The monitoring of the phytoplankton condition in the Luga Bay of the Gulf of Finland under natural and anthropogenic impacts

Abstract

The technogenic transformation of the ecosystem of the southeast part of Luga Bay water area (the second bay of the Baltic Sea) where Ust-Luga commercial seaport situated was determined by longstanding dredging, dumping and other types of anthropogenic impact. The development of phytoplankton as the main primary production former and the base of food reserve for aquatic biological resources was investigated during the monitoring of aquatic biological resources of the Luga Bay which was held due to the seaport construction. The investigation of phytoplankton content and development took part in the main seasons of the ice-free period of 2005–2018 in the water areas of dredging, damping, and adjacent areas. The maximum values of the phytoplankton abundance and biomass were detected in spring. The main part of biomass was formed by diatoms and dinoflagellates. The summer biomass mainly was lower than in spring and the proportion of cyanoprokaryotes (in some years also cryptophytes and green) increased. In autumn the biomass decreasing was continued, cyanoprokaryotes and cryptomonads dominated. The quantitative indicators of phytoplankton development were varied from year to year in all seasons of 2005–2018 but they kept in frames of values which previously observed for the water area of the Luga Bay. The influence of the Gulf of Finland water warming on phytoplankton development was not traced. The certain differences between the quantitative development and composition of the dominant phytoplankton complex on the water areas of dredging, damping, and adjacent areas weren’t observed. The average phytoplankton biomass for the ice-free period in the most part of years corresponds to the mesotrophic state of the Luga Bay water area. There was not a significant impact of dredging and dumping on the phytoplankton of the Luga Bay which indicates the stable state of its ecosystem primary producer and the preservation of the productional resource of the fish food base.