European Ocean Biodiversity Information System

The samples were preserved in borax-buffered 5% formalin (pH 8.5 - 9). The biovolume of the samples was calculated using the displaced volume method, with the largest organisms (>1cm) removed beforehand. The biomass of zooplankton was measured in m1/m3. The zooplankton were identified and counted using stereomicroscopes in counting chambers (with grid of 50 squares with about 1 cm on a side). The spatial and temporal variability of zooplankton during sardine spawning (May) in an area off Porto - Figueira da Foz was analysed. The distribution of zooplankton in the water column indicated a day-night rhythm of vertical migration, since the biomass between 20 and 60 meters depth was significantly higher during the night that during the day. From the application of principal component analysis to the more frequent taxa the following spatio-temporal patterns were obtained: a) A community with neritic characteristics was identified in position to a community with oceanic characteristics. This aspect of spatial variability weighted highly in the total variability of the samples. b) Vertical stratification by taxonomic groups and the influence of hidrodinâmica processes (daily advection) on zooplanktonic communities. c) Changes with time in the distribution of some species seem to have been determined by saline fronts.