Changes in calcification and the dimensions of coccoliths of Emiliania huxleyi (Haptophyta) grown at reduced salinities

Abstract

The coccolith morphology of three clones of the coccolithophorid Emiliania huxleyi (Lohmann) Hay et Mohler isolated from geographically widely separated communities has been studied in relation to growth under differing salinity regimes. It was found that reduced salinity caused changes in the overall form of the coccoliths, particularly in the degree of calcification. For example, decreasing the salinity of the medium from 34‰ to 24‰ led to increased calcification of parts of the coccolith, such as the central area elements, but, in some cases, to incomplete formation of the radial elements, especially the hammer-heads, and around the central tube. At low salinity (14‰ or 16‰) there was marked distortion of the coccolith structure, and at 16‰ one clone from the north Atlantic formed coccoliths that were so malformed as to be barely recognizable. The morphological observations have been complemented with morphometric data that demonstrated that decreased salinity during growth also led to changes in the dimensions and relative proportions of the different parts of the coccolith. The results demonstrate that not all clones of E. huxleyi respond to salinity changes in the same way, in terms of both tolerance of low salinity and the effect of reduced salinity on coccolith formation. The observations presented here complement other published data indicating the high genetic diversity of this species and emphasize the need for caution in using coccolith morphology and size variation as criteria for defining new species within a coccolithophorid genus.