Kalter, Verena (2017) Influence of ocean acidification on a natural plankton community during the post-bloom phase – a mesocosm study in a Norwegian fjord. (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 40 pp.

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Abstract

In this large-scale in-situ mesocosm study, phytoplankton community and biogeochemical responses to ocean acidification were tested. Contrary to most other such studies, no nutrients were added to initiate a phytoplankton bloom. Instead, responses in the nutrient-deplete postbloom phase were monitored for 2 months. At the beginning of May 2015, 8 mesocosms were deployed in the Raunefjord near Bergen, Norway. CO2 was added to 4 mesocosms to reach target values of ~2200 μatm. The pCO2 of the remaining 4 mesocosms was left unchanged and served as ambient (~400 μatm) control. Phytoplankton community and biogeochemical responses showed clear differences between treatments. Those differences were visible in distinct phases of the experiment, or diverged more strongly with ongoing decline of the bloom. Phytoplankton community composition affected the development of particulate matter in both treatments. Furthermore, results hint at faster export of particulate material at high CO2. Direct effects of ocean acidification on primary producers and consequent particulate matter dynamics are evident, but grazing also played an important role in this study. Hence, the knowledge gained from this experiment could help to better understand future responses of pelagic ecosystems with complex organism interactions.

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