Comparison of mesozooplankton assemblages across quasi-synoptic oceanographic features on the north-western Iberian shelf break

Abstract

The mesozooplankton community at the north-western Iberian shelf break was studied among adjacent oceanographic regimes (including upwelling, stratification and anticyclonic eddies) during 17 days in autumn 2009. Zooplankton sampling locations were determined in situ, after identifying the oceanographic regimes from CTD profiles performed over the continental shelf and upper slope. Zooplankton samples were sorted indentifying taxonomically the main zooplankton groups, from phylum to subclass. Copepods were the most abundant group (ind m−3) in all stations, followed by appendicularians, doliolids and siphonophores. The mesozooplankton community was significantly different amongst oceanographic conditions. Meroplankton abundance was higher in upwelling stations; particularly lamellibranchia, polychaeta and bryozoan larvae abundance, and decreased from early to late upwelling conditions. Medusae and chaetognata were found exclusively under the latter oceanographic regime. However, dissimilarity between the oceanographic conditions was mostly based on the varying contribution of the four most common groups.