Grazing rate of the tintinnid Stenosemella ventricosa (Clap. & Lachm.) Jorg. on the spectrum of the naturally occurring particulate matter from a Mediterranean neritic area1

Stenosemella ventricosa, a Mediterranean neritic tintinnid, is a consumer of nanoplankton. It feeds on particles with diameters from 1.3 to 27 µm and more intensively on particles in the 3–12-µm range. After being acclimated for 24 h without food, S. ventricosa exhibits a very high feeding rate on a population of natural particles during the first few hours: 4 × 105 µm3 (wet vol food)·tintinnid−1·d−1. The rate decreases at about 20 h and stabilizes around a mean value of 4.6 × 104 µm3. The stabilized rate is equal to 66% of the fresh weight of the tintinnid (7 × 104 µm3), or 43% (0.0024 µg C·tintinnid−1·d1) of its body organic carbon (about 0.0056 µg). The ingestion rate of S. ventricosa feeding on particles between 1.3 and 27 µm seems to be a function of particle concentration. Significant correlations (at 0.01 or 0.05 level) were observed between ingestion rate per size class and particulate food concentration within each class. After feeding in some size range for a certain period, S. ventricosa seems to be able to switch its feeding pressure to particles in other size categories which have not yet been consumed.