Individual and combined effects of shading and habitat complexity on benthic macroinvertebrate communities in a mesocosm stream experiment (São Paulo, Brazil)

Abstract Introduction Agricultural activities are a major driver of biodiversity loss and ecosystem degradation in subtropical streams, often altering macroinvertebrate community structure and associated ecosystem functions. Although restoration strategies increasingly target these impacts, the relative importance of riparian shading and in‐stream habitat complexity remains poorly understood. Objectives This study evaluated the individual and combined effects of shading and habitat complexity on macroinvertebrate recolonization, aiming to inform ecological restoration strategies in agricultural landscapes. Methods We conducted a 42‐day mesocosm experiment under controlled conditions. Forty‐eight mesocosms were exposed to three shading levels (0, 30, and 70%), with or without the addition of rocks and branches to increase habitat complexity. Macroinvertebrate communities were assessed using abundance, taxa richness, Shannon diversity, equitability, and EPT richness and abundance indices. Results Shading significantly increased macroinvertebrate abundance and diversity, whereas habitat complexity enhanced abundance, with no significant effects on richness or diversity indices. The combination of 70% shading and increased structural complexity resulted in the highest macroinvertebrate abundance. Overall, shading exerted a stronger influence on community responses than habitat complexity applied alone. Conclusion These results highlight the importance of shading and habitat complexity in enhancing macroinvertebrate community structure, although their effects on taxonomic diversity appear limited. Shading consistently promoted increases in abundance and diversity, while structural complexity primarily affected abundance, suggesting complementary but distinct ecological roles.