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Composition and abundance of picoplankton in the coastal zone of the Gulf of Gdańsk

Gławdel M., Mackiewicz T., Witek Z.

Oceanological Studies

1999

Vol. 28, No. 1-2

17-30

With the aid of epifluorescence microscopy, picoplankton (0.2-2mum) in the coastal zone of the Gulf of Gdansk (southern Baltic) was studied from March to December 1997. The main portion of the picoplankton biovolume was comprised of bacteria, making up on average 70% of picoplankton. Autotrophic picoplankton (APP) prevailed over the bacterioplankton only in late August and early September. The main components of APP were cyanobacteria. The APP proportion in the total phytoplankton biomass was highest in summer. The assessment of this share in terms of quantity varied depending on the picoplankton separation method. In the microscopic analysis of unfiltered samples, all cells 2mum were counted as picoplankton, including colony-forming types. Based on the analysis of unfiltered samples, the amount of APP in the overall phytoplankton biomass was assessed at 16-22% in summer, and 0.5-6% in the remaining period. Initial filtration of samples through a 2mum filter caused great losses in APP, resulting mainly in the elimination of colony-forming cyanobacteria cells from samples. Prefiltered samples were also contaminated by cells 2mum. In prefiltered samples the APP proportion in the total phytoplankton biomass was 1-7% in summer and 0.2-3% in the remaining period.

The impact of the River Odra on the phytoplankton composition and biomass in the Pomeranian Bay

Gromisz S., Witek Z., Mackiewicz T.

Oceanologia

1999

No. 41 (3)

403-427

The article is based on the analysis of phytoplankton samples collected in the Pomeranian Bay during five cruises in the years 1993, 1996 and 1997. In each season a number of phytoplankton assemblages were formed under the impact of the hydrological and hydrochemical conditions gradually changing along an axis from the outlets of the Szczecin Lagoon towards the open sea. The most distinct assemblages could be described as "river-mouth", "open-Bay"and "open-sea" assemblages. The highest phytoplankton biomass was noted near the mouth of the Swina Strait in the "river-mouth" assemblages, where the concentration of chlorophyll a was 4 to 5 five times higher in comparison with the "open-sea" values. The phytoplankton biomass in the "open-Bay" assemblages was roughly twice as high as that in the 'open-sea' assemblages. Because of the high N:P ratio in the Odra waters, phosphorus was very probably the factor limiting phytoplankton primary production in the Pomeranian Bay during periods of intensified inflow of riverine waters. The species dominating the phytoplankton of the Pomeranian Bay during the present study were found to be the same as those recorded in this region 40 years earlier.