Growth and calcification in the coccolithophorid Emiliania huxleyi (Haptophyceae) at low salinities

Clones of the coccolithophorid Emiliania huxleyi (Lohmann) Hay et Mohler were compared in a salinity–growth experiment. Five clones from Scandinavian coastal water grew well at 12‰, a salinity which did not support growth of any of three offshore Atlantic clones or three warm water clones. With one exception, the lower salinity limit for growth of noncoastal clones was 16‰ or higher. This suggests that E.huxleyi has developed distinct ecotypes in Scandinavian coastal waters. In one coastal clone, dissolved inorganic carbon was shown not to limit growth at either 17‰ or 34‰ salinity. Chemical analyses and 14C incubations indicated that the molar ratio of calcite production to organic carbon production in this clone declined from 0.75–0.80 at 25–34‰ salinity to c. 0.60 at 17‰ salinity. The mean amount of calcium deposited in each coccolith declined from 0.67 pg at 34‰ to 0.43 pg at 17‰ salinity. The number of attached plus detached coccoliths per cell, c. 30–40, did not decrease with decreasing salinity. No significant salinity effect on calcite dissolution was found in killed cultures. Scanning electron microscopy and image analysis based on light microscopy demonstrated an increased undercalcification and a shortening of the distal shield elements in coccoliths formed at low salinities. The findings were in general agreement with observations from an E.huxleyi bloom in the Oslofjord, Norway.