A comparison of HPLC pigment analyses and biovolume estimates of phytoplankton groups in an oligotrophic lake.

Abstract

Assessment of the contribution of distinct algal groups to phytoplankton biomass in oligotrophic lakes by marker pigments is compared with assessment by cell-counting biovolume estimates. Seasonal samples from an oligotrophic alpine lake (Redon, Pyrenees) mostly included species of chrysophytes, dinoflagellates, cryptophytes and chlorophytes. The chlorophyl a (Chl a) corresponding to each algal group was estimated using HPLC pigment analyses and the CHEMTAX program. Chl a estimates and biovolume showed a significant correlation for all the groups during the ice-free season except for chlorophytes. However, some of the samples from the initial phase of the ice cover presented a clear departure from the relationship during the ice-free period in most groups. On the other hand, the ratios between a specific marker pigment and the biovolume of the marked algal group were significantly constant within the photic zone (>1% surface irradiance) for most of the pigments and groups, including chlorophytes. Nevertheless, the ratios increased and showed a large variability for samples below the photic depth or below the ice cover. The violaxanthin-chrysophyte biovolume ratio presented an opposed tendency to other pigment-biovolume ratios, which increased in inverse proportion to the depth of the sample. The results are discussed in terms of methodological limitations, acclimation responses and species composition.