Recommendations for Using the Method of Standards in Bioindication Studies of the Northern Caspian Sea

Despite the increasing water and sediment pollution in the western part of the Northern Caspian Sea, the quality of its marine environment has never been assessed through bioindication, largely due to methodological issues. In this article, the method of standards, which involves comparing the species composition between the polluted and clean (reference) sites, was used for the bioindication of organic pollutants in the Northern Caspian Sea. The study area was segmented based on isobaths. The segments were determined depending on the range of depths inhabited by zoobenthos species and their ecological valence to oxygen. The depths with a sufficient abundance of oxyphilic zooplankton species (bioindicators) to apply the method of standards were located. The obtained results show that the method of standards is good and reliable choice to assess the marine environment quality in the Northern Caspian Sea at isobaths of 6-9 m and within depths of 14-18 m for polluted and reference sites. However, the sediments must contain shells, sand, and siltstones. Therefore, while the method of standards has clear merits, it does not suffice for the rest of the Caspian Sea area.