Long-term individual and population effects of multiple stressors, using a model freshwater mollusc (Lymnaea stagnalis)

Human activities are driving biodiversity loss by increasing the exposure to multiple environmental stressors with pollution, climate change and invasive species being amongst the most important contributors. Here, we used the pond snail, Lymnaea stagnalis, as a model organism to investigate the combined effects of an environmentally relevant pollutant mixture, temperature increase and an invasive predator cue on physiological endpoints and behaviour. Dose-response data from single stressor exposures gathered over the partial life-cycle exposure period were used to calculate effect concentrations (EC10 and EC30) and responses to their combinations were investigated. At the EC30 for temperature (20 °C vs. 22 °C), effects were widely observed. While growth and reproduction were stimulated, this modest temperature increase negatively impacted survival (20 % reduction). Neither the pollutant mixture nor the predator cue severely impacted the examined responses and did not exacerbate the temperature effects. By contrast, the application of all three stressors at the EC30 level tended to ameliorate stress, compared to the temperature EC30 alone. Exploratory analyses also revealed that snails that avoided the predator cue by moving above the water line exhibited higher growth than those that remained in the water. Our results indicate that a number of organismal trade-offs may be occurring, such as between survival and reproduction, highlighting the complexities of predicting the impact of multiple stressors. Finally, the pronounced effects observed in response to this temperature increase (+2°C) is concerning, as this is within currently observed planetary warming, with organisms inhabiting small water bodies particularly susceptible due to their small water volumes.