The effects of suspended sediments on the swimming behavior of the calanoid copepod, Acartia tonsa

Abstract

Abstract Copepod swimming behavior is governed by chemical and hydro-mechanical cues. The environment of copepods, however, is frequently impacted by anthropogenic activities, in particular increased levels of suspended sediment due to coastal development. To better understand the effects of sediments on copepod behavior, we used video recordings to document free-swimming in Acartia tonsa under five sediment regimes, both with and without food. Results of the video analysis indicate that as sediment concentration increased, jumping increased and swimming paths became more convoluted. In the presence of prey, swimming trajectories became circular, as opposed to without prey, where paths were more erratic and slower. There was a reverse trend at higher sediment concentrations (120 and 200 mg l−1) for net velocity, turning rate and “spread of participation” index, which could indicate a behavioral threshold. Overall, greater motility with increasing sediment concentration suggests that the copepods were trying to transport themselves out of the sediment-affected area. In the absence of food, the energy cost of this behavior may affect the fitness of Acartia tonsa and, consequently, its predators.