Warming masks the inhibitory effect of low concentration of cadmium on rotifer eliminating Phaeocystis population

The impact of heavy metal pollution on plankton in the context of climate warming may become more complex, especially on the population dynamics of zooplankton and algae. To address this important scientific issue, we studied the effect of heavy metal cadmium pollution (6 μM: environmentally relevant concentration; 12 μM: non-lethal concentration but causing negative effect on reproductive performance of rotifer Brachionus plicatilis) on the removal of harmful alga Phaeocystis globosa population by rotifer B. plicatilis under warming condition. Results showed that there was an interaction between temperature and cadmium on rotifers eliminating P. globosa population. Warming accelerated the removal of P. globosa population by rotifers under cadmium free and low cadmium conditions. Although the concentration of cadmium used was not lethal but reduced reproductive performance, it prevented rotifers from completely eliminating P. globosa population, indicating that cadmium had a significantly greater negative impact on rotifer population than on life history traits. The environmentally relevant concentration of cadmium delayed the removal of P. globosa population by rotifers at normal temperature, but this delay effect did not occur under high temperature conditions, indicating that warming completely masked the negative effects of environmentally relevant concentration of cadmium on rotifers eliminating P. globosa. The findings suggested that dual stress of warming and heavy metal pollution comprehensively impacted the top-down effect of zooplankton on algae, which may result in a substantial consequence on the population dynamics and energy flow between primary producers and primary consumers.