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 overa period of several weeks to both starvation and diet as reflectedby survival rates, feeding rates and digestive enzyme activities.Phytoplankton species used as food were the diatom Thalassiosiraweissflogii, two dinoflagellates, Gymnodinium simplex and Scrippsiellatrochoidea, and the chlorophyte Dunaliella tertiolecta. In general,C.pacificus appeared to be resistant to starvation for periodsup to 1 week. Survival remained high for at least 6 days ofstarvation, while maximum feeding rates remained constant forseveral days and then declined by 50% after a week of starvation.When initial digestive enzyme activities were low, they didnot change appreciably during the experiments. However, activitylevels dropped rapidly during starvation experiments in whichthey were initially high. Other evidence indicates that starvationmay induce changes in the digestive system before it affectsingestion rates or survival. In general, long-term changes indigestive enzyme activity under different dietary regimes weregradual. An exception to this pattern was S. trochoidea, whosepresence in the diet induced a precipitous, though reversible,decline in digestive enzyme activity, a phenomena possibly relatedto the toxic reaction to this species reported by other researchers.A positive induction of digestive enzymes occurred over a time-scaleof 1–5 days in response to a change in diet. The absenceof laminarin in the diet of C.pacificus for nearly 3 weeks (whenfeeding on G.simplex), during which time laminarinase activitydeclined by {small tilde}50%, did not adversely affect subsequentassimilation of a laminarin-rich food (T. weissflogii).