Beyond taxonomy: A functional approach reveals patterns of reef fish response to wastewater pollution

Coral reefs face severe threats from climate change and local stressors like wastewater pollution, which significantly impact reef ecosystems but remain underexplored. Reef fish are essential for supporting human livelihoods through fisheries and maintaining ecosystem functions such as nutrient cycling and algae control. While most research focuses on wastewater's effects on benthic communities, its impact on reef fish physiology, behavior, and community structure is poorly understood. Few studies apply trait-based approaches to evaluate wastewater's influence on fish's ecological roles. This study systematically reviews 52 papers and conducts a meta-analysis of eight control-impact studies to assess wastewater effects on reef fish taxonomic and functional structure. Taxonomy-based metrics revealed mixed responses, with studies reporting declines, increases, or no changes in abundance, richness, and biomass in polluted sites. Functional analysis provided clearer patterns: polluted sites were dominated by smaller, high-resilience species at mid-trophic levels, while control sites supported larger, low-resilience species at diverse depths and trophic levels. Functional richness was generally higher in control sites. Pollutant-specific effects varied: sediments impaired feeding efficiency and growth, while nutrient enrichment shifted species composition by favoring lower trophic levels. These findings demonstrate the limitations of taxonomy-based metrics and highlight the value of functional approaches for detecting early ecosystem degradation. Integrating functional ecology with wastewater characterization enhances predictions of ecological responses and supports targeted management strategies. This research emphasizes the urgency of addressing wastewater pollution to safeguard reef biodiversity and ecosystem services critical to human well-being.