Zooplankton ecology in high-mountain lakes

Abstract

Anthropogenic stress and fish introduction generally are thought to have eliminated vulnerable and sensitive zooplankton species from many alpine lakes, creating impoverished communities. To investigate this hypothesis we sampled 26 alpine lakes (1618 – 2757 m a.s.l.), 11 of which were studied in the early 20th century, and compared past and present zooplankton composition and taxa richness. We also studied how human induced changes may influence genetic diversity of present-day populations of the widespread cladoceran, Daphnia. Resampling did not show a drastic overall change in planktonic crustacean composition. Taxa richness significantly decreased with increasing lake altitude, but no other environmental factor correlated with richness. Large-bodied zooplankton taxa were found in lakes both with and without fish. Therefore we conclude that the presence of fish can be excluded as the general factor explaining the occurrence or absence of large zooplankton species in alpine lakes. Levels of chlorophyll a and POC best distinguished lakes with Daphnia from lakes without Daphnia. In 8 out of 12 lakes sexual Daphnia were more abundant than asexual individuals. Clonal diversity ranged from 0.01 to 1.3 but was not related to the proportion of sexual individuals. The ability to create resting stages may be an essential factor for the maintenance of genetic diversity and the long-term persistence of Daphnia and other zooplankton taxa.