Horizontal distribution of the rotifer plankton of Lake Aydat (France)

We investigated the causes of the shift which occurs in the horizontal distribution of planktonic rotifers of Lake Aydat. A normalised PCA was used to analyse the spatio-temporal distribution of 18 rotifer species. They are more numerous in the littoral zone, but seasonal changes remain higher than spatial changes. Results illustrate the capability of rotifers to take efficiently advantage of available space and food. The digestive tracts of fry and juvenile roach was also analysed and the index of Ivlev was used to determine prey selection. Fish predation occurs in the nearshore zone and the interactions between invertebrate predators and their prey are illustrated by the quantitative changes in community dynamics. Among the complex cascade of events varying in the course of the year, and despite of resource partitioning, predator-prey interactions as well as the exploitative competition between rotifers and crustaceans produce gradients exhibited in the horizontal distribution of rotifers in Lake Aydat.