Effects of hunger and season on the feeding behavior of Calanus pacificus1

Abstract

Clearance rates were determined for starved and previously fed females of Calanus pacificus grazing on single sizes and mixtures of sizes of unicellular diatoms. Starved females fed at higher rates than previously fed animals, even at low food concentrations. In experiments with starved Calanus grazing on mixtures of sizes of diatoms, clearance rates increased progressively with increasing cell size and the clearance rate on any cell size was independent of the relative availability of that size. However, starved Calanus removed diatoms of different sizes from the water at different relative efficiencies from continuously feeding females. Because C. pacificus females migrate vertically and are undoubtedly accustomed to a diurnal variation in the availability of food, experiments incorporating a period of starvation may reflect more accurately their feeding behavior in the field. The observations were made in several seasons and include strong seasonal changes in the maximum clearance rate which appear to be associated with the timing of the spring bloom of phytoplankton in the main basin of Puget Sound.