Environmental contamination is a problem that reduces the quality of ecosystems and may make them unsuitable to accommodate life. As many ecosystems are connected, some organisms avoid the stress from continuous exposure to contaminants by moving towards less disturbed areas. However, the landscapes in which organisms move might vary regarding the concentrations of contaminants, in the form of gradients or patches of contamination. Therefore, although it is expected that organisms prefer clean areas, their sporadic contact with contamination should not be ignored, as the greater the probability of being in contact with contaminated areas, the higher the stress. The aim of this study was to assess how the stress (cortisol levels) of zebrafish (Danio rerio) varies as a consequence of heterogeneity in the chemical composition of the habitats and the presence of uncontaminated areas in this heterogeneous landscape. Zebrafish were exposed to heterogeneous contamination scenarios containing different concentrations of copper along a free-choice multi-compartmented system, in which they were able to flee from the most contaminated areas. Fish escaped from the most contaminated areas with an avoidance by 50% of population (AC50) at concentrations of 41 (copper gradient scenario), 25 (spatially limited contamination scenario) and 69 (highly contaminated scenario) μg/L. Higher cortisol levels were observed in the populations exposed to homogeneously contaminated and highly contaminated (by copper) scenarios (both with no acceptable clean area to flee to). In summary, the uncontaminated areas might be crucial for the spatial dynamics of fish populations in a chemically heterogeneous landscape due to their role as escape zones to alleviate stress.
Keywords: Avoidance; Copper; Cortisol; Habitat heterogeneity; Stress ecology.
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