engleski

Effects of mucilage event on the distribution of summer phytoplankton as reflected by phytoplankton pigments

Background and purpose: HPLC analyses of phytoplankton pigments are used for qualitative ans quantitative determination of phytoplankton groups in the sea. The scope of our study was to investigate the phytoplankton distribution from the early spring to early autumn in the year when mucilage appeared (1997) and the years without the mucilage event (1994, 1998) using pigment biomarker approach. Materials and methods: The qualitative and quantitative analyses of pigments (chlorophyll and carotenoid pigments, as well as breakdown products of chlorophyll a) were determined using reversed-phase high-performance liquid chromatography (RP HPLC) equipped with serially cuopled spectrophotometric and spectrofluorimetric detectors. Results: The chlorophyll a concentrations varied mostly between 100 and 1500 ng/l. 1994 and 1998 were characterized by spring and autumn peaks of phytobiomass with the highest values found in the surface layersm while during summer periods elevated chl a levels were typically found in the deepest layer (20 m). On the other hand, in 1997 we did not observe the classical spring peak of chl a in the surface layer, but the accumulation of phytoplankton biomass was observed in June and Jully at the depth of 15 m. The most abundant biomarker pigments, fucoxanthin and 19'-hexanoyloxyfucoxanthin, indicated prevalence of diatoms and prymnesiophytes, varying in ranges 15-2412 ng/l and less 2-1010 ng/l. The concentrations of fuc and hex showed elevated leevls in deeper layers during the summers of 1994 and 1998 as compared to the upper parts of the water column, while during period July-October 1997 the concentrations of hex in the bottom layer were mostly below detection limit. Other biomarker pigments were present usually at low concentration bellow 100 ng/l, with some exception for zeaxanthin+lutein and peridinin. Compared with 1994 and 1998, the 1997 showed an enhanced percentage of nano-(primnesiophytes) and picoplankton (cyanobacteria) in upper layers during the April-June period, and a very strong predominance of diatoms in the bottom layer. The concentrations of breakdown products, were higher in 1997 in respect to 1994 and 1998. Conclusion: Photosynthetic pigments composition reflected the impact of mucilage event on the distribution of summer phytoplankton.

phytoplankton ; photosynthetic pigments ; mucilage ; HPLC ; northern Adriatic

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