Coral reefs are increasingly threatened by local stressors, yet the ecological consequences of wastewater pollution remain surprisingly poorly understood, particularly for reef fishes. While studies often focus on changes in species richness or abundance, these measures provide only a partial picture of how reef ecosystems respond to chronic pollution. This dissertation explores wastewater pollution through a functional perspective, asking how pollution reshapes reef fish communities by altering the ecological roles they perform and the mechanisms that underlie these changes.
Combining a meta-analysis, field studies along a wastewater pollution gradient in the Colombian Caribbean, and a controlled laboratory experiment, this work shows that wastewater consistently drives a reorganization of reef fish assemblages rather than a simple loss of biodiversity. Wastewater exposure was associated with changes in the occurrence of species with particular combinations of ecological traits and with a contraction of functional diversity. Yet some species occurred across both control and impacted environments, suggesting that differences in tolerance may play an important role in determining which fishes persist under wastewater-driven environmental change. Experimental results further showed that responses to potentially toxic wastewater components such as ammonia can be species-specific, providing a possible mechanism underlying the tolerance of some reef fishes to wastewater exposure.
Our findings show that wastewater can reshape reef fish assemblages through interconnected changes in environmental conditions, ecological functions, resource availability, and species-specific responses to physiological stress. Understanding why some species persist while others disappear is therefore important for anticipating how reef fish communities may reorganize under chronic wastewater exposure. By linking broad ecological patterns with species-level mechanisms, this dissertation provides a new framework for understanding and monitoring the effects of wastewater pollution on reef fishes.