EFFECTS OF DIET AND STARVATION ON DIGESTIVE ENZYME-ACTIVITY AND FEEDING-BEHAVIOR OF THE MARINE COPEPOD CALANUS-PACIFICUS

In this paper we look at the response of Calanus pacificus over a period of several weeks to both starvation and diet as reflected by survival rates, feeding rates and digestive enzyme activities. Phytoplankton species used as food were the diatom Thalassiosira weissflogii, two dinoflagellates, Gymnodinium simplex and Scrippsiella trochoidea, and the chlorophyte Dunaliella tertiolecta. In general, C.pacificus appeared to be resistant to starvation for periods up to 1 week. Survival remained high for at least 6 days of starvation, while maximum feeding rates remained constant for several days and then declined by 50% after a week of starvation. When initial digestive enzyme activities were low, they did not change appreciably during the experiments. However, activity levels dropped rapidly during starvation experiments in which they were initially high. Other evidence indicates that starvation may induce changes in the digestive system before it affects ingestion rates or survival. In general, long-term changes in digestive enzyme activity under different dietary regimes were gradual. An exception to this pattern was S. trochoidea, whose presence in the diet induced a precipitous, though reversible, decline in digestive enzyme activity, a phenomena possibly related to the toxic reaction to this species reported by other researchers. A positive induction of digestive enzymes occurred over a time-scale of 1-5 days in response to a change in diet. The absence of laminarin in the diet of C.pacificus for nearly 3 weeks (when feeding on G.simplex), during which time laminarinase activity declined by ̃50%, did not adversely affect subsequent assimilation of a laminarin-rich food (T. weissflogii). © 1990 Oxford University Press.