The effects of wind and diel vertical migrations on the distribution of freshwater Zooplankton

Abstract

A 24 hr survey of the behaviour of the Zooplankton in a shallow (approximately 1 m), eutrophic pond showed that both vertical distribution and abundance‐changes at the sampling site reflect several interacting factors, i.e., windforce and direction, local depth, diel vertical migrations, swimming capabilities of the animals, illumination, and, probably, “avoidance of shore”; reactions. Small zooplankters, lacking strong powers of locomotion (i.e., Rotifera, Copepoda nauplii) exhibit similar features: their distribution is rather homogeneous through time and space, and is chiefly conditioned by wind. Larger plankters ‐ such as adult copepods and cladocerans ‐ tend to concentrate at different depths during a 24 hr cycle; as a consequence differential horizontal currents displace varying proportions of their populations at different times, thus either concentrating the organisms at a given area, or carrying them away from it. This variability suggests that the influence of the factors mentioned on the estimates of zooplanktonic abundance and biomass ‐ based on samples collected under different conditions ‐ must be thoroughly evaluated when carrying out ecological investigations.