Feeding Behavior Responses of the Small Copepod, , to Toxic Algae at Different Concentrations.

The feeding relationship between copepods and phytoplankton has immense ecological significance. This study investigated the feeding behavior of copepods by studying the feeding selectivity of , a key small copepod species, using a high-speed camera. The feeding behavior of separately fed on three algae, , and , was studied at five different concentrations. The factors characterizing feeding behavior, including the beating frequency (BF), beating time (BT), and rejection behavior, were analyzed. The average BT and BF of fed on toxic algae were significantly lower than those of copepods fed on nontoxic algae, indicating that the toxic algae negatively affected their feeding behavior. There were no significant differences in feed rejection among the three algae during the short period of experimentation, indicating that the rejection behavior was insignificant in the early period (within 20 min) of feeding on toxic algae. The feeding behavior was inhibited when the concentration reached 250 cells/mL. The BT was initially affected at increasing concentrations followed by the BF, and and . reduced the BF at concentrations of 250 and 1000 cells/mL, respectively. Analysis of the average BFs revealed that was more significantly affected by containing diarrheal shellfish poison than by . containing paralytic shellfish poison. The BF of copepods fed on was significantly lower than that of copepods fed on . at 250-500 cells/mL but was not significantly different from that at 1000 cells/mL. This indicated that the inhibitory effect of on the feeding behavior was more significant at concentrations observed at the onset of red tide blooms (0.25-0.5 × 10 cells/mL), but insignificant at concentrations reaching those in advanced red tides (>10 cells/mL). This study demonstrates that toxic dinoflagellates alter the feeding behavior of copepods and describes the variations in their feeding response to different algal species and concentrations. The findings provide crucial insights for further studies on the feeding relationship between copepods and phytoplankton and on functional assessment of plankton ecosystems.