Studies on the functional role of tintinnids in the Southern California Bight. II. Grazing rates of field populations

The feeding behavior of relatively undisturbed natural populations of tintinnids was studied in a series of experiments which utilized water samples collected in Southern California coastal waters. Dilute suspensions of corn starch were presented to the tintinnids and the rates of ingestion of this visual tracer determined after short (5 to 20 min) incubations followed by fixation in Lugol's iodine fixative. Tintinnids were observed to ingest particles of diameters up to approximately 43% of their lorica oral diameter and at rates proportional to their oral diameters. Grazing rates observed in these experiments ranged up to approximately 10 l tintinnid^-1 h^-1, and generally agreed well with the rates observed in experiments utilizing laboratory cultures of tintinnids. No significant diel periodicity in feeding rates was observed in the one study extending over a 24 h period.