95. Growth response of calcifying and non-calcifying phytoplankton to changes in seawater carbonate speciation and divalent cation concentration

Marina T Botana (1) and Marius N Müller (2)

1, 2 Instituto Oceanográfico – Universidade de São Paulo, São Paulo, SP, 05508-120, Brazil

Phytoplankton has a major contribution to the oceans “organic carbon pump” due to the fixation of CO2 and its transport to deep waters. Besides the organic contribution, calcifying species, such as coccolithophores, play a unique role to the calcite production and its presence in the geological record. Recently, phytoplankton calcification has been described to alleviate cellular Ca poisoning at high seawater Ca concentrations [1] (e.g. Cretaceous). Presumably, high cytosol Ca concentrations interfere with cellular Mg biochemistry resulting in reduced phytoplankton growth. In this project we address two fundamental questions regarding the mechanism of Ca-detoxification via calcification. (1) Is Ca-poisoning aggravated at low pH conditions in calcifying compared to non-calcifying phytoplankton? (2) Is the intensity of Ca-poisoning influenced by seawater Mg concentrations? In controlled laboratory experiments, three calcifying (E. huxleyi, G. oceanica and P. carterae) and two non-calcifying species (I. galbana and D. salina) are grown under gradual changes of seawater carbonate chemistry (pH, DIC, pCO2), Ca and Mg concentrations. These experiments and their results will have implications on the function of calcification in phytoplankton and their evolutionary trajectory in regard to changing seawater chemistry.

[1] Müller, M. N. et al. Phytoplankton calcification as an effective mechanism to prevent cellular calcium poisoning, Biogeosciences Discuss., 12, 12691-12712, doi:10.5194/bgd-12-12691-2015, 2015.