Feeding behavior responses of Paracalanus parvus and Calanus sinicus to three typical HABs algae at different concentrations

This study investigated the feeding behaviors of two copepods, Paracalanus parvus and Calanus sinicus on three algae species ( Heterosigma akashiwo , Prorocentrum micans , and Skeletonema costatum ). High-speed cameras were used to record feeding behaviors and metrics including beating frequency (BF), beating time (BT), and rejection behavior. The results showed that the average BF and BT of P. parvus were significantly higher than those of C. sinicus , indicating that P. parvus displayed more active feeding behavior. In addition, the average BF of P. parvus fed diatoms was significantly higher than that of others, exhibiting a stronger top-down control of P. parvus over diatoms. Further analysis on the algae at different concentrations revealed that when P. parvus was fed on H. akashiwo , the average BT exhibited an initial increase followed by a decrease, and when fed P. micans , the average BF exhibited a significant decrease, however, when feeding on S. costatum , neither of two species of copepods showed a significant trend with increasing algal concentration. These results further verify that P. parvus exhibits stronger feeding control on diatom, comparatively, C. sinicus was not influenced by increasing algal concentration. This study clarifies the strong control ability of small copepods and provides evidence for the analysis of top-down control. • High-speed camera can directly analyze copepod feeding activity through behavioral characteristics. • Small copepods have higher feeding activity. • Paracalanus parvus has stronger control capability over diatoms. • Increasing HABs algae concentration inhibits copepod feeding behavior.