Salinity shapes zooplankton community and functional diversity and has complex effects on size structure in lakes

Abstract

Changes in zooplankton community structureand function were analyzed in 24 lakes covering awide salinity gradient (from 0.5 to 115 g l-1) in asemiarid region in northwest China. We hypothesizedthat species richness (S), species diversity (H), functionaldiversity (FD), biomass, and size of zooplanktonwould decrease with increasing salinity. We found thatS, H, and FD did decrease with increasing salinity,whereas zooplankton sizes, size range, and biomassesdid not. In fact, the sizes of microcrustaceans weremainly regulated by the abundance of small fish.Besides the impoverishment of FD, the zooplanktonfunctional groups also varied along the salinitygradient. A shift occurred from selective raptorial tomore generalist microphagous rotifers, from selectiveto more generalist filter feeder cladocerans, and fromdominance of microphagous herbivorous copepods tomicrophagous carnivores. Our study indicates that theongoing salinization of lakes with climate warmingwill result in important changes in the zooplankton,affecting not only the structure but also the functioningof this community. A weakened top-down control byzooplankton on phytoplankton at moderate highsalinities may be an indirect consequence, leading toa worsening of eutrophication symptoms. Loss of fishat high salinities may, however, counteract this effect.