Detecting temporal and spatial trends of aquatic communities of subtropical and temperate ecosystems using multi-variate analyses

Aquatic ecosystems are undergoing rapid change due to climate pressures, habitat degradation, and human activity. Understanding how biological communities respond across different environments is crucial for conservation and management. This thesis applies a consistent multivariate analytical framework to explore patterns of community structure and change in a wide range of aquatic systems, spanning marine, coral reef, and freshwater environments. Using long-term and large-scale datasets, I analyzed spatial and temporal dynamics of fish and benthic communities across the Red Sea, the Mediterranean Sea, the Caribbean, and the freshwater river networks of Emilia-Romagna (Italy). Each chapter investigates different ecological gradients, such as protection status, land based human impact, and climate variability, while emphasizing the importance of community composition beyond traditional biodiversity metrics. Results reveal system-specific responses: temporal shifts, functional redundancy, resilience to disturbance, and species-level sensitivity to environmental change. Together, these studies demonstrate that community-level analyses can reveal ecological processes that may otherwise remain undetected through more traditional summary approaches. By integrating citizen science data, and long-term ecological monitoring, this work highlights the potential of multivariate tools to detect subtle but meaningful changes in aquatic communities. It contributes to both methodological development and applied ecology by offering scalable strategies for assessing ecosystem health across diverse aquatic contexts.