EFFECTS OF IRON ON 2 OCEANIC PHYTOPLANKTON GROWN IN NATURAL NE SUB-ARCTIC PACIFIC SEAWATER WITH NO ARTIFICIAL CHELATORS PRESENT

Two oceanic phytoplankters were isolated from the NE subarctic Pacific Ocean and grown in unenriched Station P (145 degrees W, 50 degrees N) seawater to which no trace metals nor artificial chelators were added . Basic physiological parameters were measured for the two species (a coccolithophore, Emiliania huxleyi (Lohman) Hay et Mohler and a diatom , Actinocyclus sp.) in the Station P seawater, and in the same seawate r to which 5 nM total Fe was added (without chelators). In the Station P seawater with no Fe added, the coccolithophore grew maximally, whil e the diatom was unable to divide after three generations. The coccoli thophore did not show signs of physiological stress due to Fe limitati on under the simulated Station P experiment. When 5 nM total Fe was ad ded to the seawater, the diatom resumed cell division at a maximal rat e, outgrowing the coccolithophore. Laboratory experiments conducted wi th EDTA present further illustrated that Emiliania huxleyi (Lohman) Ha y et Mohler is better adapted to the typical low Fe conditions found a t Station P than large diatoms. These results provide independent, phy siologically based support for the role of Fe in controlling phytoplan kton species composition in the NE subarctic Pacific Ocean. (C) 1997 E lsevier Science B.V.