RATES OF INGESTION AND THEIR VARIABILITY BETWEEN INDIVIDUAL CALANOID COPEPODS - DIRECT OBSERVATIONS

The goals of this study were to determine rates of ingestion and fecal pellet release, and their variability, for individual planktonic cope pods over extended periods of time (>20 min). Ingestions and rejection s of individual cells of the diatom Thalassiosira eccentrica by adult females of the calanoid Paracalanus aculeatus were directly quantified by observing individual copepods continuously at cell concentrations ranging from 0.1 to 1.2 mm(3) 1(-1). Average ingestion rates increased with increasing food concentration, but were not significantly differ ent between 0.3 and 1.0 mm) 1(-1) (9.8 and 32.7 mu g C 1(-1)) of T. ec centrica. Rates of cell rejections were low and similar at 0.1 and 0.3 , but were significantly higher at 1.0 mm(3) 1(-1). The coefficients o f variation for average ingestion rates of individual copepods hardly differed between food concentrations, ranging from 17 to 22%, and were close to those for average fecal pellet release intervals which range d from 15 to 21%. A comparison between individuals at each food concen tration found no significant differences at 1.0; at 0.1 and 0.3 mm(3) 1(-1), respectively, ingestion rates of four out of five females did n ot differ significantly from each other. Average intervals between fec al pellet releases were similar at 0.3 and 1.0 mm(3) 1(-1) of T, eccen trica, but significantly longer at 0.1 mm(3) 1(-1). Fecal pellet relea se intervals between individuals were significantly different at each food concentration; these significant differences were attributed to r ather narrow ranges of pellet release intervals of each individual fem ale. Potential sources/causes of variability in the sizes and rates of copepods in the ocean are evaluated.