Studies on the functional role of tintinnids in the Southern California Bight. I. Grazing and growth rates in laboratory cultures

Five species of tintinnids, Amphorella quadrilineata (Claparède and Lachmann, 1858), Tintinnopsis cf. beroidea Stein (1867), T. cf. acuminata Daday (1887), Eutintinnus pectinis (Kofoid and Campbell, 1929), and Helicostomella subulata (Ehrenberg, 1833), were isolated from Southern California coastal waters and maintained in laboratory cultures which were used to investigate, several aspects of the feeding dynamics and population growth rates of this group of planktonic ciliates. Data are most complete for the latter three species. Both E. pectinis and H. subulata displayed ingestion and growth rates which increased with increasing food concentration until a maximum rate was obtained which then remained essentially constant as food levels increased further. Maximum hourly ingestion was equivalent to approximately 10 to 20% of the body weight of the tintinnids. T. cf. acuminata showed no such maximum ingestion rate, as ingestion rates increased throughout the entire range of food concentrations used. The dependence of growth rate of T. cf. acuminata on food concentration also differed from the other species, being characterized by a broad region of maximum growth at intermediate food levels with reduced growth at both lower and higher food concentrations. Maximum observed growth rates represented doubling times of approximately 12 h for both E. pectinis and T. cf. acuminata and 24 h for H. subulata. The data suggested gross growth efficiencies exceeding 50% over much of the range of food concentrations used. No strong evidence supporting the existence of feeding thresholds or switching behavior was collected during these experiments, although apparently selective feeding was observed in one experiment with E. pectinis.