Effects of increased atmospheric CO₂ on small and intermediate sized osmotrophs during a nutrient induced phytoplankton bloom

A. I. Paulino (1) , J. K. Egge (1) , A. Larsen (1)

1 Dept. of Biology

We report the transient population dynamic response of the osmotrophic community initiated by a nutrient pulse in mesocosms exposed to different pCO₂ levels as well as quantitative variations in phytoplankton and heterotrophic bacteria created by the difference in CO₂ exposure. Coastal seawater was enclosed in floating mesocosms (27 m³) and nutrients were supplied initially in order to stimulate growth of microbial organisms, including the coccolitophorid Emiliania huxleyi. The mesocosms were modified to achieve 350 ?atm (1×CO₂), 700 ?atm (2×CO₂) and 1050 µatm (3×CO₂) CO₂ pressure. The temporal dynamics was related to the nutrient conditions in the enclosures. Numerically small osmotrophs (picoeukaryotes and Synechoccocus sp.) dominated initially and towards the end of the experiment, whereas intermediate sized osmotrophs bloomed as the initial bloom of small sized osmotrophs ceased. Maximum concentrations of E. huxleyi were approximately 4.6×10³ cells ml^?1 whereas other intermediate sized osmotrophs reached approximately twice as high concentrations. Osmotrophic succession pattern did not change, and we were not able to detect differences with regard to presence or absence of specific osmotrophic taxa as a consequence of altered atmospheric CO₂ concentration. Quantitative effects on the microbial communities associated with the CO₂ treatment were, however, observed towards the end of the experiment.

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Astrophysique [astro-ph]; Interfaces continentales, environnement; Océan, Atmosphère; Sciences de la Terre

A. I. Paulino, J. K. Egge, A. Larsen. Effects of increased atmospheric CO₂ on small and intermediate sized osmotrophs during a nutrient induced phytoplankton bloom. Biogeosciences Discussions, 2007, 4 (6), pp.4173-4195. ⟨hal-00297940⟩