A limited set of six keystone taxa has been selected to fulfil the objectives of this project. Criteria for taxon selection were
(1) They must be capable of being maintained in culture.
(2) They should be significant components of the marine flora.
(3) Their coccoliths should be readily preserved yielding a useful geological record.
(4) Detailed study of some aspects of their biology and geology should have already been carried out.
(5) The taxa taken together should provide an overview of the coccolithophorids, a set of taxon pairs of varying degrees of relatedness, and a set of taxa at increasing taxonomic separation from the single best studied coccolithophorid - Emiliania huxleyi .
The selected taxa are: Gephyrocapsa spp (a plexus of closely related species), Calcidiscus leptoporus, Coccolithus pelagicus, Umbilicosphaera sibogae, Helicosphaera carteri, and Syracosphaera pulchra. The relationship of these taxa to other coccolithophorids is shown in the figure below (click fig to open high res. version of the image - about 224kB).
A prime objective of the CODENET project is to investigate microevolution and species level variation. In the coccolithophorids, and most other groups of organisms, there is little consensus as to what constitutes a species, so to avoid this problem we have adopted broad species concepts, including in our study all morphospecies which might arguably be sub-species or variieties of the core species (e.g. for this study we include within Helicosphaera carteri the very similar species H. hyalina and H wallichii which are only separated on single morphological characters of dubious taxonomic significance, but exclude H. pavimentum which is separated on a wide range of criteria).
E. huxleyi is numerically the most abundant coccolithophoriod in the modern oceans. It is not formally included in the CODENET project since it has been extensively studied (especially during the EC-MAST EHUX project) and so similar studies to those which we will be carrying out have mostly been performed on E. huxleyi . We will, however, integrate all such data into our studies, and possibly carry out limited additional studies on the species. In addition we will closely co-ordinate out work with continuing studies of E. huxleyi being carried out within the GEM initiative.
This page is based on the CODENET proposal, as accepted for funding by TMR, June 1997