Award: OCE-1538602

Collaborative Research: Effects of multiple stressors on Marine Phytoplankton Overall Goal: This research investigated the acclimatization response of phytoplankton to different, simultaneous environmental stressors. Each phytoplankton species has the capability to acclimatize within a finite range to changes in temperature, light, pCO2 and nutrient availability. However, the response of phytoplankton to multiple simultaneous stressors is frequently complex, because of interactive effects in the physiological response. Together with our collaborator, we experimentally investigated the combined influences of changes in pCO2, temperature, light, and nitrate availability on phytoplankton growth using different phytoplankton cultures. Our part of the project focused on growth and photophysiological responses to changes in pCO2, temperature, light, whereas our collaborators focused on the effects of nutrient limitation during changing temperature, light or pCO2 conditions. Significance: Increasing atmospheric pCO2 leads to changes in all the environmental conditions important for phytoplankton success: Direct effects include an increase in temperature and pCO2 in the surface ocean; the stronger vertical temperature gradient will lead to changes in nutrient and light availability. As the growth success of a phytoplankton species is in part, driven by these environmental conditions, changes in phytoplankton composition and productivity are expected. Such potential changes have important implications, because phytoplankton play a key role in marine systems, determining for example fisheries yield and the carbon sequestration capability of the ocean. However, the capacity of phytoplankton to acclimatize to simultaneous changes in several environmental parameters is largely unexplored and predictive models lack data on interactive effects of multiple stressors on phytoplankton. Our data will provide the input to create such models. Broader Impacts: The experiments represent a case study on the complex and interactive effects of growth conditions on organisms. In a world that is getting more and more complex, the understanding of the complexity of biological interactions is important for future voters and residents alike. This case study can be used for teaching on all levels: (i) Young scientists and researchers can benefit from the support decision tool and training aids developed within the SCOR working group on Changing Oceans Biological Systems (COBS; https://scor149-ocean.com/decision-support-tool). (ii) Students working in our lab or attending our lectures benefited by learning specific oceanographic techniques, or scientific hypothesis testing, even conducting their own project and gaining a degree. (iii) Our participation in teacher training program means that high school students benefit from the new teaching unit developed based on the teachers 6 week participation in our lab. (iv) The comic story developed together with comic artist A. Warner introduces a larger and more diverse audience to the problems of multiple simultaneous stressors (https://www.mun.ca/osc/upassow/PhytoplanktonStressors.pdf). (v) This data set will contribute towards the construction of models that can predict responses of the ocean to climate change, e.g. the consequences for fisheries or carbon sequestration. Predictions will allow the development of societal and regulatory response and mediating measures. Summary of Experiments: Five experimental series, each with one species, were conducted. Each series required many treatments (e.g. 8 irradiances * 6 temperatures = 48 treatments). Each experiment consisted of an acclimatization phase and an experimental phase and lasted for days to weeks. Each series required several pre-tests to determine growth ranges and approaches for the specific species. Two-stressor (temperature and irradiance) effects on Tp-1335 (Thalassiosira pseudonana CCMP 1335), which was a master thesis for one student and will provide input to a comparison, see #2. Two-stressor (temperature and irradiance) effects on Tp-1014 (Thalassiosira pseudonana CCMP 1014), which was compared with the above-mentioned strain and also constituted a master thesis for one student. Each of these first two series gave several undergraduates the opportunity to earn some money and to learn a specific analysis technique. Three stressor (temperature, irradiance, pCO2) effects on Tp-1014, using insights from the previous experiment to keep the number of treatments manageable in a three stressor set-up. This and the next series gave several undergraduate students the opportunity to participate and learn about complex experimental design, as well as providing a job and training for a lab assistant. The project scientist had the opportunity to advance his scientific career, as well as learning to mentor students. Three stressor (temperature, irradiance, pCO2) effects on Synechococcus elongatus CCMP 1629 provide an example of a completely different (unrelated) taxa of phytoplankton (prokaryotes vs. eukaryotes). A comparison will give insights on the general applicability of data collected. Two-stressor (pCO2, temperature) effects on a local strain of E. huxleyi (cocolithophore, isolated from the Santa Barbara Channel). This was an undergraduate honors project, for which the student was awarded independent support from the Coastal Fund at UCSB. This species of phytoplankton is also completely different from the above two. All data was submitted to the public database BCO-DMO and scientific publications are in different stages of completion. Additionally we were involved in the research led by our collaborators. Last Modified: 08/07/2020 Submitted by: Uta D E Passow