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Identifier 000426317
Title Ευκαρυωτικό μικροβιακό πλαγκτόν και παροχή θρεπτικών στην Ανατολική Μεσόγειο
Alternative Title Eukaryotic microbial plankton and nutrient supply in the Eastern Mediterranean Sea
Author Σαντή, Ιουλία Σ.
Thesis advisor Καρακάσης, Ιωάννης
Reviewer Κασαπίδης, Παναγιώτης
Πήττα, Παρασκευή
Λαδουκάκης, Εμμανουήλ
Λύκα, Κωνσταντίνα
Παφίλης, Ευάγγελος
Ψαρρά, Στυλιανή
Abstract Marine microbial eukaryotes have crucial roles in the water column ecosystem; however, there are regional gaps in the investigation of natural microbial eukaryote communities and uncertainties concerning their distribution persevere. This study combined 18S rRNA metabarcoding, biomass measurements and statistical analyses of multiple environmental variables to examine the ecology, the diversity and the composition of planktonic microbial eukaryotes at the Eastern Mediterranean Sea, while trying to deepen the understanding of the relationship between plankton and nutrient supply. Initially, the composition and distribution of microbial plankton eukaryotes at the ultraoligotrophic Eastern Mediterranean open sea, was studied. Our results showed that microbial eukaryotic communities were structured according to seawater depth. In surface waters, different sites shared high percentages of molecular operational taxonomic units (MOTUs), but this was not the case for deep-sea communities. Plankton biomass, on the other hand, was significantly different among sites, implying that communities of a similar composition may not support the same activity or population size. Water temperature and dissolved organic matter were found to significantly affect community distribution. Micro-eukaryotic distribution was additionally affected by the nitrogen-to-phosphorus ratio (N/P) and viral abundance, while smaller-in-size communities were affected by zooplankton. Therefore, it is underlined that, even within restricted oceanic areas, marine plankton may follow distribution patterns that are largely controlled by environmental variables. External inputs into marine coastal ecosystems increase as a result of expanding human activities. Following the changes in the water column physiochemistry after land inputs, the planktonic community is affected. The second part of this work studied the structure and composition of planktonic eukaryotic communities from coastal areas of the Eastern Mediterranean. In particular, three coastal areas that receive high nutrient input from adjacent rivers and nearby agricultural activity were studied, in comparison to three areas that receive lower nutrient input and showed lower nutrient concentration in the water column. Dinoflagellata prevailed regardless of the nutrient disturbance, however, phylla as Bacillariophyta and Chlorophyta were more prominent in the most nutrient affected areas. Eukaryotic communities of the most affected areas were associated with variables such as chlorophyll, dissolved nitrogen and oxygen concentration and prey abundance; thus, the altered community composition of the affected areas was associated to resources availability and higher trophic status. To further study the ecological relationships created under the different enrichment conditions, coexistence networks of eukaryotic microorganisms were constructed. The ecological network of the areas receiving greater inputs from the land exhibited fewer species-to-species relationships, was less coherence and specific microorganisms were found to play a greater role. Overall, differences were found both in the ecological relationships and in the diversity and composition of the eukaryotic plankton community between areas that receive varying anthropogenic nutrient inputs. Finally, the effects of the abrupt input of high quantities of dissolved inorganic nitrogen and phosphorus were investigated in an attempt to simulate the nutrient disturbances caused by eutrophication and climate change. Two nutrient levels were created through the addition of different quantities of dissolved nutrients in a mesocosm experiment. During the developed blooms, compositional differences were found within bacteria and microbial eukaryotes, and communities progressed towards species of faster metabolisms. Regarding the different nutrient concentrations, different microbial species were associated with each nutrient treatment and community changes spanned from the phylum to the operational taxonomic unit (OTU) level. Network analyses revealed important differences in the biotic connections developed: more competitive relationships were established in the more intense nutrient disturbance and networks of contrasting complexity were formed around species of different ecological strategies. According to these results sudden disturbances in water column chemistry lead to the development of entirely different microbial food webs with distinct ecological characteristics. In conclusion, plankton biomass responds even in slight nutrient concentration changes, however, it seems that the composition of eukaryotic community responds only to intense nutrient level changes. The network analysis of plankton suggests that the overall changes of the water column system are highly depended to the relationships among microorganisms. Overall, this study gives fresh perspective to the ecological approach of plankton microbial eukaryotes in connection to the nutrient supply in the water column.
Language Greek, English
Subject Biomass
Marine environment
Network analyses
Ανάλυση δικτύων
Θαλάσσιο περιβάλλον
Issue date 2019-11-29
Collection   Faculty/Department--Faculty of Sciences and Engineering--Department of Biology--Doctoral theses
  Type of Work
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