Niche partitioning by photosynthetic plankton as a driver of CO2-fixation across the oligotrophic South Pacific Subtropical Ocean

Julia Duerschlag, Wiebke Mohr, Timothy G. Ferdelman, Julie LaRoche, Dhwani K. Desai, Peter L. Croot, Daniela Voß, Oliver Zielinski, Gaute Lavik, Sten Littmann, Clara Martínez-Pérez, Bernhard Tschitschko (+4 others)
Oligotrophic ocean gyre ecosystems may be expanding due to rising global temperatures [1] [2] [3] [4] [5] . Models predicting carbon flow through these changing ecosystems require accurate descriptions of phytoplankton communities and their metabolic activities [6] . We therefore measured distributions and activities of cyanobacteria and small photosynthetic eukaryotes throughout the euphotic zone on a zonal transect through the South Pacific Ocean, focusing on the ultraoligotrophic waters of
more » ... e South Pacific Gyre (SPG). Bulk rates of CO 2 fixation were low (0.1 µmol C l −1 d −1 ) but pervasive throughout both the surface mixed-layer (upper 150 m), as well as the deep chlorophyll a maximum of the core SPG. Chloroplast 16S rRNA metabarcoding, and single-cell 13 CO 2 uptake experiments demonstrated niche differentiation among the small eukaryotes and picocyanobacteria. Prochlorococcus abundances, activity, and growth were more closely associated with the rims of the gyre. Small, fast-growing, photosynthetic eukaryotes, likely related to the Pelagophyceae, characterized the deep chlorophyll a maximum. In contrast, a slower growing population of photosynthetic eukaryotes, likely comprised of Dictyochophyceae and Chrysophyceae, dominated the mixed layer that contributed 65-88% of the areal CO 2 fixation within the core SPG. Small photosynthetic eukaryotes may thus play an underappreciated role in CO 2 fixation in the surface mixed-layer waters of ultraoligotrophic ecosystems.
doi:10.3929/ethz-b-000529368 fatcat:sn77vcaclvf6zifvemd7z3f7wu