DescriptionCoccoliths are calcium carbonate exoskeletons produced by some unicellular marine algae referred to as coccolithophores. Large coccolithophore blooms play a significant role in the Earth’s biogeochemical cycling and these blooms can often be seen from space. Despite numerous studies on coccoliths we still lack a complete understanding of their function. To test whether coccoliths enhance photosynthesis by amplifying incident radiation I measured bio-optical properties of the common coccolithophore Emiliana huxleyi. Variable fluorescence and absorption spectroscopy measurements of E. huxleyi cells with and without coccoliths (removed by bubbling CO2 into the media) suggest that coccoliths do not enhance the light within cells, and if anything, shade them slightly due to increased scattering. This indicates that calcification does not provide any optical advantage for individual cells. Bubbling E. huxleyi with CO2 to remove the coccoliths led to acidification of the media and stimulated ΔpH-related non-photochemical quenching (NPQ) and reduced net photosynthesis. The reason for the reduction in net photosynthesis is unclear, as it does not appear to be entirely a consequence of stimulated NPQ. My results suggest that there is no photonic effect of coccoliths that has a biological function.