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PLANKTON IN NITROQEN AND PHOSPHORUS OY-S
NH; concentration (pM1
FIQ. 6. Calculated specific growth rates of four marine phytoplankton species as a
function of (A) nitrate and (B) ammonium concentration. The growth rates
correspond to an irradiance level of 20% of that due to sunlight at the sea surface.
a = Coccolithw huxleyi. b = Dilylum brightwellii. c = Skeletimema coatalum and
d = Dunaliella tertiolecta. (After Eppley et al., 1969b.)
levels the growth of Coccolithus huxleyi (Lohm.) Kampt would be
favoured ; whereas at higher levels, the diatoms would predominate.
Changes in the phytoplankton in accord with this have actually been
observed off southern California where upwelling can increase the
nitrate level of the surface waters (R. W. Eppley, unpublished data).