Phytoplankton community during a coccolithophorid bloom in the Patagonian Shelf: microscopic and high-performance liquid chromatography pigment analyses

Abstract

We describe the phytoplankton community and biomass during a summer coccolithophorid bloom sampled over the Patagonian shelf (48.58S-50.58S). Those phytoplankton species can contribute to the flux of calcium carbonate out of surface waters. Results from both microscope and high-performance liquid chromatography (HPLC) analysis are shown to complement information on the phytoplankton community. From CHEMTAX analysis of HPLC data, the most important organisms and groups identified were the coccolithophorid Emiliania huxleyi, the haptophyte Phaeocystis antarctica, dinoflagellates, diatoms, cryptophytes, prasinophytes and cyanobacteria. Phytoplankton microscope counts were converted into phytoplankton group-specific biovolume estimates. Although some microscope-identified taxa could not be determined by CHEMTAX, e.g. the autotrophic ciliate Myrionecta rubra, cluster analyses from both techniques showed similar results for the main groups. Both Emiliania huxleyi cell concentration and biomass, and the pigment 19 ′ -hexanoyloxyfucoxanthin were the most important biological features during the sampling period. At surface, nitrate was moderately high (0.2 -4.2 mM) in coccolithophorid-dominated samples, whereas phosphate (,0.33 mM) and silicate (,1.35 mM) concentrations were low. Among the environmental factors low Si:N ratios were mainly associated with the dominance of E. huxleyi. Competition and probably differential grazing could also promote a coccolithophorid outgrowth over other photoautotrophs during the summer season in the Patagonian shelf.

Seasonal change of phytoplankton (spring vs. summer) in the southern Patagonian shelf

“…Concentrations of phosphate (o0.25 mM) and silicate ( o0.40 mM) were, in turn, low and variable over the sampling region (data not shown). A similar nutrient distribution pattern was observed in the summer cruise, although with higher concentrations, reaching up to 4.77 mM of DIN, 0.33 mM of phosphate and 1.35 mM of silicate (see de Souza et al (2012), for further details). Such spatial gradients in DIN have already been reported for the region in summertime, when higher concentrations of nutrients were associated with a nutrient-enriched SASW, decreasing towards the inner shelf low salinity waters Valiadi et al, 2014).…”

“…Those organisms were accompanied by smaller percentages of small flagellates (green flagellates and other flagellates) and peridinin-containing dinoflagellates. By contrast, in summer, greater spatial variability was observed (see de Souza et al (2012)) when the 'other flagellates' group (sum of Emiliania huxleyi and Phaeocystis antarctica) and dinoflagellates were predominant (Fig. 3).…”

“…The first cruise was conducted in the austral spring season (21-22 Oct 2007), when 9 stations were occupied and the second cruise in austral summer (04-07 Jan 2008) with 18 stations sampled. The structure of the phytoplankton community and the bio-optical characteristics of a coccolithophore bloom during the summer cruise 2008 have been described in de Souza et al (2012) and Garcia et al (2011), respectively. Water samples for biological and chemical analyses were collected using Niskin bottles attached to a combined rosette þ CTD SeaBird s 911 carrousel system.…”

“…The biotic matrix Table 2 Input and output ratios of marker pigments to Chl a in the spring cruise. was composed by biomass of the main phytoplankton taxonomic groups determined from HPLC/CHEMTAX analysis, taking into account strong associations with the microscopic data (see de Souza et al (2012), for further details). The environmental matrix included the following variables: surface temperature, salinity, DIN, phosphate, silicate, UMLD and stability.…”

“…Spatial patterns of phytoplankton distribution have been studied along the Patagonian shelf by remote sensing (Gonzalez-Silvera et al, 2006;Signorini et al, 2006;d'Ovidio et al, 2010;Dogliotti et al, 2014) and in situ sampling for phytoplankton composition (Garcia et al, 2008;Painter et al, 2010;de Souza et al, 2012;Segura et al, 2013;Balch et al, 2014). However, there is scarce data on changes in phytoplankton community over consecutive seasons in the region (Segura et al, 2013 series from remote sensing and historic hydrographic data, Signorini et al (2006) showed that the seasonal variability and succession of phytoplankton groups along the Patagonian shelf-break respond to light intensity and nutrient supply within the mixed layer, driven by seasonal changes in the water column structure: an early spring bloom dominated by diatoms associated with high nutrient levels is replaced by coccolithophore-dominated summer blooms related to shallow upper mixed layer depth (UMLD).…”