Macrozoobenthos of The Eastern Gulf of Finland: Current State and Influence on Biogeochemical Processes

Abstract

Macrozoobenthos plays an important role in biogeochemical processes. In the eastern part of the Gulf of Finland, macrozoobenthos has been changing rapidly in recent decades due to the massive development of alien species of annelids. The current state of benthic communities in the Gulf of Finland is considered based on data at 24 stations in 2019–2021. In open areas of the bay, the biomass of the bivalves Macoma balthica increased as compared to the beginning of the 2010s. The populations of glacial relict crustaceans, which had greatly decreased in the early 2000s due to benthic hypoxia, have practically recovered. The abundance of oligochaetes has also increased due to the spread of the alien species Tubificoides pseudogaster. This led to a decrease in the proportion of alien polychaetes Marenzelleria spp. in the abundance and biomass of macrozoobenthos. Due to differences between species in living and bioturbation activity, the changes that have occurred in the benthos should affect the processes at the water–bottom interface. There is likely to be an increase in the supply of phosphorus from bottom sediments under modern conditions compared to the period of total dominance of polychaetes in benthic communities in the early 2010s.