Effects of 17α-ethinylestradiol on individual life-history parameters and estimated population growth rates of the freshwater gastropods Radix balthica and Bithynia tentaculata

Studies of aquatic environments exposed to 17α-ethinylestradiol (EE2) have demonstrated detrimental effects on fish communities. However, much less is known about effects on macro-invertebrates and especially how long-term exposure may affect critical life stages and ultimately population dynamics. We studied the effects of EE2 on relevant endpoints for population growth in two common freshwater gastropods, Radix balthica and Bithynia tentaculata , that differ in reproductive, foraging and anti-predator strategies and endocrine systems. We quantified critical life-history parameters (mortality, somatic growth rate, days to and size at first reproduction, egg production and hatching success) in a concentration–response, life cycle experiment. The two species responded to EE2 exposure in different ways, B. tentaculata showing a significantly lower somatic growth rate and R. balthica a higher somatic growth rate. However, the magnitudes of the effects were small and EE2 exposure did not have any significant effect on estimated population growth rates for the two snail species. The significant effects of EE2 on individual endpoints, but not on population growth rate for both species, emphasise the importance of evaluating higher level effects from long-term exposure studies.