Genetic and physiological variation in pigment composition of Emiliania huxleyi (Prymnesiophyceae) and the potential use of its pigment ratios as a quantitative physiological marker

Genetic variation of pigment composition was studied in 16 different strain s of Emiliania huxleyi (Lohm.) Hay et Mohler in batch culture. Distinct str ain-dependent differences were found in the ratios of fucoxanthin, 19'-hexa noyloxyfucoxanthin, and 19'-butanoyloxyfucoxanthin, hampering the use of th ese individual pigments as a taxonomic marker at the species level. The mol ar ratio of total carotenoids to chl a, however, was constant for all strai ns tested. In addition, the pigment composition of one axenic strain (L) of E. huxleyi at different growth rates in light-, nitrate-, and phosphate-li mited continuous cultures tvas analyzed quantitatively. The pigments fucoxa nthin and 19'-hexanoloxyfucoxanthin correlated closely under all conditions . From steady-state rate calculations, it is hypothesized that 19'-hexanoyl oxyfucoxanthin is synthesized from fucoxanthin, with light as a modulating factor. The net rate of synthesis of diatoxanthin depended both on the conc entration of diadinoxanthin (its partner in the xanthophyll cycle) and on l ight, illustrating its photoprotective function in the xanthophyll cycle. I n axenic strain L, the ratio of total fucoxanthins to chl a correlated stro ngly with photon flux density and can potentially be used to assess the phy siological status with respect to irradiance in field populations. In multi specific bloom situations, the ratio of diadinoxanthin plus diatoxanthin to total fucoxanthins could be used as an alternative indicator for the light -dependent physiological state of E. huxleyi, provided that no other chromo phytes are present. Application of these correlations to mesocosm data from the literature has so far provided no evidence that E. huxleyi blooms form only at inhibiting light levels, as previously suggested.