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Impact of environmental factors on phytoplankton composition and their marker pigments in the northern Adriatic Sea

Eker-Develi Elif, Berthon Jean-François, Free Gary

Oceanologia

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2022

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No. 64 (4)

615--630

EN

Phytoplankton composition, abundance and carbon biomass were investigated at monthly intervals during 2006–2007 at a coastal site, “Acqua Alta” an oceanographic tower, in the northern Adriatic Sea. Results were compared with chlorophyll a concentrations of phytoplankton classes attributed by HPLC-CHEMTAX analysis. Changes in the taxonomic structure were associated with environmental parameters. The total carbon biomass of phytoplankton was positively correlated with the temperature and negatively correlated with silicate concentrations. Nutrient concentrations were higher in the winter–spring period than in the summer-autumn period. The highest carbon biomass and abundance of phytoplankton were observed during summer–autumn months. Diatoms were the group that had the highest contribution to the total carbon biomass during the sampling period. Small flagellates, which were the major contributors to the total cell counts were dominant during the summer period. There was a significant correlation between carbon biomass and CHEMTAX-derived Chl a values of diatoms and dinoflagellates. However, the total carbon biomass of phytoplankton was not correlated with Chl a, which seemed to be related to seasonal changes in the ratios of C:Chl a of all taxonomic classes. This ratio was higher during the summer-autumn period (73 ± 33) than during the winter–spring period (17 ± 20).

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Microbial plankton communities in the coastal southeastern Black Sea : biomass, composition and trophic interactions

Aytan U., Feyzioglu A. M., Valente A., Agirbas E., Fileman E. S.

Oceanologia

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2018

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No. 60 (2)

139--152

EN

We investigated biomass and composition of the pico-, nano- and microplankton communities in a coastal station of the southeastern Black Sea during 2011. We also examined trophic interactions within these communities from size-fractionated dilution experiments in February, June and December. Autotrophic and heterotrophic biomasses showed similar seasonal trends, with a peak in June, but heterotrophs dominated throughout the year. Autotrophic biomass was mainly comprised by nanoflagellates and diatoms in the first half of the year, and by dinoflagellates and Synechococcus spp. in the second half. Heterotrophic biomass was mostly dominated by heterotrophic bacteria, followed by nanoflagellates and microzooplankton. Dilution experiments suggest that nano- and microzooplankton were significant consumers of autotrophs and heterotrophic bacteria. More than 100% of bacterial production was consumed by grazers in all experiments, while 46%, 21% and 30% of daily primary production were consumed in February, June and December, respectively. In February, autotrophs were the main carbon source, but in December, it was heterotrophic bacteria. An intermediate situation was observed in June, with similar carbon flows from autotrophs and heterotrophic bacteria. Size-fraction dilution experiments suggested that heterotrophic nanoflagellates are an important link between the high heterotrophic bacterial biomass and microzooplankton. In summary, these results indicate that nano- and microzooplankton were responsible for comprising a significant fraction of total microbial plankton biomass, standing stocks, growth and grazing processes. This suggests that in 2011, the microbial food web was an important compartment of the planktonic food web in the coastal southeastern Black Sea.

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Response of picophytoplankton to a warm eddy in the northern South China Sea

Wang J., Tan Y., Huang L., Ke Z., Tan J., Hu Z., Wang Q.

Oceanological and Hydrobiological Studies

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2016

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Vol. 45, No. 2

145--158

EN

We investigated the distribution of several picophytoplankton groups (Prochlorococcus, Synechococcus, and picoeukaryotes) in relation to a warm eddy in the northern South China Sea in summer 2012. An anticyclonic eddy centered on 117°E longitude was identi ed during the sampling period using satellite data and hydrologic mapping. e layer of maximum Prochlorococcus and Synechococcus abundance within the eddy core dropped from 50 to 75 m, which was consistent with the subsurface chlorophyll a maximum. e water-column integrated abundance of Prochlorococcus, Synechococcus, and picoeukaryotes in the eddy core (9.67±0.23, 1.56±0.04, and 0.28±0.01 × 103 cells ml-1, respectively) was signi cantly lower (P<0.05) than that of the reference stations (25.10±2.32, 2.71±0.63, and 0.92±0.15 × 103 cells ml-1, respectively), and the abundance of Prochlorococcus in the core was also signi cantly lower than that at eddy edges (15.75±1.78 × 103 cells ml-1). However, there were no di erences in the water-column integrated Chl a between the eddy core and edge. Our ndings show that the warm eddy led to the reduced picophytoplankton abundance, especially of Prochlorococcus and picoeukaryotes, causing the layer of maximum picophytoplankton abundance to differ from that of the subsurface Chl a maximum.

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Phytoplankton size structure and species composition as an indicator of trophic status in transitional ecosystems: the case study of a Mediterranean fjord-like karstic bay

Bosak S., Šilović T., Ljubešić Z., Kušpilić G., Pestorić B., Krivokapić S., Viličić D.

Oceanologia

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2012

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No. 54 (2)

255-286

EN

The species composition and size-structure of the phytoplankton community in the Boka Kotorska Bay (SE Adriatic Sea) were analysed with respect to abundance and carbon biomass, together with the physico-chemical parameters, with the aim of evaluating the predefined oligo-mesotrophic status of this transitional water ecosystem. Three stations located in the inner part of the Bay were sampled with seasonal frequency in 2008/2009. Picophytoplankton cells were counted using flow cytometry; nanophytoplankton and microphytoplankton were identified and counted by light microscopy. The relative importance of the picoplankton in the Bay, in terms of both abundance and biomass, during all the investigated seasons emphasized their significance in the phytoplankton community. Picocyanobacteria (Synechococcus) constituted a significant part of the summer assemblages with regard to both abundance (up to 3.38 × 108 cells L-1) and carbon biomass (up to 73% of total phytoplankton carbon). The contribution of the nanophytoplankton was found to be generally low (< 20% of the total phytoplankton carbon) in all seasons, and was dominated by autotrophic/mixotrophic flagellates. Species with a preference towards nutrient-enriched conditions, like the diatom Skeletonema marinoi, dominated the microphytoplankton fraction. S. marinoi was the most abundant in spring/winter (up to 2.86 × 106 cells L-1) above the halocline (making a 96% contribution to the microphytoplankton). The potentially toxin-producing diatom Pseudo-nitzschia pseudodelicatissima was recorded at abundances greater than 105 cells L-1, together with Thalassionema frauenfeldii, as well as the dinoflagellates Prorocentrum micans and the potentially harmful P. minimum. The higher values of phytoplankton biomass and the dominance of phytoplankton species or groups with preferences for nutrient-enriched conditions appear to be consistent with the oligo-mesotrophic status of this specific ecosystem.