Abstract:
Wastewater pollution and its impact on coral reef ecosystems have been a global concern for many years. Today, more than 25% of the world’s coral reefs are threatened by sewage contamination. In heavily disturbed areas, coral and reef fish populations decline sharply, often leading to a shift from coral-dominated to algae-dominated ecosystems. Such is the case for San Andrés, a tourism-dependent island whose ecosystems are increasingly affected by wastewater discharge.
Unfortunately, low-level disturbances are often difficult to detect or assess in time. Traditional methods, such as taxonomy-based indices, typically overlook the biological and functional differences among species, assuming that they are unrelated. In contrast, functional approaches have proven to be more sensitive, offering deeper insights by analyzing species traits. These traits encompass biological, physiological, and phenological characteristics measured at the individual level, which influence species performance and fitness.
In this context, we aimed to assess the direct and indirect impacts of wastewater on the functional structure of reef-fish communities, seeking to identify patterns or indicators of pollution. To do this, we conducted underwater visual censuses (UVC) to record fish abundances across seven sampling stations along the west coast of San Andrés Island. The stations were selected along a gradient of sewage pollution, based on their distance from a wastewater outlet located in the island’s northwest and historical water quality data. At each station, three transects measuring 50 by 5 meters were surveyed, counting only conspicuous species. All censuses were performed by the same observer to minimize variability.
Impacted sites exhibited relatively high fish abundance but reduced species richness and functional richness. Trait-based analyses revealed that a specific set of traits were disproportionately excluded from impacted sites, while others persisted. Our findings underscore that it is not individual traits but rather specific combinations of traits that mediate species presence or exclusion in polluted reef habitats.