During the project we have:
1. Conducted a large scale collaborative study to investigate the adaptation of the cosmopolitan diatom species 'Skeletonema marinoi' to dynamic nutrient conditions. More specifically, we have examined how this affects the production of transparent exopolymeric particles (TEP) and the formation of aggregates, whilst our collaborators focused on examining carbon and nitrate assimilation processes. The analysis of TEP samples from both experiments is in progress and intended for publication. The researcher is co-author on the study of carbon and nitrate assimilation published in Environmental Biology (
https://doi.org/10.1111/1462-2920.14434(s’ouvre dans une nouvelle fenêtre)) which revealed a high diversity of nutrient demand not only at a clone-specific level but also at the single-cell level allowing the population to sustain itself and adapt to dynamic nutrient conditions.
2. Investigated the effect of signaling molecules (copepodamides) produced by copepods on the production of TEP and aggregate formation of Skeletonema marinoi. Two experiments were run as well as two preliminary experiments with data analysis in progress of all TEP and aggregate measurements. First indications of the data analysis reveal effects of the copepodamides on aggregate size, and sinking velocity as well as associated TEP content. A manuscript outline has been prepared and an abstract submitted for results to be presented in May 2019 at the “Marine Particles and Phycospheres” conference in Ascona, Switzerland.
3. Examined flow field data measured around permeable and impermeable aggregates in detail. Results indicate that highly irregularly shaped permeable aggregates formed from the diatom Chaetoceros affinis behaved similarly to more compact spherical aggregates formed by Skeletonema marinoi as well as impermeable model aggregates. The presence of TEP dominated the interstitial spaces of Chaetoceros aggregates compared to the cell-to-cell stickiness found in Skeletonema aggregates. Subsequently, the transport of gases, nutrients, and solutes occurs by diffusion even within large, apparently porous diatom aggregates during sinking. Results from this were presented at the Gordon Research Conference “The Biologically-Driven Ocean Carbon Pumps” in June 2016 as well as at the EuroMarine Foresight Symposium in October 2016: “The Biological Carbon Pump in a Changing World” which was co-organized by the researcher. The final manuscript is currently being assembled.
4. Set up digital holographic microscopy imaging capabilities at UGOT and used this to explore the structure of aggregates and the presence of TEP within. Access to an oLine D3HM (Ovizio Imaging Systems, Belgium) were provided via Prof. Filip Meysman of the partner organization, whilst a QMod module (Ovizio Imaging Systems, Belgium) for UGOT microscope facilities was obtained via Swedish funding. All experiments benefitted from the access to these facilities. In addition, we investigated embedded natural aggregates through collaborative efforts with Dr. Morten Iversen’s lab in Germany (Marum) which will require further study.
5. Described particle sources and transport in stratified Nordic coastal seas in the Anthropocene in a review initiated as a departmental effort at UGOT. We highlighted the particular importance of particles in stratified coastal waters and estuaries, their roles in natu¬ral processes, their formation and transport (including aggregation processes), and their interactions with anthropogenic activities. E. Zetsche coordinated the contribution which has been published in Elementa Science of the Anthropocene (
https://doi.org/10.1525/elementa.149(s’ouvre dans une nouvelle fenêtre)).
To date, results from this project were presented at one international conference and one workshop, which was also co-organized by the researcher. A third presentation is scheduled for May 2019. The initially planned attendance of a second international conference, where a session was also co-organized was cancelled due to the advanced stage of the researcher’s pregnancy at the time. Two manuscripts have been published and two are in preparation. We expect at least one other manuscript to be generated from this work making a minimum total of five. E. Zetsche also presented her expertise and knowledge on digital holographic microscopy to the Scandinavian research community in an oral presentation at a locally hosted conference dedicated to imaging techniques and has established the technique at the Department of Marine Sciences.
