Estimating the carbon flux through main phytoplankton groups in the northwestern Mediterranean

Abstract

We performed dilution experiments and primary production measurements in surface waters during a cruise in the northwestern Mediterranean Sea in June 2000 to quantify the carbon (C) flux through phytoplankton groups that can be distinguished by their pigment markers. Pigments in the dilution experiments were measured by highpressure liquid chromatography (HPLC). Pigment per cell and synthesis rates of photoprotectant versus light-harvesting pigments indicated that cells did not undergo photoacclimation during the 24-h dilution experiments. Mean chlorophyll a (Chl a) concentration was 0.128 mg m Ϫ3 , and mean primary production was 4.99 mg of C m Ϫ3 d Ϫ1 . Prymnesiophyceae contributed 51% of the total Chl a, green algae 21%, diatoms 13%, cyanobacteria 6%, and Pelagophyceae and Dinophyceae 4% each. Size fractionation showed that 68% of total phytoplankton were Ͻ5 m. A mean growth rate of 0.89 d Ϫ1 was completely offset by a mean grazing rate of 1.01 d Ϫ1. Growth and mortality were also balanced for the individual phytoplankton groups, with highest rates for diatoms and lowest for green algae. Despite the high growth rates measured, nutrient-amended incubations showed that these rates were nutrient limited, although to a different extent for each group. Green algae experienced the most severe limitation and cyanobacteria the least. The comparison of C incorporation rates and Chl a synthesis rates permitted the estimation of a C : Chl a ratio of 47 (g : g) for newly produced organic matter in the study area. This value, corrected for the different degree of nutrient limitation, was used to estimate the C flow through the different phytoplankton groups. Because of their high growth rates, diatoms played a disproportionate role in the C flux compared to their biomass contribution.

Chemotaxonomic phytoplankton patterns on the eastern boundary of the Atlantic Ocean

“…The haptophytes in the northern and southern oligotrophic regions were most likely in the form of picoeukaryotes, since flow cytometry indicated the dominance of picoeukaryotes and picoprokaryotes in oligotrophic waters of the Atlantic Ocean (Zubkov et al, 1998, 2000; Tarran et al, 2006). Similarly, a complementary investigation of size-fractionation and chemotaxonomy of summer phytoplankton in the oligotrophic NW Mediterranean demonstrated the dominance of haptophytes that were mostly o5 mm (Latasa et al, 2005).…”

Effects of experimental warming and increased ultraviolet B radiation on the Mediterranean plankton food web

“…Microbial plankton carbon biomass estimates-Microbial carbon biomass was estimated using the following carbon conversion factors: 20 fg C cell 21 for bacteria (SimeNgando et al 1995), 0.22 pg C mm 23 for HF (Booth 1993), and 0.21 pg C mm 23 for ciliates (Putt and Stoecker 1989); a C : Chl a ratio of 57 was used to estimate the carbon biomass of phytoplankton (Latasa et al 2005). Total microbial carbon biomass was then computed as the sum of the estimated carbon biomass of bacteria, phytoplankton, heterotrophic flagellates, and ciliates.…”

Modelling the effect of vertical mixing on bottle incubations for determining in situ phytoplankton dynamics. I. Growth rates

“…that the increase in chlorophyll is matched by the increase in carbon so that the former may be used as proxy for the determination of the carbon-based growth rate μ C . Although most experimentalists are aware of this problem (Brown et al 2002, Latasa et al 2005, Gutiérrez-Rodríguez et al 2010) it remains difficult to provide an accurate quantification of the associated error.…”