Changes in the mesozooplankton community associated with the hydrography off the northwestern Iberian Peninsula

Abstract

Abstract Changes in the mesozooplankton community were investigated along the northwestern coast of the Iberian Peninsula during OMEX II cruises in August 1998, under upwelling conditions, and in October 1999, when there was a saline, warm poleward current flowing along the slope. Six stations, located at both the shelf break and in oceanic waters, were sampled for mesozooplankton by day and by night. Samples were grouped in accordance with their species abundance levels, and the resulting groups were compared with salinity, integrated chlorophyll a, and sea surface and average temperatures. The analysis discriminated stations from different cruises into different groups, and detected the influence of hydrographic structures. The abundance of species linked to high concentrations of Chl a and low temperature increased during the upwelling session, whereas species related to warmer water were more abundant during the 1999 cruise. Further, the analysis revealed differences in the mesozooplankton composition between coastal and oceanic sites, which were influenced to different degrees by the upwelling and the poleward current.