GENETIC-CHARACTERIZATION OF EMILIANIA-HUXLEYI (HAPTOPHYTA)

Amongst the coccolithophorids, Emiliania huxleyi is the most successfu l and can form large scale blooms under a variety of environmental con ditions. This implies extensive genetic variation within this taxon. P hysiological, morphological and antigenic differences between clonal i solates support this suggestion. Our investigations into the level of genetic variation within the morphological species concept of E. huxle yi indicate that it is such a young taxon that sequence comparisons of both coding and non-coding regions cannot resolve the issue of how ma ny separate taxonomic entities are involved. However, PCR-based geneti c fingerprinting techniques do reveal extensive genetic diversity, bot h on a global scale and within major bloom populations in both space a nd time, Cell DNA content can also separate cells with morphotype A co ccoliths from those with morphotype B coccoliths. Taken together with physiological and morphological evidence, these data suggest that the morphotypes of E. huxleyi should be separated at the variety level. We have used both nuclear and plastid rRNA sequence comparisons to confi rm the place of E. huxleyi within the Haptophyta.