Methodology of Utermöhl phytoplankton

From each bottle, 0.5 l seawater were immediately fixed by adding Lugol solution and stored in a dark refrigerator (4 ºC) until analysis. In the laboratory, subsamples of 50-100 ml were allowed to settle (48 hours) in composite chambers. The cells were identified and counted by using an inverted microscope (tUtermöhl method). The nanoplankton was underestimated because of inadequate preservation and non-settling. As a consequence of the low pH of acid Lugol some calcareous structures such as that of cocolithophorids can presumably be lost. Phytoplankton were identified to the level of species when this was possible o less vaguely defined taxonomic units such as the naked dinoflagellates Gymnodinium/Gyrodinium, Pseudo-nitzschia cf. delicatissima/seriata complex or Navicula spp. Abundance is expressed as cells per ml.