean regional inventory (539 species). The Delta(+) value (80.89) was lowest for the most polluted part of the bay, where species-rich branches of taxonomic tree structure prevailed. The diatom assemblage in the part less impacted had a higher Delta(+) value (82.86), closer to the expected average mode (83.67) for the entire Crimean coast. Overall the results highlight problems with the use of taxonomic diversity measures to detect the impact of adverse environmental conditions based on benthic diatom assemblages.