ASSESSMENT OF THE ENVIRONMENTAL STATE OF THE BLACK SEA COASTAL WATERS BY BIOINDICATION METHODS

. Using bioindication methods, the authors assessed the environmental state of water at the place where the Hadzhiyska River flows into the Black Sea (Slanchev Bryag / Sunny Beach resort, Bulgaria). Methods. The studies were carried out in the summer seasons of 2017–2019 during sea water “blooming”. The quality of river water was assessed by the state of the community of zoobenthic organisms using the Trent biotic index originally developed by Woodiwiss and the Mayer index, and the state of the coastal marine ecosystem was assessed by the species composition of the Black Sea macroalgae. Results. The waters at the mouth of the Hadzhiyska River can be classified as “polluted” and represent the main local source of biogenic elements entering the coastal sea waters. In the marine macrophytobenthos, representatives of green, brown and red algae were identified, including two species listed in the Red Book of the Black Sea — Cystoseira barbata and Zostera marina. The authors noted a displacement of native species — representatives of Cystoseira and Zostera genera — due to an increase in the number of associated algae from Ceramium, Cladophora and Ulva genera, which confirms organic pollution and eutrophication in coastal waters. The taxonomic structure of the macrophytes allows for the conclusion that the environmental state of the marine ecosystem in the area is satisfactory. The authors also provide a rationale for the use of benthic organisms in the express diagnostics of water environment quality in resort areas.