Biogeography of Emiliania huxleyi

Where have blooms of Ehux been observed in the sea? A survey of literature on these blooms in the field (where a bloom is defined as a cell concentration exceeding 1000 cells ml-1) indicates the following locations:

1. The North Atlantic (Holligan et al, 1993a; Malin et al, 1993).
2. The North Sea (Holligan et al, 1993b; Wal et al, 1995).
3. The Norwegian fjords (Braarud, 1945; Birkenes & Braarud, 1952; Berge, 1962; Braarud et al, 1974; Paasche & Kristiansen, 1982; Kristiansen et al, 1994).
4. The Gulf of Maine (Townsend et al, 1994).
5. Close to the Scilly Isles (to the west of the English Channel) (Garcia-Soto et al, 1995).
6. The Southern Benguela Upwelling (Mitchell-Innes & Winter, 1987).
7. The Skaggerak (Pingree et al, 1982).
8. The Celtic and Armorican shelf region (Holligan et al, 1983).

Analysis of the literature accounts reveals a common hydrographic feature associated with all known blooms of Ehux: they all occur in highly stratified water where the mixed layer depth is usually ~10--20m, and is almost always <=30m. This assertion holds true for all of the blooms above with the exception of the last. The coincidence between Ehux and shallow stratification (and the implications for a possible high light requirement for Ehux) is discussed in more detail in (Nanninga & Tyrrell, 1996).

A second and very valuable source of information about the biogeography of Ehux comes from satellite imagery. Because of this, we know more about the distribution of blooms of Ehux than we do for any other species. The light-scattering by coccoliths means that satellite images can give us an instantaneous high-resolution picture of the total spread of a demonstrably single-species bloom, which is not possible for other species.

One study has analysed a global dataset of satellite images from the CZCS satellite during the years 1979-1985. An algorithm was constructed for detecting coccolithophore blooms (which will almost all be Ehux), and then applied over the global, multi-year dataset to gain an estimate of the global distribution of the species. The resulting map of Ehux blooms is shown here

A general review of the biogeography of all coccolithophore species (including Ehux) is given by Winter et al (1994).


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