Assessment of the ecological state of the Danube delta coastal area (northwestern part of the Black Sea) based on meiobenthos and nematode assemblages

Abstract

The suitability of using meiobenthic communities and especially the nematodes-based indices to assess the ecological quality of the Ukrainian Danube delta coastal area was tested in one control and two sites impacted by dredging/dumping activities. The study is based on the results of benthic surveys carried out in November 2015 and August 2018 and 2020 in the area of the “Danube-Black Sea” navigable canal. The values of the taxonomic richness of the meiobenthos varied from 6 taxa in the dredging sites to 9 taxa at background stations. According to the species richness, the ecological quality in the dredging area fell into the Poor class (EQS), while the background and dumping areas into the Moderate class.
TThe Shannon index (H‘) of the nematodes in the dredging sites varied from 0 to 1.8. Low values of these indices indicate Bad ecological status in the dredging sites and Poor in the rest. There was a high percentage of c-p2 (r-strategists) in all sites. Average values of the maturity index (MI) varied from 1.5 ± 0.2 in the dredging sites to 2.3 ± 0.1 at dumping and 2.6 ± 0.1 at background stations. The Maturity Index also indicates that the dredging site is in Bad condition, the dumping one is in Poor and the background stations are in Moderate.
Non-selective deposit feeders (1B) dominated at most stations. According to the values of the trophic diversity index (ITD), the study area can be classified as Poor. For the study sites, species that can be considered potential biological indicators are evinced.