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ow nloaded from 2ABSTRACT Selectivity-size spectra, clearance and ingestion rates and assimilation efficiencies of Acartia clausi (Copepoda), Penilia avirostris (Cladocera) and Doliolum denticulatum (Doliolida) from Blanes Bay (Catalan Sea, NW Mediterranean) were evaluated in grazing experiments over a wide range of food concentrations (0.02 to 8.8 mm3 L-1 plankton assemblages from Blanes Bay, grown in mesocosms at different nutrient levels). Acartia clausi reached highest grazing coefficients for large algae>70 µm (longest linear extension), P. avirostris for intermediate food sizes between 15 and 70 µm, and D. denticulatum for small sizes from 2.5 to 15 µm. Penilia avirostris and D. denticulatum acted as passive filter-feeders. Acartia clausi gave some evidence for a supplementary raptorial feeding mode. Effective food concentration (EFC) decreased linearly with increasing nutrient enrichment for D. denticulatum and followed domed curves for A. clausi and for P. avirostris with maximum values at intermediate and high enrichment levels, respectively. Clearance rates of crustacean specie