Number of drifting and emerging invertebrates under control and predator exposure conditions in an outdoor mesocosm experiment

Predator-prey interactions drive adaptation in aquatic communities, shaping invertebrate behaviour. In response to predation risk, invertebrates may exhibit behavioral changes, such as drifting with the downstream current or altering the timing of emergence to avoid predators. To investigate predator-induced drift behaviour and emergence patterns, we collected drifting and emerging invertebrates from an outdoor mesocosm system (ExStream system) between March and April 2022. The study examined the effects of indirect and direct predation pressure on drift and emergence by recording the number, lowest possible taxonomic resolution, and size of invertebrates. Drift nets attached to the outflow and emergence nets placed over the mesocosms were collected every 24 hours at 4 PM over nine days. Mesocosms were maintained under either control or predator exposure conditions. In the predator exposure treatment, invertebrates were first exposed to elevated chemical cues from fish (Gasterosteus aculeatus and Cottus rhenanus) to simulate indirect predation. On the fifth day after sampling, one Cottus rhenanus was introduced into each predator-treated mesocosm to simulate direct predation.