Mann, E. L.. Woods Hole Oceanographic Institution and Massachusetts Institute of Technology, emann@mit.edu
Chisolm, S. L.. Woods Hole Oceanographic Institution and Massachusetts Institute of Technology, chisholm@mit.edu

 
THE GROWTH RATE OF PROCHLOROCOCCUS IN THE EASTERN EQUATORIAL PACIFIC IS LIMITED BY IRON
 
The prokaryotic picoplankter Prochlorococcus is a dominant member of the phytoplankton community in the eastern equatorial Pacific, a high-nutrient, low-chlorophyll area. During an in situ iron fertilization experiment (IronEx II) chlorophyll per cell and cell size increased in Prochlorococcus, but cell numbers remained constant. In order to determine whether their growth was stimulated by the iron addition, we estimated the intrinsic growth rate (i.e. the growth rate in the absence of cell losses due to grazing) using three independent methods based on cell cycle analysis and diel changes in cell number and size. These analyses showed that iron increased the intrinsic growth rate of the cells on average 30 to 64% relative to that measured prior to iron fertilization of 0.61 per day. In addition, cells incubated on deck with 3.6 fold more iron than in the patch had even higher intrinsic growth rates that approached two doublings per day. Prochlorococcus mortality also increased after the addition of iron, from 1.09 to 1.76 per day. We conclude that the intrinsic growth rate of Prochlorococcus in the equatorial Pacific is significantly iron limited, but no increase in cell numbers inside the iron-enriched patch was observed because growth and mortality were balanced.
 
Day: Thursday, Feb. 4
Time: 03:45 - 04:00pm
Location: Sweeney Center
 
Code: SS28TH0345S