Significant CO2 fixation by small prymnesiophytes in the subtropical and tropical northeast Atlantic Ocean

Abstract

Global estimates indicate the oceans are responsible for approximately half of the carbon dioxide fixed on Earth. Organisms p5 lm in size dominate open ocean phytoplankton communities in terms of abundance and CO 2 fixation, with the cyanobacterial genera Prochlorococcus and Synechococcus numerically the most abundant and more extensively studied compared with small eukaryotes. However, the contribution of specific taxonomic groups to marine CO 2 fixation is still poorly known. In this study, we show that among the phytoplankton, small eukaryotes contribute significantly to CO 2 fixation (44%) because of their larger cell volume and thereby higher cell-specific CO 2 fixation rates. Within the eukaryotes, two groups, herein called Euk-A and Euk-B, were distinguished based on their flow cytometric signature. Euk-A, the most abundant group, contained cells 1.8±0.1 lm in size while Euk-B was the least abundant but cells were larger (2.8±0.2 lm). The Euk-B group comprising prymnesiophytes (73±13%) belonging largely to lineages with no close cultured counterparts accounted for up to 38% of the total primary production in the subtropical and tropical northeast Atlantic Ocean, suggesting a key role of this group in oceanic CO 2 fixation.

A global perspective on marine photosynthetic picoeukaryote community structure

“…The high Prymnesiophyceae signal detected across all ocean basins (Supplementary Table 3) supports the observation that 19 0 -hexanoyloxyfucoxanthin, a prymnesiophyte-specific pigment (though also present in a few other Heterokont algae, see Andersen, 2004), often dominates oceanic pigment analyses Liu et al, 2009). Recent fluorescent in situ hybridisation studies confirm the high abundance of these pico-prymnesiophytes in the Atlantic Ocean (Jardillier et al, 2010;Grob et al, 2011;Kirkham et al, 2011b), Indian Ocean and in open ocean regions of the Arctic Ocean . However, Prymnesiophyceae have been consistently underestimated in previous amplificationbased studies using primers targeting the nuclear 18S rRNA gene, potentially a result of PCR bias (Liu et al, 2009).…”

“…Although there is a general trend in the PPE/total picophytoplankton (that is, PPEs þ picocyanobacteria) ratio increasing systematically with increasing latitude and decreasing temperature (Bouman et al, 2012), a considerable amount of variability is observed across the range of latitudes and temperatures. It is important to remember that even at very low cell abundances, PPEs are now known to contribute significantly to marine primary production because of a multifactorial effect of greater biovolume, higher growth rates and high grazing mortality rates (Li, 1994;Worden et al, 2004;Jardillier et al, 2010;Grob et al, 2011). Marine PPE community structure AR Kirkham et al PPE a-diversity Clone sequence data of the 16S rDNA from all the transects studied here (except the BEAGLE and Indian Ocean transects) representing 31 clone libraries allowed us to calculate species richness values (a-diversity) using the Margalef index (Dmg) ( Table 2).…”

“…Together, these data suggest large global distributions of pico-sized prymnesiophytes, which contribute significantly to marine primary production (Cuvelier et al, 2010;Jardillier et al, 2010) even though they mostly lack cultured representatives. The success of these organisms could be because of mixotrophic behaviour (that is, an ability to supplement their phototrophic physiology by preying on bacterioplankton).…”

“…In particular, cloning and sequencing of both nuclear (for example, see Moon van der Staay et al, 2001;Not et al, 2008) and plastid (for example, see Fuller et al, 2006b;MacDonald et al, 2007;Lepère et al, 2009) small subunit rRNA genes have revealed a vast, previously unsuspected diversity within this assemblage. This focus is largely because of the increased recognition of PPEs as key contributors to phytoplankton biomass and primary production across various marine pelagic ecosystems (Li, 1994;Worden et al, 2004;Richardson and Jackson, 2007;Cuvelier et al, 2010;Jardillier et al, 2010;Grob et al, 2011). Moreover, PPEs have recently been shown to be key bacterivores controlling bacterioplankton abundance in both temperate (Zubkov and Tarran, 2008) and oligotrophic gyre (Hartmann et al, 2012) waters.…”

Diversity patterns and activity of uncultured marine heterotrophic flagellates unveiled with pyrosequencing

“…Microbial eukaryotes have key roles in marine ecosystems, particularly in primary production, nutrient cycling as well as for food-web dynamics (Sherr and Sherr, 2008;Jardillier et al, 2010;Caron et al, 2012). Among heterotrophic protists, small flagellates (1-5 mm) constitute a key link between bacteria and larger protists, transferring organic carbon to upper trophic levels (Jurgens and Massana, 2008;Massana, 2011).…”