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Aquatic Microbial Ecology

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AME 35:79-91 (2004)  -  doi:10.3354/ame035079

Phytoplankton community response to a manipulation of bioavailable iron in HNLC waters of the subtropical Pacific Ocean

Melanie L. Eldridge1, Charles G. Trick3, Melissa B. Alm4, Giacomo R. DiTullio4, Eden L. Rue5, Kenneth W. Bruland5, David A. Hutchins6, Steven W. Wilhelm1,2,*

1Department of Microbiology, and
2Center for Environmental Biotechnology, The University of Tennessee, Knoxville, Tennessee 37996, USA
3Department of Biology, The University of Western Ontario, London, Ontario N6A 5B7, Canada
4Grice Marine Laboratory, College of Charleston, Charleston, South Carolina 29412, USA
5Department of Ocean Sciences, The University of California Santa Cruz, Santa Cruz, California 95064, USA
6College of Marine Sciences, The University of Delaware, Lewes, Delaware 19958, USA
*Corresponding author. Email:

ABSTRACT: Studies in high nutrient, low chlorophyll (HNLC) regions have demonstrated that increased Fe availability results in an increase in phytoplankton biomass and changes in community composition. Here we present experiments in which the availability of iron (Fe) was increased or reduced to monitor the response of individual groups of phytoplankton (large eukaryotes, picoeukaryotes and cyanobacteria) by flow cytometry. Additions (0.5 to 5.0 nM Fe) and reductions in available Fe (through addition of 1 to 10 nM of the fungal siderophore desferrioxamine B) were made to enclosed communities from the South American eastern boundary current off Peru, where ambient dissolved Fe concentrations were <100 pM. As predicted, chlorophyll concentrations increased in the added Fe treatments relative to the control, indicative of Fe limitation. Flow cytometry demonstrated that this was due to increases in the abundance of large eukaryotes that are Fe-starved under ambient conditions. Cyanobacterial abundance increased and decreased linearly with Fe availability, suggesting that cyanobacteria were Fe-limited but not Fe-starved. In contrast, picoeukaryote cell abundance increased with decreasing Fe availability, although chlorophyll cell-1 in this group responded in an inverse manner. The results demonstrate that members of the marine phytoplankton community respond differently to Fe availability, which may influence the outcome of biological competition among organisms in Fe-limited environments.

KEY WORDS: Fe limitation · Fe Uptake · Desferrioxamine B · Picoeukaryotes

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