Zooplankton diversity and its relationship with environmental changes after the filling of a temporary saline lake in the semi-arid region of La Pampa, Argentina
Temporary water bodies can remain active as such for varying periods. However, they are reservoirs (as "egg banks") of species adapted to these special conditions. In central Argentina, there are numerous temporary lakes, which have only recently begun to be studied. The aim of this work was to describe the succession of changes in diversity, abundance and biomass of zooplankton as well as in the environment, over a period of eleven months, as from the filling of a temporary saline lake, and test the hypothesis that i) salinity affects negatively the richness and abundance but positively the biomass, and ii) due to changes in environmental conditions produced by advancing the hydroperiod, different species emerge from the egg bank at different times. At the beginning, when salinity was reduced and the concentration of chlorophyll-α was higher, we recorded the highest diversity, due mainly by less tolerance species. Later, as salinity increased, the macrophyta Ruppia cirrhosa developed and covered 90% of the surface of the lake, the concentration of chlorophyll-α decreased and the water transparency increased. The zooplankton richness decreased and the community was integrated only by halotolerant species. In the first two months, there was an increased replacement of species, indicated by the high value of Whittaker's beta diversity index (0.63), the density was high, with a predominance of microzooplankton, so the registered biomass was relatively reduced. Then, abundance decreased markedly, and was mostly dominated by macrozooplankton, so the biomass increased. When salinity exceeded 11 g L-1, there was a predominance of the halophilic cladoceran Daphnia menucoensis, a species of ecological importance because it's high grazing pressure on phytoplankton. In this study, in addition to the modulating effect of salinity on the richness, abundance and zooplankton biomass, it was verified that the diversity present in the egg bank of temporary saline lakes is higher than that recorded in the water column at any time during hydrophases.