Iron pollution has minor impacts on the behavioral ecology of the Brazilian endemic reef damselfish Stegastes fuscus.

Coral reefs face profound threats from global and local stressors, including coastal pollution from human activities like mining. This study investigates the potential impacts of increased iron (Fe) on the behavioral ecology of juvenile Stegastes fuscus, a pivotal territorial damselfish species on Brazilian reefs affected by a major mining dam disaster. In a controlled mesocosm experiment over 28 days, 16 damselfish (16 experimental tanks, one fish per tank, four fish per treatment) were exposed to a gradient of iron concentrations, from background in coastal seawater to maximum values recorded in the ocean after the dam collapse (over 900 μg L). We monitored habitat use, feeding activity, and intraspecific aggression through video analyses, and quantified iron bioaccumulation in fish tissues. Iron enrichment did not significantly alter habitat use, with branching fire-coral (Millepora alcicornis) consistently preferred across treatments, or aggression levels. However, feeding patterns showed changes, particularly an increase in bites over Sargassum sp. blades at the highest Fe concentration (900 μg L). The limited ecological impacts observed may be explained by the low Fe bioaccumulation in fish tissues, suggesting physiological mechanisms of bioaccumulation avoidance, or insufficient exposure duration. Our findings highlight the importance of longer-term experiments and broader ecological contexts when assessing pollution impacts on coral reef fish.