MEPS 168:119-126 (1998)  -  doi:10.3354/meps168119

ABSTRACT: Three small, neritic copepods (Acartia tonsa, Acartia clausi, and Centropages hamatus) were exposed to short term (1 to 14 h) periods without food and their clearance over 2 h was measured. Clearance rates in controls consisting of copepods continuously exposed to 3500 cells ml^-1 of the diatom Thalassiosira weissflogii were 1.15 ml µg^-1 dry wt d^-1 for A. tonsa, 0.65 for A. clausi and 0.35 for C. hamatus. When moved from filtered sea water to a suspension of 3500 T. weissflogii ml^-1, A. tonsa showed elevated (compared to controls) clearance rates after having been deprived of food for 6 h (+77%) and 14 h (+44%). A. clausi only responded after 14 h of starvation (+60%) whereas C. hamatus showed a moderate response after 6 h without food (+14%). In day-night comparisons with A. tonsa, elevated clearance rates were significantly higher only during the day. Frequent estimates of clearance rates (20 min intervals) showed that the stimulating effect of food deprivation only lasted ~1 h in the case of 1 h of starvation but lasted more than 3 h after 14 h without food. Small species like the ones investigated here have more restricted vertical migration and may not leave the food-rich surface layer to avoid predation, as is commonly found in larger copepods. Instead, they have to balance food intake with predator avoidance continuously. The hunger responses observed in the study may allow the copepods to intermittently search for food or avoid predators and still maintain the same overall ingestion rate as constantly feeding animals.

KEY WORDS: Acartia tonsa · Acartia clausi · Centropages hamatus · Clearance rates · Hunger responses