Long-term adaptation of the coccolithophore Emiliania huxleyi to ocean acidification and global warming
This Thesis summarizes the adaptive effects of ocean acidification and global warm on the coccolithophore Emiliania huxleyi. The adaptive effects were experimentally assessed in a long term evolutionary experiment. After 2100 asexual generations of selection to CO2 the fitness (growth rate) increased slightly over time under 1100 µatm pCO2. Under 2200 µatm pCO2 the fitness advantage of 5% at 500 generations remained unchanged. The phenotypic trait of calcification was partly restored within 500 generations. Thereafter, calcification was reduced in response to selection. The reduction of calcification was not constitutively, as the calcite per cell quotas were restored when assessed with 400 µatm pCO2. Temperature adaptation occurred independently of ocean acidification levels. The fitness increase in growth rate due was up to 16% in populations adapted to high temperature and high CO2 compared to not adapted cells under selection conditions. The ratio of particular inorganic (PIC) and organic carbon (PIC:POC) recovered to their initial ratio after temperature adaptation, even under elevated CO2. Cells evolved to a smaller size accompanied by a reduction in POC-content. Production rates were restored to values under present-day ocean conditions, owing to adaptive evolution in growth rate. Temperature adaptation increased the effect on persisting CO2 adaptation in growth rate. The immediate physiological effect on PIC per cell was diminished compared to the lower temperature treatment, and so were the adaptive effects. Temperature adaptation reduced the negative effects of ocean acidification. Both adaptations were necessary to receive the full fitness effect under high-temperature-high-CO2-conditions. As consequence both adaptive effects are additive. Global warming may reduce the adverse effects of ocean acidification on E. huxleyi populations. My results show further, that marine phytoplankton may evolve changes in the plastic response under future ocean conditions.
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