Fish predation induces drifting and emergence in an experimental stream mesocosm system

Predator-prey interactions are important drivers of adaptation in aquatic communities, shaping the behaviour of invertebrates with cascading effects on community dynamics. Behavioural responses, such as moving with the downstream current (drift) or altering the timing of emergence, can be initiated and reduces the risk of encountering predators. This study aimed to examine the effects of indirect and direct predation pressure on drift behaviour and emergence patterns of aquatic invertebrates. Using an experimental mesocosm setup (ExStream), we analysed how the number of drifting and emerging invertebrates changed with elevated levels of chemical cues from fish (indirect predation, Gasterosteus aculeatus and Cottus rhenanus) and subsequent additional direct predation by Cottus rhenanus over a 9-day period. Our findings show that most of the analysed invertebrate groups displayed noticeable responses to either indirect, direct, or both forms of predation. Furthermore, our study revealed a significant impact of predation on emergence patterns, reducing the number and the size of emergent invertebrates. Given the importance of drift and emergence in dispersion and in facilitating resource flows into terrestrial systems, our findings indicate a strong effect of predation on the communities.