Feeding selectivities and food niche separation of Acartia clausi, Penilia avirostris (Crustacea) and Doliolum denticulatum (Thaliacea) in Blanes Bay (Catalan Sea, NW Mediterranean)

Selectivity-size spectra, clearance and ingestion rates andassimilation efficiencies of Acartia clausi (Copepoda), Peniliaavirostris (Cladocera) and Doliolum denticulatum (Doliolida)from Blanes Bay (Catalan Sea, NW Mediterranean) were evaluatedin grazing experiments over a wide range of food concentrations(0.02–8.8 mm³ L^–1 plankton assemblages from BlanesBay, grown in mesocosms at different nutrient levels). Acartiaclausi reached the highest grazing coefficients for large algae>70 µm (longest linear extension), P. avirostris forintermediate food sizes between 15 and 70 µm, and D. denticulatumfor small sizes from 2.5 to 15 µm. Penilia avirostrisand D. denticulatum acted as passive filter-feeders. Acartiaclausi gave some evidence for a supplementary raptorial feedingmode. Effective food concentration (EFC) decreased linearlywith increasing nutrient enrichment for D. denticulatum andfollowed domed curves for A. clausi and for P. avirostris withmaximum values at intermediate and high enrichment levels, respectively.Clearance rates of crustacean species showed curvilinear responseswith narrow modal ranges to increasing food concentration. Clearancerates of D. denticulatum increased abruptly and levelled intoa plateau at low food concentrations. Mean clearance rates were13.9, 25.5 and 64.1 mL ind.^–1 day^–1, respectively.No clearance could be detected for A. clausi at food concentrations<0.1 mm³ L^–1 and for P. avirostris at food concentrations