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The distribution of zooplankton in the upper 100 m of the Mallorca channel (Balearic Sea) was investigated during the spring of 2001 and related to the main hydrographic parameters. Synoptic satellite images were examined and 29 stations were sampled by means of oblique hauls. The sea surface temperature, salinity, and chlorophyll a in the channel show the existence of a hydrological front related to the composition of phyto- and zooplankton. The main zooplankton groups revealed a horizontal distribution pattern related to the hydrographic features of the area. The highest zooplankton abundance, mainly due to copepods (78% of the total zooplankton), was found where the coolest and more saline waters were observed, i.e. in the northern part of the channel. The lowest abundance, mainly represented by siphonophores, chaetognaths, and doliolids, was in the south in the warmer and less saline waters, indicating the input of Atlantic waters into the channel. The spatial distribution of the main species and zooplankton groups was also examined in relation to the frontal system, suggesting their function as biological indicators of the upper water hydrography in the Balearic Sea (Western Mediterranean).

Abstract. In the western Mediterranean Sea, the RADMED monitoring programme is already conducting several of the evaluations required under the Marine Strategy Framework Directive (MFSD) along the Spanish Mediterranean coast. The different aspects of the ecosystem that are regularly sampled under this monitoring programme are the physical environment and the chemical and biological variables of the water column, together with the planktonic communities, biomass and structure. Moreover, determinations of some anthropogenic stressors on the marine environment, such as contaminants and microplastics, are under development.Data are managed and stored at the Instituto Español de Oceanografía (IEO) Data Centre that works under the SeaDataNet infrastructure, and are also stored in the IBAMar database. In combination with remote sensing data, they are used to address open questions on the ecosystems in the western Mediterranean Sea.