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

Abstract 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.