Šilović, Tina
(2012)
Composition and dynamics of picophytoplankton in Adriatic sea with emphasis on cyanobacteria genus Synechococcus.
Doctoral thesis, Sveučilište u Zagrebu, Prirodoslovno-matematički fakultet.
Abstract
Picoplankton has an important influence on the structure and functioning of planktonic communities, as well as on the carbon cycle and balance in the system. Due to the lack of nutrients, picoplankton becomes the most important part of the biogeochemical cycle of circulation of elements and an important part of the food chain. Therefore, characterization of picoplankton is a key item for the deep understanding of marine ecosystems. Previous research of picoplankton in the Adriatic Sea was mainly focused on characterization of the genus Synechochoccus, while neglecting the eukaryotic component. Therefore, the main objective of this research is to provide a comprehensive picture of the Adriatic picophytoplankton community and to explain its dynamics at different temporal and spatial scales with relation to physical, chemical and biological parameters. This research presents the first results in the north Adriatic of flow cytometry analysis of picophytoplankton, as well as their diversity based on genetic analysis of 16S rRNA. The first recorded occurrences of Prochlorococcus in the north Adriatic were obtained, as well as the first appearence of particular Synechococcus strains. The dominance of the Synechococcus cyanobacteria in abundance and biomass, as well as in the structure of bacterial community, where it presented the most frequent taxon, confirms their utmost importance in the picoplankton community of the whole area. Picoeukaryotes were not that prominent in terms of abundance or biomass, but proved themselves as a stable and important compartment of the Adriatic phytoplankton community. The low abundances of Prochlorococcus recorded in the northern and the southern Adriatric indicated their minor importance in the picophytoplankton population and confirmed the mesotrophy of the area. In the southern Adriatic two ecotypes of cyanobacteria were recorded by flow cytometry, known as „dim“ and „light“, while genetic analysis of bacterioplancton in the northern Adriatic defined two different types of Synechococccus species, one very similar to the Synechococcus CC9902 strain, present in the surface and botttom layers, and another one similar to the Synechococcus WH7803 strain, present only in the surface layer. In conclusion, this study gives a more complete estimation of picoplankton dynamics in the Adriatic than it has been offered to date. Understanding system-specific environmental conditions and group tolerances to given conditions will improve our general concept of environmental control over different phytoplankton compartments.
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