Bulletin of the Sea Fisheries Institute 2 (153) 2001 - CEEMaR

BULLETIN O THE SEA ISHERIES INSTITUTE
2 (153) 2001
Main phytoplankton assemblages in the Gulf of Gdañsk
and the Pomeranian Bay from 1994 to 1997
S³awomira Gromisz and Zbigniew Witek
Sea isheries Institute, Ko³³¹taja 1, 81-332 Gdynia, Poland
Abstract. The comparison of the phytoplankton composition of 156 samples collected during 11
cruises in the Gulf of Gdañsk and the Pomeranian Bay based on clustering analyses led to the
identification of ten algae assemblages at a similarity lower than 50%. The most distinct phytoplankton
assemblages were found in samples collected at stations located directly near the Vistula
River mouth and a local, single-species assemblage formed by dinoflagellate Peridiniella catenata
in the Gulf of Gdañsk. Other assemblages were relevant to subsequent seasons of the vegetative
cycle: winter-spring, summer and autumn.
The relationship of the phytoplankton assemblage with environmental conditions (low salinity,
high nutrient concentrations) was the most evident near the Vistula River mouth. In other areas,
phytoplankton composition changed seasonally and was mainly correlated with temperature, and/
or day length. The differences in phytoplankton composition between the Gulf of Gdañsk and the
Pomeranian Bay were relatively small at a similarity higher than 50%.
Key words: phytoplankton, Baltic Sea, estuary, assemblages, diversity
INTRODUCTION
The Gulf of Gdañsk and the Pomeranian Bay are both of significant importance in the functioning
of the Baltic ecosystem. The Vistula River mouth is located in the Gulf of Gdañsk, and is
second only to the Newa River in the volume of freshwater it contributes to the Baltic Sea
(approximately 34 km 3 /year). The largest river mouth in the western region of the Baltic Sea is
that of the Oder, which contributes approximately 18 km 3 of freshwater annually. The nutrient
load carried by these two rivers comprises a significant portion of the total nutrient input to the
Baltic Sea. or example, the 1995 loads of total nitrogen and total phosphorus from both the
Vistula and Oder Rivers was 25% and 33%, respectively, of the total input of these elements to
the Baltic Sea from all land sources (excluding atmospheric input; HELCOM 1998).
Although the areas of the two basins are similar (Gulf of Gdañsk – about 5,000 km 2 ,
Pomeranian Bay – about 6,000 km 2 ), their topography and functioning differ. The Gulf of
Gdañsk is a relatively deep basin with a maximum depth of 117 m. It is permanently stratified
(halocline at depths of about 70-90 m) and organic matter accumulates in its sediments and