Abstract
Summary Coccolithophores are globally distributed unicellular marine algae that are characterized by their covering of calcite coccoliths. Calcification by coccolithophores contributes significantly to global biogeochemical cycles. However, the physiological requirement for calcification remains poorly understood as non‐calcifying strains of some commonly used model species, such as Emiliania huxleyi, grow normally in laboratory culture.To determine whether the requirement for calcification differs between coccolithophore species, we utilized multiple independent methodologies to disrupt calcification in two important species of coccolithophore: E. huxleyi and Coccolithus braarudii. We investigated their physiological response and used time‐lapse imaging to visualize the processes of calcification and cell division in individual cells.Disruption of calcification resulted in major growth defects in C. braarudii, but not in E. huxleyi. We found no evidence that calcification supports photosynthesis in C. braarudii, but showed that an inability to maintain an intact coccosphere results in cell cycle arrest.We found that C. braarudii is very different from E. huxleyi as it exhibits an obligate requirement for calcification. The identification of a growth defect in C. braarudii resulting from disruption of the coccosphere may be important in considering their response to future changes in ocean carbonate chemistry.
Highlights
Coccolithophores (Calcihaptophycidae) are globally abundant, single-celled marine phytoplankton characterized by the production of elaborate calcite platelets
We examined the physiological effects of disrupting calcification in E. huxleyi and C. braarudii using multiple independent methodologies: low-Ca2+ seawater, the addition of HEDP or the addition of Ge
Ge was not applied to E. huxleyi, as we have demonstrated previously that this species does not require Si for calcification and is unaffected by Ge, even at very high Ge/Si ratios (Durak et al, 2016)
Summary
Coccolithophores (Calcihaptophycidae) are globally abundant, single-celled marine phytoplankton characterized by the production of elaborate calcite platelets (coccoliths). These are produced in an intracellular compartment (coccolith vesicle) and secreted to the cell surface, where they are arranged extracellularly to form a coccosphere (Brownlee & Taylor, 2003; Marsh, 2003; Taylor et al, 2017). Calcification by coccolithophores contributes to a rain of calcite from surface waters to depth, which can remineralize and contribute to a vertical alkalinity gradient in the water column (Milliman, 1993) or form vast sedimentary deposits on the ocean floor (Thierstein et al, 1977). Coccolithophores are crucial contributors to ocean biogeochemical cycles and much research has focused on how calcification may be impacted by future changes in ocean carbonate chemistry (Riebesell et al, 2000; Rost & Riebesell, 2004; Ridgwell et al, 2009; Meyer & Riebesell, 2015)
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