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Living coccolithophores have a widespread oceanic distribution, living in the photic zone and being most diverse at low latitudes. Generally speaking, they are rare or absent at latitudes higher than 70° and flourish in warm, stratified, oligotrophic, mid-ocean environments. A number of species have very broad ecological tolerances but only one freshwater coccolithophore has been well documented.
Coccolithophores show distinct biogeographic distribution patterns, defining broad, latitudinal belts or zones. These zones are distinguished by variations in population composition, although a limited number of species show restricted distribution, limited, for example, to the low or high latitudes. These distribution patterns reflect both temperature and nutrient distributions and are linked to large-scale features of oceanic circulation, such as, divergence zones, ocean gyres and seasonal mixing. The major limiting nutrients are nitrate and phosphate, but the abundance of other trace elements and vitamins, such as Fe, Zn, Mn and thiamine, are also thought to be significant. Some coccolithophores may supplement their nutrient requirements by heterotrophy or phagotrophy, using the haptonema to capture food particles. Seasonally stable, oligotrophic, tropical and subtropical mid-ocean gyre environments support the highest diversities, but standing crops are low, reflecting low reproduction rates. Eutrophic conditions, due to upwelling or deep seasonal mixing, often support high standing crops dominated by one or a few species, however diatoms are the most effective eutrophic phytoplankton in present oceans and coccolithophores generally bloom following depletion of silica in the surface waters. Continental shelf and near shore environments also tend to be unstable and eutrophic in nature and support distinctive assemblages, including taxa, which do not live in open-ocean environments, e.g.Braarudosphaera bigelowii and Pleurochrysis carterae.
Coccolithophore communities also show vertical stratification, with distinctive deep photic-zone assemblages occurring in or below the thermocline/nutricline, exploiting a less-competitive low-light, low-temperature, high-nutrient niche, in particular, Florisphaera profunda and Gladiolithus flabellata.
Evidence from the fossil record suggests that coccolithophores have always displayed broadly similar ecological tolerances, and certainly palaeobiogeographic distributions are generally comparable with those of the present.
