Effects of water salinization and substrata quality on the performance of the shredder Schizopelex festiva (Trichoptera; Sericostomatidae)

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Abstract Secondary salinization is a growing concern for freshwaters worldwide. The lethal and sub-lethal effects on shredders are known, but not whether these result from direct exposure to contaminated aquatic medium and/or from indirect effects of distinct substrate quality through fungal conditioning in salinized media. Here, chestnut and oak leaves were conditioned for 4 weeks in reference (Cond0, 0 g/l NaCl) or salinized (Cond3, 3 g/l NaCl) media before being offered to the shredder Schizopelex festiva maintained in reference (Inv0) or salinized (Inv3) media. Fungal biomasses associated with leaf litter and consumption, respiration rates, growth, survival, and feeding preference of S. festiva were assessed. We found lower fungal biomass in both leaf species conditioned in Cond3 medium. Consumption rates were higher for oak than chestnut, and in Inv0 than Inv3, but were not affected by conditioning media. Growth was also affected by invertebrate media (Inv0 > Inv3), while Inv3 led to the lowest survival. Schizopelex festiva preferred Cond0 over Cond3 oak leaves only in Inv0. Results strongly suggest that direct exposure to salinized media is a main pathway of salt toxicity to shredders through a generalized reduction in invertebrates’ metabolic rates when facing salt stress. Salt addition to the media may result in an energetic investment in osmotic regulation at the expense of consumption and growth, with consequences for invertebrate survival. Potential negative effects of salt contamination on shredders’ ability to select more nutritious food items may contribute to cascading effects throughout the stream food webs, particularly in streams lined with more recalcitrant leaf litter.

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