Biology and paleontology of coccolithophores (Haptophytes)

Abstract

Coccolithophores are marine unicellular haptophytes that possess calcified scales called coccoliths. They are classified primarily on the morphology and crystallography of the coccoliths. This classification is well supported by molecular genetic results; however, a significant complication occurs in that coccolithophores have a haplodiplontic life cycle with asexual reproduction by binary fission in both the diploid and haploid phases and with very different types of coccoliths being produced in the two phases. Coccolithophores have very extensive fossil records, making them an attractive group for study of microevolutionary patterns through combined study of molecular genetics, the morphology of living species and the fossil record. The molecular studies showed that many conventional coccolithophore Morpho-Species consist of multiple discrete species often only differing from each other in minor morphological features or the size range of coccoliths. Paleontological studies showed that many fossil lineages had evolutionary size- increasing events in their history, and the size ranges of some fossil species are useful as index fossils for dating of marine sediments. Stratigraphic variations of the composition of fossil species and organic compounds (alkenones) produced by the Isochrysidales are useful for reconstruction of sea surface water condition and of sea surface temperature in the geological past. It is possible that ongoing global warming and ocean acidification may affect the distribution of coccolithophores and the composition of genotypes/species.