Swimming behaviour of developmental stages of the calanoid copepod Temora longicornis at different food concentrations

The swimming behaviour of developmental stages of the marine calanoid copepod Temora longicornis was studied using 2-dimensional observations under a microscope and a 3-dimensional filming technique to analyze swimming mode, swimming speed and swimming trajectories under different food concentrations. The nauplii swam intermittently in a stop-and-go fashion. The swimming behaviour of the smallest feeding stage (N2) did not change with different food concentrations. The largest nauplius stages reacted to an increased food concentration by increasing the percentage of time spent swimming. All copepodid stages swam continuously their mouthparts moving nearly 100% of the time. Copepodids can therefore only increase their feeding effort by increasing their limb beat frequency. Adult females showed low swimming speeds at very low food concentrations, higher swimming speeds at intermediate concentrations and low swimming speeds at very high food concentrations. This agreed with expectations based on the optimal foraging theory. Males behaved differently from the females. Not only was the average swimming speed of males higher at similar food conditions, but they also maintained a very high swimming speed at very high food concentrations. This increased swimming activity in the males may be linked to a mate seeking strategy. Neither males nor females showed any obvious differences in turning behaviour at different food concentrations.