engleski

Group specific phytoplankton biomass/dissolved carbohydrate relationships in the northern Adriatic

Despite the fact that carbohydrates (CHO) play a major role in the hypertrophic appearance of gelatinous aggregates in the northern Adriatic a very little is known about their origin, distribution and fate in that vulnerable ecosystem, especially about their relationship to the group specific biomass. The aim of this study was to investigate the relationship between photosynthetic pigments, reflecting phytoplankton dynamics, and CHO in the northern Adriatic. Sampling strategies involved drifter experiments, as well as determination of temporal and spatial variability at fixed stations. Chlorophyll and carotenoid pigments were determined by RP HPLC, while CHO were measured spectrophotometrically by MBTH-method. It was shown that an increase of the CHO concentrations was associated with the particular type of phytoplankton blooms rather than with an enhancement of the chl a concentration in general. The major phytoplankton blooms occured in the surface layer after the freshets in spring and autumn and were mostly dominated by diatoms, more seldom by pymnesiophytes. In contrast, intensive blooms in the bottom layer were detected only sporadically and consisted of dinoflagellates and silicoflagellates. The total carbohydrate (TCHO) levels in the water column of the northern Adriatic were relatively low, rarely exceeding 350 ľg C /l. However, a pronounced increase of TCHO concentration (up to 1325 ľg C/l) was noticed during diatom and dinoflagellate blooms, indicating a significant contribution of microphytoplankton as a source of CHO. In most of the situations CHO represented less than 20 % of DOC, exceptionally during diatom and dinoflagellate blooms their contribution reached up to 90 %. Dissolved carbohydrates (DCHO) were found mainly in the form of polysaccharides which contributed to the total DCHO by 30-96 %. Physiological status of the phytoplankton biomass, as indicated by chlorophyll break-down products, exerted a significant impact on TCHO levels.

phytoplankton; pigments; carbohydrates; north Adriatic

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