Abstract. Compared to the rest of the globe, the Arctic Ocean is affected
disproportionately by climate change. Despite these fast environmental
changes, we currently know little about the effects of ocean acidification
(OA) on marine key species in this area. Moreover, the existing studies
typically test the effects of OA under constant, hence artificial, light
fields. In this study, the abundant Arctic picoeukaryote Micromonas pusilla was acclimated to
current (400 µatm) and future (1000 µatm) pCO2 levels under a
constant as well as a dynamic light, simulating more realistic light fields as
experienced in the upper mixed layer. To describe and understand the
responses to these drivers, growth, particulate organic carbon (POC)
production, elemental composition, photophysiology and reactive oxygen
species (ROS) production were analysed. M. pusilla was able to benefit from OA on
various scales, ranging from an increase in growth rates to enhanced
photosynthetic capacity, irrespective of the light regime. These beneficial
effects were, however, not reflected in the POC production rates, which can
be explained by energy partitioning towards cell division rather than
biomass build-up. In the dynamic light regime, M. pusilla was able to optimize its
photophysiology for effective light usage during both low- and high-light
periods. This photoacclimative response, which was achieved by modifications
to photosystem II (PSII), imposed high metabolic costs leading to a
reduction in growth and POC production rates when compared to constant
light. There were no significant interactions observed between dynamic light
and OA, indicating that M. pusilla is able to maintain effective photoacclimation
without increased photoinactivation under high pCO2. Based on these
findings, M. pusilla is likely to cope well with future conditions in the Arctic
Ocean.
Supplementary material to "The Arctic picoeukaryote <i>Micromonas pusilla</i> benefits from Ocean Acidification under constant and dynamic light"
