Lagrangian modelling of swimming behaviour and encounter success in co-occurring copepods: Clausocalanus furcatus vs. Oithona plumifera

The calanoid Clausocalanus furcatus and the cyclopoid Oithona plumifera are species dominating the copepod assemblage in oligotrophic environments but displaying contrasting swimming behaviour. C. furcatus moves almost continuously along very convoluted trajectories, while O. plumifera sinks slowly with occasional brief relocating jumps. To evaluate the efficiency of such opposing behaviour in encountering potential prey, the swimming performances of both species are here simulated with a Lagrangian, individual-based approach, implemented to simulate the realistic motion and perceptive fields of the two species. For each modelled swimming trajectory, we calculate the number of realised encounters and the associated search efficiency in uniform and patchy distributions of virtual prey. C. furcatus will perform better than O. plumifera in terms of realised encounters, but its search efficiency will be lower owing to the peculiar motion behaviour and to the shape and extension of the perceptive field. Despite these differences, these two species do co-exist in food diluted areas, thus indicating alternative strategies to successfully thrive in pelagic oligotrophic environments.