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Pico- and nano autotrophic community in the Lim bay (NE Adriatic Sea)

This work describes the dynamics of autotrophic pico- and nanoplankton community at three distant stations in the Lim Bay, a 12 km long embayment situated on the western part of the Istrian peninsula, north-eastern part of Adriatic Sea. The known shortcomings of routine microscope procedures in picophytoplankton characterization, directed us to the next step, the flow cytometry implementation in our picoplankton research. The community structure of picophytoplankton was dominated by phycoerythrin-rich cyanobacteria of the Synechococcus type with highest abundances in summer (July), while their presence was negligible in autumn (November), in the period of high microphytoplankton concentrations. Autotrophic picoeukaryotes were present in higher abundances in the bottom parts of all sampling stations and reached their maximum values in August. The nanophytoplankton abundances were generally low, except in June when their numbers were the highest, especially in the surface layer. Although, the autotrophic size structure differed among sampling stations and throughout the water column during the investigation period, a domination of picoplankton (size class <2 um) was generally observed. The significant correlations between microscopy and flow cytometry analysis data were achieved for populations of picocyanobacteria (p<0.01, R2=0.5), nanophytoplankton (p<0.01, R2=0.4), and for picoeukaryotes (p<0.01, R2=0.3) it was significant but moderate. Nanophytoplankton counted by inverted microscope showed no correlations with epifluorescence microscope or flow cytometry counts at all. This research represents the initial using of novel flow cytometry technique for the characterization of the autotrophic picoplankton population dynamics in the Lim Bay, and provides precise evaluation of picoeukaryotes population structure/dynamics in this area while indicating their importance as a consistent component of the phytoplankton community.

picoplankton; nanoplankton; flow cytometry; northern Adriatic

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