Aplicación del modelo Size-Spectrum para evaluar la integridad ecológica de la comunidad íctica en tres cuerpos de agua de Villeta, Colombia.

Abstract

The degradation of aquatic ecosystems is one of the most pressing environmental challenges on a global scale. Rivers and streams harbor a disproportionate share of the planet’s biodiversity and, at the same time, are among the ecosystems most threatened by pollution, alterations to the hydrological regime, habitat loss, and the introduction of non-native species (Dudgeon et al., 2006; Reid et al., 2019). In light of this situation, the assessment of ecological integrity, defined as an ecosystem’s capacity to sustain a community of organisms comparable, in composition, diversity, and functional organization, to that of the region’s natural habitats (Karr, 1981), has established itself as a tool for environmental diagnosis and management decision-making (Roldán Pérez & Ramírez Restrepo, 2008). Colombia is a country characterized by a great diversity of aquatic ecosystems; the assessment of ecological integrity in these environments has relied primarily on the use of biotic indices based on macroinvertebrates, such as the BMWP/Col (Álvarez, 2005; Roldán, 2003), as well as fish community indices adapted from Karr’s (1981) Index of Biotic Integrity (IBI). These indices, recommended by national regulations for the monitoring of inland waters (Ministry of Environment and Sustainable Development, 2021), require the taxonomic identification of organisms at the family or species level, which demands specialized knowledge of hydrobiological communities and hinders their widespread application throughout the country, particularly in regions with high fish diversity and limited taxonomic inventory. It should be noted that, although there are some adaptations of the IBI for fish communities in the country, none of the indices officially authorized for environmental licensing in Colombia are based exclusively on ichthyofauna (all use macroinvertebrates or other groups), which leaves a methodological gap that supports the exploration of ichthyological and ataxonomic approaches, such as the Size-Spectrum methodology. The Size-Spectrum model, initially proposed by Sheldon et al. (1972) and formalized by Kerr (1974), is a methodological alternative that has gained international prominence. This approach describes the linear relationship (on a logarithmic scale) between the abundance of organisms in an aquatic community and their body size, reflecting emergent properties such as ecosystem carrying capacity, predator-prey interactions, and energy flows between trophic levels (Edwards et al., 2017; Sprules & Barth, 2016). By dispensing with taxonomic identification and relying solely on morphometric measurements, the Size-Spectrum approach is a particularly useful tool in contexts where taxonomic information is scarce. In Colombia, the application of the Size-Spectrum approach to fish communities has been limited to the marine environment. Gómez-Canchong et al. (2011) characterized the size structure of demersal fish assemblages in the Colombian Caribbean and documented changes associated with fishing pressure. More recently, Páramo & Pérez (2024) used size-based indicators to assess the status of populations in the same region. However, to date, no studies have been reported that apply the Size-Spectrum model to fish communities in Colombian inland waters, which constitutes a significant knowledge gap given the extent and diversity of the country’s water network and the growing anthropogenic pressure on these water bodies. For this reason, the objective of this study was to assess the ecological integrity of fish communities in the Santibáñez Creek, the Namay River, and the Cune Creek, in order to analyze the sensitivity of the Size-Spectrum model as a tool to support management decision-making. Fish communities are considered effective bioindicators of ecological integrity in aquatic ecosystems. A bioindicator species is one whose presence, abundance, or physiological condition consistently and measurably reflects the environmental state of the habitat in which it is found (Markert et al., 2003; Siddig et al., 2016). Although not all fish meet this criterion (such as species at basal trophic levels or those with broad environmental tolerance, which tend to respond less specifically to disturbances), various fish groups, particularly top predators and species with greater longevity, accumulate the cumulative effects of pollutants and habitat alterations throughout the food web, making them sensitive indicators of ecosystem quality (Jennings, 2005; Whitfield & Elliott, 2002). The trophic structure and size classes of a fish community can be affected by anthropogenic or environmental pressures; identifying these changes provides insight into the ecological status of an ecosystem and, based on this, helps guide conservation strategies and management plans to restore ecological integrity, while ensuring the sustainable use of fish and water resources.