Bibliotheca Diatomologica, Volume 28: Recent and Fossil Diatom Flora of the Gulf of Gdańsk, Southern Baltic Sea

The aim of this study is to analyze the species composition of recent, subfossil and fossil diatom floras in the Gulf of Gdańsk (Zatoka Gdańska, Danziger Bucht) in the southern Baltic Sea. The diatom assemblages of extant bottom sediments are compared with those from fossil deposits. Within the recent flora of the study area, 423 taxa (species and varieties) belonging to 65 genera were identified. For each taxon the ecological preferences and the distribution within the study area are indicated.

With respect to the salinity requirements, brackish-water and marine forms are significantly predominant. The proportion of freshwater flora varies, being large close to the mouth of the Wisła, and insignificant in the remaining area. The diatom flora of the gulf area is differentiated into several assemblages. Unique to the whole of the Baltic Sea is an anthropogenic assemblage, which species composition is modelled by waste water entering the study area with the Wisła run-off.

It is shown that the diatom flora of the study area underwent three significant shifts in the course of the Holocene. The first and the second were connected with changes in the salinity, occurring at the beginning (increase) and at the end (decrease) of the Litorina stage. Recent changes in the diatom flora of the gulf area have been caused by an increasing pollutant load. The least pollution tolerant taxa are replaced by the most resistant ones. A study of the subfossil material enabled the vertical extent of anthropogenic changes in the diatom species composition to be determined.

The recent flora is compared with the subfossil and fossil ones from sediments. A group of 22 marine taxa is indicated as extinct in the study area. Based upon their distribution in the western Baltic, the salinity of the Gulf of Gdańsk during the Litorina stage is determined.