The physiological response of the Arctic haptophyte Phaeocystis pouchetii to marine heatwaves

• Main Author: Urbschat, Naomi
• Other Authors: Rost, Björn, Bischof, Kai
• Format: Thesis
• Language: unknown
• Published: 2022
• Subjects: Arctic; Arctic Ocean; Global warming; Phytoplankton
• Online Access: https://epic.awi.de/id/eprint/57572/; https://epic.awi.de/id/eprint/57572/1/MScThesis_Naomi%20Urbschat.pdf; https://hdl.handle.net/10013/epic.1ecbb7b8-b029-4a5c-9da2-59a4d04a14b9

Due to the ongoing global warming extreme weather events like marine heatwaves (MHWs) have already become more frequent and intense as well as longer lasting, and their probability of occurrence is projected to increase in the future, especially in the Arctic Ocean. MHWs can rapidly push a species beyond their usually experienced temperature range, often exceeding physiological tolerance thresholds. Furthermore, fluctuation between higher and lower temperatures associated with MHWs can induce metabolic mismatches between physiological subprocesses. Thus, MHWs could have worse effects on the performance of a species than those emanating from the mean temperature rise due to global warming. Despite this potential threat, knowledge on the impact of MHWs on Arctic phytoplankton is still scarce. In this master thesis project, I designed a laboratory experiment to investigate the physiological capacity of the Arctic key phytoplankton species Phaeocystis pouchetii to physiologically acclimate to heatwave scenarios. After pre-acclimation to experimental conditions at 3 °C, cells were rapidly exposed to two MHWs with an intensity of 6 °C for varying durations (MHW1: 6 days, MHW2: 10 days), followed by a 5-day recovery phase at 3 °C. The non-acclimated response to the MHW treatments was further compared to the acclimated response of cells experiencing continuous heat exposure of 6 °C for 3 weeks. The physiological performance of cells was investigated by assessing specific growth rates, elemental composition and cellular chlorophyll a content. Furthermore, photophysiology was assessed by fast repetition rate fluorometry (FRRF) measurements of variable chlorophyll fluorescence and intracellular levels of O2•- and H2O2 were determined by flow cytometric analysis. The results demonstrated that warming strongly stimulated growth rates in the short-term and reduced photosynthetic efficiency and triggered production of reactive oxygen species (ROS) in the long-term. Intracellular ROS levels reached a maximum after 6 days and ...