Seasonal spatial pattern and community structure of zooplankton in waters off the Baleares archipelago (Central Western Mediterranean)

•We portray micrometazooplankton and mesozooplankton communities at two fishing grounds around the Baleares islands (WM) during autumn and summer.•Micrometazooplankton dominated in the total metazooplankton abundance, represented mostly by nauplii and copepods.•Seasonal differences were depicted both in terms of standing stock and community composition.•Differences between areas varied seasonally and in dependence to hydrological features. Community composition showed dissimilarity between areas only in summer.•Our results reveal that the micrometazooplankton constitute a key food source for fish larvae in oligotrophic ecosystems.

We investigated the zooplankton community in two different areas of the Baleares Archipelago, Western Mediterranean, using data obtained in autumn (December 2009) and summer (July 2010). Micrometazooplankton and mesozooplankton samples were collected in the 0–200 m layer above the shelf (200 m) and the slope (900 m) of each area by a 53 μm and a 200 μm mesh size net respectively. The zooplankton biomass (expressed as dry weight) was higher in autumn than in summer (9.30 and 6.95 mg m− 3, respectively) with an important contribution of micrometazooplankters (29% and 41% of total biomass respectively). The latter fraction overwhelmed in the entire metazooplankton abundance, suggesting a non-negligible role as potential food for fish in the epipelagic waters of the Baleares archipelago. The abundance of micrometazooplankton was two-fold higher in December (3581 ind. m− 3) than in July (1585 ind. m− 3), represented mainly by small copepods and nauplii. Likewise, the mesozooplankton community showed smaller difference between months (554 and 390 ind. m− 3, in December and July). Micrometazooplankton abundance was higher in the northern area than in the southern area during autumn, probably linked to the presence of a front, while the opposite was found in summer. In both periods and areas copepods dominated, and within the highly diverse community ten species and their juveniles accounted for 70% of the community. In both areas, Clausocalanus (C. pergens + paululus and C. arcuicornis), Paracalanus parvus, Oncaea media, Oithona plumifera and Acartia clausi were abundant in autumn, whereas Centropages typicus, Temora stylifera and Mecynocera clausi were mainly present in summer. ANOSIM analysis revealed significant differences in the mesozooplankton community composition between months while differences between areas were detected only in summer.