| Summary: | This doctoral thesis aimed at the establishment of molecular tools (ARISA and 454-pyrosequencing) for protist diversity assessments in polar regions and at the application of these tools for studying protist diversity in the Fram Strait and in the Central Arctic Ocean. In this thesis, three hypotheses were put forward: i) Molecular surveys of genetic protist diversity, obtained by 454-pyrosequencing, constitute an adequate tool for assessing natural protist diversity ii) Water masses in the Arctic Ocean and in the Fram Strait are characterized by distinct protist communities and iii) Complex hydrographical and environmental situations can be evaluated via genetic information. A comprehensive study of protist diversity is required, because so far investigations were biased towards big size cells (≥2 µm). A correct identification of smaller cells is almost impossible due to the small size and lack of morphological markers. However, a proper survey of protist diversity demands the inclusion of all size classes. This is of particular relevance, considering the fact that small cells were observed to dominate protist assemblages at certain times, according to abiotic circumstances. The Arctic Ocean constitutes in two ways an important research area: on the one hand, it experiences intense variations in the light regime based on seasonality and sea ice; and on the other hand, it is assumed to be affected more severely by climate change than other world oceans. Since marine microorganisms are highly responsive to environmental forcing, changes will likely impact the protist community structures. Against the background of ongoing environmental changes in the Arctic, a study of protist diversity is further crucial in order to get a baseline for the assessment of future community structure changes. i) The assay of the 454-pyrosequencing suitability was carried out by using different wide-employed methods for reconciliation, sharing the same (clone library and ARISA) and different drawbacks (light microscopy and HPLC). The ...
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