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

100%

Glawdel M., Mackiewicz T., Witek Z.

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.

Experimental studies in processes taking place in enclosures with mixed sea and Vistula River water

64%

Witek Z., Pastuszak M., Nakonieczny J., Ochocki S., Zalewski M., Maciejowska M., Gromisz S., Mackiewicz T., Wrzesinska-Kwiecien M.

vol. 26

issue 1

35-57

Biological and chemical processes occurring in seawater from the Gulf of Gdansk, 'enriched' with Vistula river water, were studied in a series of microcosm experiments covering different seasons of the year. Concentrations of inorganic forms of nitrogen were, with one exception, 25 - 800 times higher in the Vistula water than those in the sea; phosphates were from 3.5 to 70 times higher. Two phases were observed during the incubations: during the first there were marked increases in primary production, chlorophyll concentration and bacterial production, and a de-crease in nutrient concentrations. The second phase was characterised by a lack of phosphates, a gradual decrease in chlorophyll concentrations, and an increase in zooplankton abundance. During the growing season the first phase lasted only a few days, during which nitrates and silicates were taken up at a rate of 2-4 mmol?dm-3?d-1 and phosphates and ammonia at a rate of 0.05-0.3 mmol?dm-3?d-1. Further phytoplankton growth and further nutrient uptake were most frequently limited by phosphorus depletion. Phosphorus was probably also a factor limiting bacte-rioplankton growth, which appeared to be correlated with primary production. In spring and autumn phytoplankton growth was additionally limited due to grazing by protozooplankton and rotifers, in summer by nitrogen exhaustion.

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2 Oceanological Studies

1 1999

1 1997

2 Mackiewicz T.

2 Witek Z.

1 Glawdel M.

1 Gromisz S.

1 Maciejowska M.

1 Nakonieczny J.

1 Ochocki S.

1 Pastuszak M.

1 Wrzesinska-Kwiecien M.

1 Zalewski M.

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

Experimental studies in processes taking place in enclosures with mixed sea and Vistula River water