CHANGES IN CALCIFICATION AND THE DIMENSIONS OF COCCOLITHS OF EMILIANIA-HUXLEYI (HAPTOPHYTA) GROWN AT REDUCED SALINITIES

The coccolith morphology of three clones of the coccolithophorid Emili ania huxleyi (Lohmann) Hay et Mohler isolated from geographically wide ly 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 deg ree of calcification. For example, decreasing the salinity of the medi um from 34 parts per thousand to 24 parts per thousand led to increase d calcification of parts of the coccolith, such as the central area el ements, but, in some cases, to incomplete formation of the radial elem ents, especially the hammerheads, and around the central tube. At low salinity (14 parts per thousand or 16 parts per thousand) there was ma rked distortion of the coccolith structure, and at 16 parts per thousa nd one clone from the north Atlantic formed coccoliths that were so ma lformed as to be barely recognizable. The morphological observations h ave been complemented with morphometric data that demonstrated that de creased salinity during growth also led to changes in the dimensions a nd relative proportions of the different parts of the coccolith. The r esults demonstrate that not all clones of E. huxleyi respond to salini ty changes in the same way, in terms of both tolerance of low salinity and the effect of reduced salinity on coccolith formation. The observ ations presented here complement other published data indicating the h igh genetic diversity of this species and emphasize the need for cauti on in using coccolith morphology and size variation as criteria for de fining new species within a coccolithophorid genus.