Temporal variation in phytoplankton assemblages and pigment composition at a fixed station of the Ria of Pontevedra (NW Spain)

Phytoplankton composition and abundance were studied at a fixed station (P2, Ria of Pontevedra, NW Spain) weekly during a 2-year period (1999-2000). In addition to microscopic cell counts, a chemotaxonomic approach based on HPLC pigment analysis and CHEMTAX data processing was studied on two size classes. The contribution of the picoplankton fraction to the total chlorophyll (chl) a averaged 13 +/- 10%. Pigment suites of the picoplankton fraction were mainly provided by picoeukaryotes. Chl b dominated in the picoplankton whereas chls c (c(2), c(1) and c(3)) were the major accessory chlorophylls in the micro-nanoplankton. Despite this, fucoxanthin was by far the most abundant carotenoid in both size classes (often >70% of total carotenoids). Major 'pigment groups' in the picoplankton were 'prasinophytes' (with prasinoxanthin and carotenoids of the uriolide series) and 'chlorophytes', which contributed up to 60% total chl a during winter. 'Diatoms' and 'haptophytes' were other relevant picoplanktonic groups along the seasonal cycle. Micro-nanoplankton was dominated by 'diatoms I' (chl c(1) and chl c(2)) and 'diatoms II' (chl c(3) and chl c(2)), which contributed up to 70% of total chl a in spring. Chl c composition during diatom blooms exhibited higher chl c(1) : chl c(2) ratios in winter spring and higher chl c(3): chl c(2) ratios in summer-autumn. (C) 2003 Elsevier Ltd. All rights reserved.