Routine determination of plankton community composition and size structure: a comparison between FlowCAM and light microscopy

Samples from a monthly monitoring programme in the Cantabrian Sea were analysed with a FlowCAM-based automated technique. The estimates of abundance, biomass size spectra and taxonomic diversity of nano- and microplankton communities were compared with those obtained by traditional microscopical analysis of the same samples. The structure and abundance of a preserved plankton sample determined using FlowCAM showed minimal differences compared with traditional microscopical estimates. The effects of sample preservation and inaccuracies in the automatic classification are the main causes of discrepancies in the size structure determination between the two approaches. However, the synoptic understanding of the seasonal variation in the abundance, biomass and diversity obtained from the two methods is similar. Our results suggest that the natural variations in the community attributes explored are of greater magnitude than the error introduced by the methods and that the fully automatic method is adequate to explore these variations.