THE ELEMENTAL COMPOSITION OF SOME MARINE PHYTOPLANKTON¹

Abstract

We analyzed the cellular content of C, N, P, S, K, Mg, Ca, Sr, Fe, Mn, Zn, Cu, Co, Cd, and Mo in 15 marine eukaryotic phytoplankton species in culture representing the major marine phyla. All the organisms were grown under identical culture conditions, in a medium designed to allow rapid growth while minimizing precipitation of iron hydroxide. The cellular concentrations of all metals, phosphorus, and sulfur were determined by high-resolution inductively coupled plasma mass spectrometry (HR-ICPMS) and those of carbon and nitrogen by a carbon hydrogen nitrogen analyzer. Accuracy of the HR-ICPMS method was validated by comparison with data obtained with 55 Fe radioactive tracer and by a planktonic reference material. The cellular quotas (normalized to P) of trace metals and major cations in the biomass varied by a factor of about 20 among species (except for Cd, which varied over two orders of magnitude) compared with factors of 5 to 10 for major nutrients. Green algae had generally higher C, N, Fe, Zn, and Cu quotas and lower S, K, Ca, Sr, Mn, Co, and Cd quotas than coccolithophores and diatoms. Co and Cd quotas were also lower in diatoms than in coccolithophores. Although trace element quotas are influenced by a variety of growth conditions, a comparison of our results with published data suggests that the measured compositions reflect chiefly the intrinsic (i.e. genetically encoded) trace element physiology of the individual species. Published field data on the composition of the planktonic biomass fall within the range of laboratory values and are generally close to the approximate extended Redfield formula given by the average stoichiometry of our model species (excluding the hard parts):While clearly this elemental stoichiometry varies between species and, potentially, in response to changes in the chemistry of seawater, it provides a basis for examining how phytoplankton influence the relative distributions of the ensemble of major and trace elements in the ocean.Abbreviation: HR-ICPMS, high-resolution inductively coupled plasma mass spectrometry Over the past two decades, both culture and field studies have revealed that trace metals can be important in controlling primary production and regulating the community structure of marine phytoplankton. For 1

Seasonal phosphorus and carbon dynamics in a temperate shelf sea (Celtic Sea)

“…Heterotrophic bacteria are recognised as strong competitors for P i under nutrient depleted conditions (Thingstad et al, 1993(Thingstad et al, , 1996Duhamel and Moutin, 2009). Whilst phytoplankton cellular C:P stoichiometry is near, or slightly lower, than the canconical Redfield ratio (Geider and LaRoche, 2002;Ho et al, 2003), bacterial cellular C:P ratios are significantly more P-rich (e.g., ~50; Fagerbakke et al, 1996;Sterner and Elser, 2002;Hessen et al, 2004;Duhamel and Moutin, 2009; see also Scott et al, 2012).…”

“…These observations led to the paradigm that plankton consume inorganic N and P in the same proportion as they are availability, fixing them into particulate organic material which is eventually decomposed, returning N and P back into their inorganic forms (Redfield et al, 1963). This paradigm of elemental stoichiometry has been used to link plankton production to the biogeochemical cycling of C, N and P. However, it is also recognised that important deviations from the canconical Redfield ratio may occur in the biochemical composition of marine plankton (e.g., Geider and La Roche, 2002;Ho et al, 2003;Finkel et al, 2006), trophic interactions (e.g., Sterner and Elser, 2002;Hessen et al, 2002Hessen et al, , 2004 and biogeochemical processes (e.g., Arrigo, 2005;Bozec et al, 2006;Bauer et al, 2013).…”

Variability in calcitic Mg/Ca and Sr/Ca ratios in clones of the benthic foraminifer Ammonia tepida

“…Despite the removal of organics with NaOCl it was clear from the time resolved laser signals that some cytoplasm, with elevated Mg and Zn, remained on the outside and inside of a few chambers. Zinc is known to be concentrated by phytoplankton (Ho et al, 2003), adding to the intracellular concentrations in the foraminifera when taken up as food. Parts of analyses, towards the outside or inside of the test wall, with elevated Mg and Zn were omitted from the integration (Fig.…”

A generalized model of pelagic biogeochemistry for the global ocean ecosystem. Part I: Theory

“…Therefore a value of 2-3 represents the minimum internal ratio for cell survival, but it is not simple to find one single constant value representative of the optimal cellular requirement (Sunda, 1997). Ho et al (2003) derived an optimal value of 60 for the average stoichiometry of the soft tissues of some marine phytoplankton species cultivated in non-limiting media ((C 124 ) 1000 Fe 7.5 ). Data from Sunda and Huntsman (1995) show that saturation of growth rate is achieved when the intracellular ratio is above 20, depending on light conditions.…”