Environmental insights from non-target detections in urban eDNA metabarcoding

Metabarcoding amplifies environmental DNA (eDNA) but often yields non-target taxa and false positives. Urban ecosystems are particularly prone to such detections due to inflows of external genetic material, yet their interpretation in urban eDNA studies remains unclear. This study examined non-target occurrences from fish-targeted metabarcoding in inland urban freshwater systems and proposes a perspective on interpreting such detections as ecologically meaningful signals rather than analytical noise. From 32 samples, 27.8% of total reads were non-targets, including 30 species from 21 families of non-target taxa and 35 species from 20 families of marine fish. Non-target taxa were most common in rivers, whereas marine fish appeared near wastewater facilities, reflecting human-derived inputs. These findings highlight that unexpected eDNA detections may reveal overlooked ecological and anthropogenic signals, offering insights for more reliable biodiversity assessment and management in urban ecosystems.