EFFECTS OF UNBALANCED NUTRIENT REGIME ON COCCOLITH MORPHOLOGY AND SIZE IN EMILIANIA-HUXLEYI (PRYMNESIOPHYCEAE)

Single coccoliths of Emiliania huxleyi grown in mesocosm enclosures (6 0 degrees 16'N, 05 degrees 14'E, May-June 1991) under different N:P re gimes were analysed in a scanning electron microscope. The results ind icate that only E. huxleyi with Type A coccoliths was present in the e nclosures. Approximately 80-90% of the total coccolith assemblages had developed normally, whilst the remainder were malformed, incompletely grown or dissolved. Severely under-calcified specimens were rare and dissolution and breakage less than 5 %. The coccoliths were of larger size than normal, as has been found previously in fjords of southweste rn Norway supporting the conclusion that a local population of E. huxl eyi has developed, specific to these waters. Both phosphorus and nitro gen stress caused significant changes in coccolith size and evidence o f malformation was clear, particularly in the low-phosphate enclosure. Although the observations presented here concern only Type A coccolit hs and it is not known how nutrient stress may affect the coccoliths o f the other types of E. huxleyi, they do serve to stress the fact that environmental conditions may possibly obscure genetically determined features. Following our observations on coccolith morphology in relati on to nutrient status in enclosures, it will be of interest to test wh ether a similar correlation can be detected in the natural environment .