Studies on the functional role of tintinnids in the Southern California Bight. III. Grazing impact of natural assemblages

Abstract

Tintinnids were identified and enumerated in samples from 100 stations in the Southern California Bight. Spring and summer samples were collected at weekly intervals at 3 locations off La Jolla, California (USA) in 1967. Samples were also taken at considerably wider spatial and temporal intervals during 4 cruises in the fall and winter of 1974–1975. Ninety-one species of tintinnids were identified, comprising assemblages ranging in density to over 18x10⁶ tintinnids m^-3. Previously published accounts of the feeding rates and behavior of tintinnids were then applied to this tintinnid assemblage in order to estimate their impact on the flow of carbon through the planktonic food web. Generally, for both surveys, less than 4% of the daily primary production was consumed by the observed tintinnid stocks, although at 14 stations calculated ingestion by tintinnids exceeded 10% and at 4 stations it exceeded 20% of the measured daily primary production. Other ciliates in the 1967 samples were, combined, approximately as abundant as the tintinnids; if their grazing rates were comparable, the consumption by the total ciliate assemblage would be double that of the tintinnids alone. The high tintinnid growth efficiencies previously observed (Heinbokel, 1978a) and the relatively high efficiency with which tintinnids can be grazed by larger consumers suggest that relatively little of the energy and material fixed by the nanno-phytoplankton may be lost to the larger consumers by the insertion of a ciliate “extra link” into the food chain.