Benthic diatoms (Bacillariophyta): diversity and hierarchical structure of taxocenes on soft bottom offkruglayabay (Black Sea, Crimea)
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Abstract
Kruglaya Bay (or Omega Bay) has a high recreational value due to its inland location in the Sevastopol region, long beach area and shallow water area with a sandy bottom. These features determine the need to control the state of marine biota. The aim of the work was to identify the current state of species richness and hierarchical structure of benthic diatoms in the Kruglaya Bay insufficiently studied before and also – to compare a foremented ones with coastal biotopes off Crimea under different levels of anthropogenic impact. Based on the results of benthic survey in 2004, the species richness of Bacillariophyta in Omega Bay was studied. The taxonomic diversity was analyzed on the basis of floristic and formalized methods using taxonomic distinctness indices (TaxDI). We identified 260 species and intraspecific taxa of benthic diatoms represented by 252 species, 69 genera, 35 families, 21 orders and 3 classes. We found 70 species and 5 genera new to the Black Sea flora of Bacillariophyta of the northern Black Sea shelf, as well as five species of diatoms described as new to science before. The greatest similarity in species composition was marked both between habitats with the lowest level of anthropogenic impact (Omega Bay — Dvuyakornaya Bay) and also between heavily polluted water areas (Sevastopol Bay — Karantinnaya Bay and Sevastopol Bay — Balaklava Bay), regardless of their remoteness and different distances from each other. Taxocenes of diatoms from heavily polluted regions are characterized by low species richness and a large proportion of mono- and oligospecies branches due to reduction of low pollutant-resistant taxa. The AvTD index values exceed the average expected level for the Black Sea flora of Bacillariophyta. In conditionally clean water areas, diatom taxocenes have high species richness, a large number of polyspecies branches and a small proportion of mono- and oligospecies branches which aggregating at different levels of the hierarchical tree. The values of AvTD index are below the average expected level for the Black Sea diatom flora. The peculiarities of diatom taxocenes structure from the compared regions are due to the species-specific response of different taxa to the joint impact of environmental factors. The use of TaxDI indices in the analysis of taxonomic diversity of Bacillariophyta allows statistically reliable assessment of marine coastal water areas with different pollution status.