Over-calcified forms of the coccolithophore Emiliania huxley in high-CO2 waters are not preadapted to ocean acidification

• Published in: Biogeosciences
• Main Authors: Mella-Flores, Daniella, Gaitán-Espitia, Juan Diego, Mahdi Bendif, El, DÍaz-Rosas, Francisco, Von Dassow, Peter, Torres, Rodrigo, Rokitta, Sebastian, John, Uwe
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2018
• Subjects: Huxley; Pacific; Ocean acidification
• Online Access: https://doi.org/10.5194/bg-15-1515-2018; http://hdl.handle.net/10722/253187

© Author(s) 2018. Marine multicellular organisms inhabiting waters with natural high fluctuations in pH appear more tolerant to acidification than conspecifics occurring in nearby stable waters, suggesting that environments of fluctuating pH hold genetic reservoirs for adaptation of key groups to ocean acidification (OA). The abundant and cosmopolitan calcifying phytoplankton Emiliania huxley exhibits a range of morphotypes with varying degrees of coccolith mineralization. We show that E. huxley populations in the naturally acidified upwelling waters of the eastern South Pacific, where pH drops below 7.8 as is predicted for the global surface ocean by the year 2100, are dominated by exceptionally over-calcified morphotypes whose distal coccolith shield can be almost solid calcite. Shifts in morphotype composition of E. huxley populations correlate with changes in carbonate system parameters. We tested if these correlations indicate that the hyper-calcified morphotype is adapted to OA. In experimental exposures to present-day vs. future pCO2 (400 vs. 1200 μatm), the over-calcified morphotypes showed the same growth inhibition (g-29.1±6.3 %) as moderately calcified morphotypes isolated from non-acidified water (g-30.7±8.8 %). Under the high-CO2-low-pH condition, production rates of particulate organic carbon (POC) increased, while production rates of particulate inorganic carbon (PIC) were maintained or decreased slightly (but not significantly), leading to lowered PIC / POC ratios in all strains. There were no consistent correlations of response intensity with strain origin. The high-CO2-low-pH condition affected coccolith morphology equally or more strongly in over-calcified strains compared to moderately calcified strains. High-CO2-low-pH conditions appear not to directly select for exceptionally over-calcified morphotypes over other morphotypes, but perhaps indirectly by ecologically correlated factors. More generally, these results suggest that oceanic planktonic microorganisms, despite their rapid turnover ...