ROLES OF NITROGEN AND PHOSPHORUS IN COCCOLITH FORMATION IN EMILIANIA-HUXLEYI (PRYMNESIOPHYCEAE)

Effects of nitrogen (N) and phosphorus (P) limitation on calcification and coccolith production in Emiliania huxleyi were investigated in ba tch and chemostat cultures by means of chemical analyses of calcium (C a) and organic carbon (C), counts of coccoliths and cells, and scannin g electron microscopy. In a normally calcifying (C-cell) clone growing in the absence of nutrient limitation in batch or semicontinuous cult ures, c. 36 attached plus detached coccoliths were present per cell. I n batch cultures as well as in chemostats, the number rose to 70-120 w hen either N or P became strongly limiting. The molar Ca/C ratio, meas ured in chemostats, showed a corresponding increase from 1.07 to c. 1. 38. The two types of limitation had opposing effects on the calcificat ion of individual coccoliths: the mean Ca content of a coccolith decre ased from a normal value of 0.60 pg to 0.46-0.49 pg under N limitation , and increased to 0.67-0.73 pg under P limitation. These effects were accompanied by corresponding modifications of coccolith morphology. I n batch cultures of one naked (N-cell) clone grown to the stationary p hase, P limitation but not N limitation induced the formation of c. 40 coccoliths per cell; these coccoliths were of aberrant shape. In anot her N-cell clone, P limitation had no such effect. The results suggest on one hand that coccolith formation is generally less dependent on N and P nutrients than is cell replication and on the other hand that s tages exist in the growth and calcification of a coccolith that are sp ecifically influenced by either N- or P-containing cell constituents.