Abstract
Temporal and vertical variations of zooplankton at a station on the north-western Portuguese shelf, close to the Ria de Aveiro inlet, were
studied during two periods of 25 h each in the summer of 1994. Zooplankton sampling was carried out every 2 h, using horizontal plankton
tows (mesh size, 500 µm). Sampling was carried out in two depths, 4 and 12 m. The vertical profiles of salinity and temperature were obtained
immediately before the plankton sampling. Higher zooplankton concentrations were usually observed during the night and at 4 m depth. Most
taxa also occurred inside the Ria de Aveiro, indicating an exchange of planktonic forms between the Ria and the shelf. A classification analysis
of the most abundant taxa suggests some groups, which differ according to taxonomic features and their origin. This was attributed to the high
variability of the forcing agents that affect zooplankton abundance.