Diatoms and dinoflagellates of the outer aveiro estuary, portugal: Annual variation and ecology

Abstract

Planktonic assemblages of diatoms and dinoflagellates were examined at the mouth of Ria de Aveiro (temperate estuary, NW Portugal) with regard to major physical-chemical variables. Sampling was performed weekly between May 2006 and October 2007, 90 minutes before high tide. Canonical Correspondence Analysis, applied to the abiotic data matrix, revealed a clear temporal variation correlated with temperature. A total of 40 taxa, belonging to 9 different genera of diatoms and 11 genera of dinoflagellates, were quantified. The genera Ceratium, Dinophysis and Protoperidinium were the most represented, followed by Pseudonitzschia and Paralia. The late spring and summer months of 2006 were clearly dominated by dinoflagellate species. CCA analysis revealed two main phytoplankton groups, forced respectively by water temperature and salinity: dinoflagellate species, associated with high temperature and salinity values; and marine diatom species situated opposite to the temperature vector. The majority of the species had their temperature optimum in the range 15.0 – 17.0 ºC. Ceratium longipes had the lowest optimum (13.4 ºC), with Ceratium macroceros having the highest optimum value (18.2 ºC). The year 2006, due to the increase of water temperature has been, for itself, an atypical year, allowing us to foresee the occurrence of different phytoplanktonic assemblages from the ones previously recorded at this latitude.