The parameters that were considered as being able to give indications about the state of zooplanktonic populations were the abundance (biovolume) and the specific and population structures of the epi- (living in the 0 to 150 meters deep) and mesoplanktonic (living in the layer from 150 to 1000 meters deep). The abundance (biovolume) as well as the specific and population structures of epi- (living in 0 to 150 meter depth) and mesoplanktonic (living in 150 to 1000 meter depth) communities were used to assess the condition of zooplanktonic populations.

Zooplankton was sampled in four radials, with three coverings in radial 1 with a two-day interval and just one covering in radials 2, 3, and 4. The current study was based on samples conducted aboard the NRP "Almeida Carvalho" during cruise CECIR XIV from the 3rd to the 9th of May 1988 in the coastal area between Porto and Figueira da Foz. The samples were collected using a WP2 plankton net. The trawls were conducted in a vertical direction at a speed of 1 m/s, stratified between the depth levels of 0-20 m, 20-60 m, and 60-150 m, resulting in a total of 99 zooplankton harvests.