Description: Sea ice is a large environment controlled by a number of abiotic factors (i.e. low temperatures and high salinities). Despite these harsh conditions, it is inhabited by a diverse community and significantly contributing to primary production in ice-covered regions. While this biodiversity has been investigated in the past by classical methods, little is known about its functional biodiversity, i.e. which species are actively contributing with which functions to the community. By sequencing 18S rRNA and rDNA amplicons, we were able to compare the “total” biodiversity (rDNA-based) with the “active” biodiversity (rRNA-based) and found an over-representation of certain groups (i.e. Bacillariophyceae and Ciliophora) in the active part of the community. Furthermore, we were able to isolate an abundant naviculoid sea ice diatom member (CCMP2297) of the Arctic sea ice community and conducted temperature stress experiments (10 °C, 5 °C, -2 °C, -5 °C) and analyzed not only physiological responses to high and cold temperature stress, but also the molecular responses to thermal stress by sequencing the transcriptome. We found that based on physiological parameters this diatom has a broad thermal range (5 °C to -5 °C) but significantly changes its gene expression pattern at higher temperatures.

Description: Sea ice is a large and diverse ecosystem inhabited by bacteria and protists contributing significantly to primary production in ice-covered regions. In the Arctic Ocean, sea ice consists of mixed multi-year ice (MYI) and thinner first-year ice (FYI). Due to global warming we experience a shift from MYI towards FYI. Despite the great importance of the sea ice ecosystem, little is known about its functional biodiversity, i.e. which species are actively contributing with which functions to the community. We investigated the eukaryotic biodiversity in MYI and FYI from the central Arctic Ocean using 18S rRNA and rDNA amplicons and compared the “total” biodiversity (rDNA-based) with the “active” biodiversity (rRNA-based). Groups like Ciliophora, Bicosoecida and Bacillariophyceae were over-represented in the active part of the community and grazers appear most active in one FYI station due to the advanced stage of melt compared to the other stations. Furthermore, preliminary results of transcriptomic stress experiments with an abundant naviculoid sea ice diatom show that based on physiological parameters this diatom has a broad thermal range (5 °C to -5 °C) but significantly changes its gene expression pattern at higher temperatures.

Description: The effect of increased CO2 concentration on the green, Ulva lactuca, Acrosiphonia arcta, and A. sonderii, and the brown, Laminaria digitata, Saccharina latissima and Pylaiella littoris, seaweeds was investigated in the laboratory. We designed to aerate algal discs of sheet-like Ulva, filaments of Acrospihonia and Pylaiella and young sporophytes of thick-blade kelps in 1L bottles with pre-industrial (280 ppm), ambient (≈ 380 ppm), and elevated (700 ppm) carbon dioxide for 15 days under 15°C and saturating photosynthetically active radiation (PAR). Routine measurements of CO2 using LICOR gas analyser showed the concentration in compressed ambient air was severely reduced down to 160 ppm effectively altering our desired experimental treatment to the lower spectrum compared to the pre-mixed bottled CO2. Water chemistry showed our CO2 concentrations were negatively correlated with pH and dissolved CO3, and positively correlated with dissolved CO2, and HCO3. Increasing CO2 concentration and consequent acidification was observed to exhibit no significant effect on photosynthesis and growth of all algae examined except for the higher growth rate in U. lactuca under 700 ppm compared to 160 ppm. In retrospect, our 160 ppm treatment may have no ecological significance relative to pre-industrial and the climate change-projected increase in CO2 concentration but showed the ability of some non-calcareous seaweed to cope up with extremely low and high CO2 concentrations to support photosynthesis and growth; an indication of a possible induction and suppression of carbon-concentrating mechanism at low and high CO2 concentrations, respectively, without extra energetic cost in most of the macroalgae investigated.

Description: Marine macroalgae are important components of coastal ecosystems, providing food and habitat for numerous species. Since the atmospheric CO2 concentration increases, the CO2 concentration of the upper surface layers of the global oceans increases as well, causing an alteration of the seawater chemistry. This shift can affect marine macroalgae which depend on carbon to efficiently run photosynthesis. Thus, the performance of marine macroalgae might be influenced by ocean acidification with as yet unpredictable consequences for the entire ecosystem. Intertidal macroalgae are not only affected by enhanced atmospheric CO2 concentrations but also by severe alterations in their abiotic environment due to the diurnal tidal cycle (e.g. tidal emergence). This study aimed to provide the first data on the combined effects of enhanced CO2 and tidal emergence on the physiological performance and the expression of specific enzymes involved in carbon fixation in the common intertidal brown macroalga Fucus serratus. Furthermore, the applicability of molecular tools for this macroalgal species should be tested. F. serratus was cultured for two weeks at two different CO2 concentrations (280 and 1200 ppm) and two different tidal regimes (regular emergence and permanent submersion). Physiological traits were unaffected by enhanced CO2 concentrations and tidal emergence. Photosynthesis, growth and chlorophyll a content remained constant in each of the tested treatments. The insensitivity of physiological traits might be the result of an actively running carbon concentrating mechanism (CCM). By this CCM, photosynthesis of F. serratus is already carbon saturated at present CO2 concentrations. Gene expression analysis was performed by a quantitative real-time polymerase chain reaction (qRT-PCR), investigating the expression of genes encoding for carbonic anhydrase (CA), ribulose-1,5-bisphosphate carboxylase oxygenase (RubisCO) and phosphoenolpyruvate carboxykinase (PEPCK). Enhanced CO2 and tidal emergence did not affect the expression of the tested genes. The combination of both parameters led, however, to an up-regulation of all tested genes. Gene expression was unaffected by either CO2 or desiccation what might be due to the activity of the CCM. The up-regulation of the genes under the combined influence of the two factors cannot be explained by the present study. However, this study proved that (1) molecular tools are applicable to F. serratus and (2) that the two tested abiotic parameters interact, leading to a change in the transcriptional abundance of the tested enzymes. Although gene expression was affected by the interaction of the abiotic parameters, physiological traits remained unchanged, indicating that F. serratus is well adapted to its abiotic environments by a dynamical reaction without a change in fitness. The present study did not investigate enzyme activity and content. Future investigations should consider proteomic analysis to explain the effects of changing environments and different abiotic stresses in a more comprehensive way.