Routine quantification of phytoplankton groups—microscopy or pigment analyses?

Abstract

Phytoplankton pigments in samples taken from nutrient-enriched and non-enriched 3 m 3 seawater enclosures were separated and quantified using high-performance liquid chromatography (HPLC). The enclosures were with and without inorganic (N, P, Si) and organic (glucose, C) nutrient enrichments, resulting in a variation of phytoplankton groups in time and space. The relative contribution of the major phytoplankton groups to the total chlorophyll a (i.e. chlorophyll a plus chlorophyllide a) was estimated by the CHEMTAX program. The results were compared to phytoplankton groups identified and quantified by light and epifluorescence microscopy. For the pigmented flagellate groups the results obtained by microscopy and pigment analyses using the CHEMTAX program showed similar trends. The picocyanobacteria were readily quantified by microscopy and the results were similar to those obtained by flow-cytometry, while the CHEMTAX program for the cyanobacteria revealed different trends. Microscopy and pigment analyses provided similar trends in diatom population development. Estimated diatom contributions to total phytoplankton biomass, however, were considerably higher when based on microscopy than when based on the CHEMTAX program, especially in Si-amended enclosures. Total chlorophyll a:carbon ratios for diatoms were at the lower end of a previously reported range between 1:27 and 1:67. For the pigmented flagellate groups the total chlorophyll a:carbon ratios were above that range. In routine monitoring of phytoplankton we recommend the use of the CHEMTAX program based on HPLC pigment analyses accompanied by a screening for the dominating species by microscopy, and by flow-cytometry for quantification of picocyanobacteria.

Distribution of Synechococcus in the dark ocean

“…The Suruga Bay has siphon-sampling systems, which supply seawater via polyethylene tubes directly to tanks in the underground basement of a land station, from depths of 397 m (tube length 3323 m; inside diameter 200 mm) and 687 m (tube length 7273 m; inside diameter 225 mm). In these systems, differences between tank water levels and seawater levels generate gravity-driven flow, and seawater passes through the tubes at the maximum flow rate of Comparison between epifluorescence microscopy and flow cytometry: Generally, Synechococcus cells are counted with flow cytometry, and similar measurements have been reported with flow cytometry and epifluorescence microscopy in epipelagic samples (Putland & Rivkin 1999, Havskum et al 2004). However, a decrease in the fluorescence of phycoerythrin (PE) has been shown in subsurface samples when using flow cytometry (Olson et al 1990), suggesting that epifluorescence microscopy might fail to detect weakly fluorescent Synechococcus cells in deep seawater samples.…”

Phytoplankton community dynamics during late spring coccolithophore blooms at the continental margin of the Celtic Sea (North East Atlantic, 2006–2008)

“…These samples were preserved using a mixture of alkaline Lugol's iodine solution (0.1% v/v) and borate-buffered formaldehyde solution (0.9% v/v, all final concentrations) (Sherr and Sherr, 1993). The qualitative microscopic screening was performed to verify the presence of the dominant phytoplankton groups in conjunction with specific pigment biomarkers (Havskum et al, 2004;Irigoien et al, 2004). Sea surface water samples (1.0 l) for scanning electron microscopy (SEM) were filtered through polycarbonate membrane filters (0.8 lm pore size, Ø 47 mm, Millipore), dried onboard for 12 h at 50°C and stored dry before being mounted onto microscope slides and coated with gold (Bollmann et al, 2002).…”

The MAREDAT global database of high performance liquid chromatography marine pigment measurements

“…Microscopy and genomics allow for direct identification of algal species and morphology; however, these methods are time-consuming for large-scale surveys, and certain types of taxa or features (e.g., flagella) may be lost or damaged depending on preservation and handling (Havskum et al, 2004). Flow cytometry allows for high sample throughput and information on size and pigment content, but is limited to the smaller size classes of plankton (Li and Wood, 1988).…”