During the KEOPS survey, zooplankton was sampled with vertical tows to estimate zooplankton stock and to study its composition and size structure both using traditional taxonomic identification and Optical Plankton Counter (OPC). Mesozooplankton OPC-biomass derived from OPC size spectra and integrated over 200 m was variable with average values about 10 g C m
−2 along transects A and B and at the fixed station KERFIX, and only
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5 g C m
−2 along transect C. Stations in the most oceanic area (A11, B11, and C11) presented biomass values 3 times lower than the mean value of their respective transects, highlighting a clear decrease of the biomass beyond the shelf. The mesozooplankton community was dominated by copepods, particularly by large- and medium-size calanoids and small Oithonidae. Large numbers of different copepodites stages and nauplii were found, as well as exuviae, indicating that individuals were in active growing phase over the whole area. Euphausiids, chaetognaths, appendicularians, amphipods, polychaetes, ostracods and
salps were found as well.