Thiamine dynamics in the pelagic food web of the Baltic Sea

Thiamine (vitamin B1) is involved in several basal metabolic processes. It is an essential compound for many organisms and in aquatic systems it is mainly produced by phytoplankton and prokaryotes and transferred to higher trophic levels through grazing and predation. The occurrence of thiamine deficiency in top predators has been reported from several aquatic systems. In the Baltic populations of the Atlantic salmon (Salmo salar) this has been observed since 1974 and recently thiamine deficiency has also been reported for Baltic sea birds. This thesis aims at investigating what processes that governs the flow of thiamine from the primary producers to top predators via zooplankton grazers and planktivoric fish. Paper I showed that abiotic stress factors such as salinity, temperature and light conditions can alter the thiamine content of phytoplankton. Paper II showed that abiotic factors indirectly can affect the stress resistance of zooplankton grazers by changing the nutritional quality of their food. In Paper III we found that the in situ thiamine content of zooplankton grazers was directly affected by that of the phytoplankton diet. In Paper IV we found a similar connection between the thiamine contents of Baltic salmon and herring, one of the major salmon prey species. In Paper V we looked at the thiamine content of the pelagic food web of the Baltic Sea as a whole and found a pattern of trophic dilution; the higher the trophic level of an organism (i.e. the further away from the source of thiamine in the food web), the lower was its thiamine content. In all, the results of this thesis suggests a bottom up effect on the thiamine status of the higher trophic levels of  the Baltic Sea and that external factors, both natural and man-made, have the capability to affect the thiamine status of the plankton communities and thereby the whole Baltic ecosystem. Thiamine and other micronutrients are not something generally considered in the environmental management of aquatic systems but the results of this thesis suggest that ecological disturbances indirectly can have negative effects on top predators via a disrupted supply of essential substances.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript.</p

Bacterial community structure in a sympagic habitat expanding with global warming: brackish ice brine at 85–90 °N

© 2018, International Society for Microbial Ecology.Larger volumes of sea ice have been thawing in the Central Arctic Ocean (CAO) during the last decades than during the past 800,000 years. Brackish brine (fed by meltwater inside the ice) is an expanding sympagic habitat in summer all over the CAO. We report for the first time the structure of bacterial communities in this brine. They are composed of psychrophilic extremophiles, many of them related to phylotypes known from Arctic and Antarctic regions. Community structure displayed strong habitat segregation between brackish ice brine (IB; salinity 2.4–9.6) and immediate sub-ice seawater (SW; salinity 33.3–34.9), expressed at all taxonomic levels (class to genus), by dominant phylotypes as well as by the rare biosphere, and with specialists dominating IB and generalists SW. The dominant phylotypes in IB were related to Candidatus Aquiluna and Flavobacterium, those in SW to Balneatrix and ZD0405, and those shared between the habitats