The swimming behavior of Daphnia magna ensemble in two-dimensional space from the diffusion motion point of view

Abstract

Locomotion and dispersal are important processes that affect the distribution and abundance of organisms in aquatic environment. In this study we observed the movement of a group of Daphnia magna called an ensemble. In laboratory conditions, the distribution of fifty daphnids (in triplicate) at the release from the point source in two-dimensions was examined. In experiments, animals were placed in a square plastic container with thin layer of culture medium and the video of their movements was recorded. Video processing and measuring of swimming behaviour was carried out by the TrackTox software. Mathematical and statistical analyses were performed using the functions and packages of the R software. The diffusion motion equation used allowed to obtain the value of the diffusion coefficient, which in our case was 0.051+/-0.009 cm² s⁻¹. The approach used can be used to model the migration and spatial distribution of these microscopic crustaceans. Moreover, given the fact that certain parameters of swimming behavior are already used to toxicity assessment, the diffusion parameters of a Daphnia ensemble can also be proposed as a characteristic in ecotoxicological studies.