The pELAstics Project: Using in-field intermittent-flow respirometry to assess Yellow Perch metabolic rates after in-lake mesocosm exposures

The concentration of microplastics (MPs) is steadily increasing in freshwater ecosystems due to continuous inputs, fragmentation of larger particles, and their persistence in the environment. Still, the threat posed by MPs at environmentally relevant exposures to aquatic organisms remains unclear. Sublethal effects on fish metabolism have major implications for lifetime allocation to other biological functions such as growth and reproduction, which in turn can alter population and ecosystem stability. To address this knowledge gap, we conducted two in-lake mesocosm experiments in 2021 and 2022 to evaluate the effect of environmentally relevant microplastic concentrations on Yellow Perch (Perca flavescens) metabolic rates. For 10 weeks in 2021, Yellow Perch were exposed to a gradient of nominal MP concentrations ranging from 0 particles/L (two control mesocosms) to 29,240 particles/L (seven chemical additive mesocosms). For nine weeks in 2022, Yellow Perch were exposed to 0 particles/L (three control) and 29,240 particles/L (three with chemical additives and three additive-free). Standard and maximum metabolic rates (SMR; MMR) were measured using in-field intermittent-flow respirometry, and aerobic scope (AS) was calculated. Our findings from 2021 revealed no significant differences in mean mass-specific or mass-relative metabolic rates across treatments. While results from the 2022 experiment showed no significant differences in mean mass-specific metabolic rates, the slope of mass-relative SMR and MMR with body mass was greater in Yellow Perch exposed to MPs with chemical additives when compared to the control. By contrast, no significant differences were observed in the additive-free treatment compared to the control. These results underscore the importance of considering chemical additives when evaluating the sub-lethal effects of MPs on freshwater ecosystems, as well as the importance of replication in large mesocosm experimental designs. Also see: https://micro2024.sciencesconf.org/556971/document