On four occasions during the two year incubation of a subantarctic E. huxleyi culture (2015-11-20 to 2017-12-01), from Day 309 onwards, cell size of the cultures was measured at cross-over points, after 7 – 8 generations while still in exponential growth phase. Cells from Now (11°C and pH 8.1) and Future (14°C and pH 7.8) cultures, and also the crossover experiments - Future cells inoculated into Now medium and incubated under Now conditions (Future in Now), and Now cells incubated in Future medium under Future conditions (Now in Future) were fixed in 1 % glutaraldehyde. Subsamples were mounted in a nanoplankton chamber (Phytotech) and measured with a calibrated eye-piece graticule under an Olympus IX70 inverted microscope. As the fixation process caused coccoliths to separate, the cell size measurements were for the cell body only, which allows more accurate determinations of cell volume (Buitenhuis et al., 2008). Cell volume was calculated assuming that the cells were spherical.

The study was supported by Coasts and Oceans Centre (Strategic Science Investment Fund of the National Institute of Water and Atmospheric Research).