Complex homes, complex lives: how macrophyte structural complexity shapes taxonomic and functional diversity in periphytic ciliate communities

Abstract Freshwater ecosystems, although representing less than 1% of Earth’s surface, are biodiversity hot spots whose supports ecosystem functions. In these systems, environmental heterogeneity, driven by habitat structural complexity, is recognized as a key factor shaping community structure. This study evaluated how structural complexity of four aquatic macrophytes influences the taxonomic and functional attributes of periphytic ciliate communities. Macrophytes were categorized using the macrophyte complexity index: Nymphaea amazonum , Cabomba furcata and Egeria najas (intermediate), and Utricularia foliosa (most complex). Richness and density tended to be higher in the most complex macrophytes, although significant differences emerged between the least and most complex species. For functional metrics, only functional richness showed differentiation among plants, increasing along the complexity gradient. Both taxonomic and functional composition varied among ciliate communities in different macrophytes, notably between the least and most complex species. RLQ analysis revealed segregation among macrophytes, with specific traits associated with particular plants. However, the weak differences found between the least and intermediate complexity suggest that increasing structural complexity does not necessarily mean an increase in overall heterogeneity. Instead, fine-scale microhabitat features (interstitial spaces, roughness and protrusions) appear to play a key role.