coccolith

Coccoliths are microscopic plates of calcium carbonate produced by coccolithophores, a group of single-celled marine algae within the phylum Haptophyta. Each coccolith is a calcite plate that forms part of the cell’s coccosphere, a protective covering around the cell. Coccoliths range in size from about 1 to 10 micrometers and occur in various shapes and ornamentations, from disc-like forms to more elaborate lattices.

Formation and biology: Coccoliths are synthesized inside Golgi-derived vesicles and transported to the cell surface, where they are exocytosed and arranged around the cell to form the coccosphere. The production of coccoliths occurs during cell growth, and as the cell divides, daughter cells acquire a new set of coccoliths. In some species, coccoliths detach from the cell and become part of suspended or deposited sediments. When coccolithophores bloom, large numbers of coccoliths contribute to the calcite content of seawater and surrounding sediments.

Ecology and significance: Coccolithophores contribute substantially to marine carbonate chemistry and the global carbon cycle. Their calcite plates sequester carbon in sediments, and the physical microstructure they create can influence light scattering in the upper ocean. The fossil coccolith record is widely used in biostratigraphy and paleoceanography, helping to reconstruct past temperatures, productivity, and ocean acidity. Chalk deposits, including the White Cliffs of Dover, are rich in coccoliths and illustrate their long geological record.

Notable genera include Emiliania (for example, E. huxleyi), Coccolithus, and Gephyrocapsa.