Assessing the effect of food and light on Calanus sinicus swimming behavior through video-recording experiments

The copepod Calanus sinicus is a common and abundant species in the shelf waters of the western North Pacific from Japan to Vietnam, and is a main food source for crucial fish species. This study examined the effect of food and light on the swimming behavior of this species. The swimming activity was assessed by using 2 approaches that focused on the dynamics of swimming states and the statistical properties of their trajectories. We discovered that the complexity of swimming paths was reduced under illuminated conditions, and intensified in the absence of food. The swimming activity in such conditions was characterized by a less tortuous shape of trajectories, a lower instantaneous swimming velocity, and a lower recurrence of extreme events. In addition, the entropy of swimming paths decreased when food was included, and the minimal entropy was reached in dark conditions and presence of food, indicating predictable behavior. A general increase in swimming activity was dominated by the slow swimming state. The variations in the swimming activity of adult females exhibited an adaptive pattern that allowed maximizing the exploitation of the three-dimensional, and generally diluted environment that the copepods inhabit, as well as limiting the risk of the predation. (C) 2012 Published by Elsevier B.V.