Multi‐trait responses in two marine diatoms to pH and irradiance reveal interactive effect of light and acidification, mediated by silicification

Abstract

Ocean ecosystem shifts in response to anthropogenic climate change are impacting marine organisms, including phytoplankton. Ocean acidification and warming represent two key threats to marine phytoplankton, causing significant changes to the upper mixed layer of the ocean, reshuffling their distribution, and reorganizing their physiology and metabolism. In this study, we investigated changes in biomolecular composition and silicification rates of the two “model” diatom species Phaeodactylum tricornutum and Thalassiosira weissflogii under low (~ 350) and projected future (~ 800) p CO 2 concentrations with low (20 μ mol photons m −2 s −1 ) and high (200 μ mol photons m −2 s −1 ) light, simulating expected climate change‐induced impacts of ocean shoaling and acidification. Specifically, our study conditions elicited changes in lipid and protein content in both species. We also found a negative effect of p CO 2 on silica production under high light in T. weissflogii that was linked to improved photochemical efficiency. This interactive effect between light and p CO 2 with silica production suggests a potential controlling role of the frustule in diatom photosynthesis and photoprotection (energy balance). Based on these data, ocean shoaling and acidification have the potential to influence the nutritional value and biogeochemical role of diatoms through its effect on diatom frustule synthesis and photobiology.

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