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Marine Ecology Progress Series

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MEPS 532:29-40 (2015)  -  DOI:

Heme b quotas are low in Southern Ocean phytoplankton

Martha Gledhill1,2,3,*, Loes J. A. Gerringa2, Patrick Laan2, Klaas R. Timmermans2

1Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton SO14 3ZH, UK
2Department of Biological Oceanography, Royal Netherlands Institute for Sea Research, PO Box 59, AB Den Burg (Texel), The Netherlands
3GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstr. 1-3, 24148 Kiel, Germany
*Corresponding author:

ABSTRACT: Heme is the iron-containing prosthetic group of hemoproteins, and is thus required for photosynthesis, respiration and nitrate reduction in marine phytoplankton. Here we report concentrations of heme b in Southern Ocean phytoplankton and contrast our findings with those in coastal species. The concentration of particulate heme b (pmol l-1) observed at the end of the exponential growth phase was related to the concentration of dissolved iron in the culture media. Small Southern Ocean phytoplankton species (<6 µm in diameter) had heme b quotas <1 µmol mol-1 carbon, the lowest yet reported for marine phytoplankton. Heme b was also depleted in these species with respect to chlorophyll a. We calculated the amount of carbon accumulated per mole of heme b per second in our cultures (heme growth efficiency, HGE) and found that small Southern Ocean species can maintain growth rates, even while heme b content is reduced. Small Southern Ocean phytoplankton can thus produce more particulate carbon than larger Southern Ocean or small coastal species at equivalent iron concentrations. Combining primary productivity and heme b concentrations reported for the open ocean, we found that HGE in natural populations was within the range of our laboratory culture results. HGE was also observed to be higher at open ocean stations characterized by low iron concentrations. Our results suggest that low heme b quotas do not necessarily result in reduced growth and that marine phytoplankton can optimize iron use by manipulating the intracellular hemoprotein pool.

KEY WORDS: Iron · Phaeocystis sp. · Diatoms · Haptophyte · Limitation · Coastal phytoplankton · Nutrients

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Cite this article as: Gledhill M, Gerringa LJA, Laan P, Timmermans KR (2015) Heme b quotas are low in Southern Ocean phytoplankton. Mar Ecol Prog Ser 532:29-40.

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