AUTHOR=Schulz Kai G. , Bach Lennart T. , Bellerby Richard G. J. , Bermúdez Rafael , Büdenbender Jan , Boxhammer Tim , Czerny Jan , Engel Anja , Ludwig Andrea , Meyerhöfer Michael , Larsen Aud , Paul Allanah J. , Sswat Michael , Riebesell Ulf 

TITLE=Phytoplankton Blooms at Increasing Levels of Atmospheric Carbon Dioxide: Experimental Evidence for Negative Effects on Prymnesiophytes and Positive on Small Picoeukaryotes

JOURNAL=Frontiers in Marine Science

VOLUME=4

YEAR=2017

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2017.00064

DOI=10.3389/fmars.2017.00064

ISSN=2296-7745

ABSTRACT=<p>Anthropogenic emissions of carbon dioxide (CO<sub>2</sub>) and the ongoing accumulation in the surface ocean together with concomitantly decreasing pH and calcium carbonate saturation states have the potential to impact phytoplankton community composition and therefore biogeochemical element cycling on a global scale. Here we report on a recent mesocosm CO<sub>2</sub> perturbation study (Raunefjorden, Norway), with a focus on organic matter and phytoplankton dynamics. Cell numbers of three phytoplankton groups were particularly affected by increasing levels of seawater CO<sub>2</sub> throughout the entire experiment, with the cyanobacterium <italic>Synechococcus</italic> and picoeukaryotes (prasinophytes) profiting, and the coccolithophore <italic>Emiliania huxleyi</italic> (prymnesiophyte) being negatively impacted. Combining these results with other phytoplankton community CO<sub>2</sub> experiments into a data-set of global coverage suggests that, whenever CO<sub>2</sub> effects are found, prymnesiophyte (especially coccolithophore) abundances are negatively affected, while the opposite holds true for small picoeukaryotes belonging to the class of prasinophytes, or the division of chlorophytes in general. Future reductions in calcium carbonate-producing coccolithophores, providing ballast which accelerates the sinking of particulate organic matter, together with increases in picoeukaryotes, an important component of the microbial loop in the euphotic zone, have the potential to impact marine export production, with feedbacks to Earth's climate system.</p>