Growing anthropogenic impacts on ecosystems pose a serious threat to biodiversity and environmental health, with effects that extend along food webs right up to humans. In this context, the identification of sentinel organisms and early-warning molecular biomarkers is a priority, especially from a One Health perspective, which recognizes the intrinsic connection between the health of ecosystems, animals, and humans.

In this regard, variation in mitochondrial genome copy number (mtDNAcn) represents a promising candidate because of its vulnerability to oxidative stress. Although mtDNAcn is already recognised in clinical practice as a marker of oxidant-mediated diseases, its use in wild organisms remains unexplored, representing a frontier of scientific and translational interest.

The contribution reported here aims to address this gap through three investigations conducted at a Site of National Interest (SNI) in eastern Sicily, characterized by historical and widespread contamination, which represented one of the most concerning sources of Hg at Mediterranean scale.

In the first study, the leafhopper Opsius heydeni — a sap-feeder on Tamarix spp., plants known for accumulating heavy metals — shows a mtDNAcn reduction in the SNI compared to the control site. The second research, conducted on three commercial fish species, confirms a relationship between mercury bioaccumulation levels and mtDNAcn variations. Furthermore, the findings appear species-specific — a decrease in Mullus barbatus and Pagellus erythrinus, and an increase in Diplodus annularis were observed — reflecting ecological and physiological differences. The third study introduces the blue crab Callinectes sapidus, an alien and edible species, as a potential bioindicator in Mediterranean Sea, detecting a mtDNAcn reduction in SNI specimens.

Overall, these outcomes support mtDNAcn as a promising early-warning tool capable of reflecting oxidative stress triggered by contaminants in phylogenetically distant taxa. Further comparative researches across animal species are recommended to strengthen its use in integrated environmental monitoring, in line with a One Health approach.