Phytoplankton quantitative development and species diversity in the Bulgarian Black Sea waters during 2014-2017

Daniela Klisarova, Dimitar Gerdzhikov, Gergana Kostadinova, Diyana Dermendzhieva

Abstract: The aim of this study is to analyse the characteristics in the development of the phytoplankton communities in the Bulgarian part of Black Sea and in Varna Lake in present days, to trace the occurring changes and to assess their ecological status. During the study period (2014-2017), 196 phytoplankton samples were collected from 52 stations by bathometer type Niskin-5L. The samples were prepared for analysis (fixed and concentrated) and analyzed by routine methods. The analysis of the qualitative and quantitative structure of phytoplankton in the monitored areas revealed the existence of 182 phytoplankton species belonging to 14 taxonomic classes. The share of Dinophyceae/Bacillariophyceae group in the phytoplankton composition was 72.53%. A total of 8 species in the coastal and shelf zones and 7 species in the water of Varna Lake were found in bloom-causing concentrations. The highest quantities of phytoplankton were produced during the winter-spring period, with a trend toward increasing the numbers andphytoplankton biomass from 2014 to 2017. The ecological assessment based on results for the phytoplankton determined the ecological status of coastal and shelf water as “moderate” and the ecological status of Varna Lake water as “bad”.

Keywords: Black Sea; coast and shelf; ecological assessment; phytoplankton; phytoplankton structure; seasonal dynamics; Varna Lake

Date published: 2019-12-30