Abstract:Effects of differentiation of microalgal species and concentrations on the feeding and digestive enzyme activities of marine planktonic copepod Calanus sinicus, the key species of Yellow Sea and East China Sea, were studied by the batch culture feeding experiment under controlled laboratory conditions, and three species of marine bait microalgae: Isochrysis galbana, Phaeodactylum tricornutum, and Paviova viridis were used in this experiment. Results showed that different microalgal species and concentrations had significant effects on the feeding of C. sinicus. (1) The critical food concentration of the tested bait microalga was the key point in deciding the change of ingestion rates (IR) of C. sinicus. IR increased steadily with the microalgal concentration increasing when it was below the critical concentration, but decreased obviously when it was above the critical concentration. The maximum IR on I. galbana, P. tricornutum, and P. viridis were 4664, 6021cells ml-1, and 4524 cells ml-1, respectively. Differently, clearance rates (CR) decrease monotonically with microalgal concentration increasing during the whole experiment. (2) The digestive enzyme activities of C. sinicus changed according to the micrialgal species and concentration variation, and the change to what extent was decided by the microalgal concentration. The activity of laminarinase was higher than that of maltase and cellobiase, and cellobiase had the relatively lower activity compared to the other two in the present study. Result also showed that microalgal species played an immportant role in affecting the digestive enzyme activities. C. sinicus fed with P. viridis had relatively higher digestive enzyme activities comapred with those fed with I. Galbana and P. tricornutum, although all the changes were not reached significance (P>0.05), suggesting the complexity and variability of zooplankton feeding in response to different diets. Further study of a particular alga-herbivore system can provide the fundamental information to clarify the substance cycle and energy flow in marine ecosystems.