Weathered oil fragments as an ecotoxic legacy of ocean oil spills: Developmental and redox disruption in necrophagous Chrysomya albiceps larvae

Oil spills in marine and coastal environments represent one of the most severe ecotoxicological threats, with effects that can persist for years due to the formation of weathered oil fragments (WOFs). These residues accumulate on beaches and shorelines, acting as continuous sources of exposure and constituting a long-term legacy of spills that remains largely unexplored, particularly in the context of decomposition and necrophagous interactions. In this study, we simulated mammalian mortality in contact with WOFs and assessed their effects on the development of the necrophagous fly Chrysomya albiceps , a species of recognized ecological relevance. For this purpose, Swiss mouse carcasses were contaminated through direct contact with WOFs and subsequently offered as a feeding substrate to larvae over a 96 h experimental period. Our results revealed a drastic reduction in larval productivity and a complete developmental arrest before reaching the third instar in contaminated carcasses, which was accompanied by significantly lower values of developmental and biomass indices, including the Weighted Mean Stage Index (WMSI), Weighted Biomass Stage Index (WBSI), Larval Biomass Efficiency (LBE), and Cumulative Larval Development Index (CLDI). At the biochemical level, we observed an exacerbated pro-oxidant state, characterized by increased production of reactive oxygen species (ROS) and malondialdehyde (MDA), along with reduced activity of antioxidant enzymes, including superoxide dismutase (SOD) and catalase (CAT), resulting in a clear redox imbalance. Multivariate analyses, including Permutational Multivariate Analysis of Variance (PERMANOVA) and Partial Least Squares Discriminant Analysis (PLS-DA), confirmed group segregation. In contrast, network analysis revealed a systemic reconfiguration of biochemical interactions, with oxidative damage biomarkers assuming central roles. Structural equation modeling (SEM) further indicated a negative association between larval performance and oxidative stress, suggesting that improved ontogenetic progression was linked to reduced redox pressure. Taken together, our study provides the first evidence that persistent residues derived from marine oil spills can impair key processes in decomposition ecology, representing a previously unrecognized impact whose insidious nature may pose long-lasting risks to nutrient cycling and the resilience of coastal ecosystems. • Weathered oil fragments reduced larval productivity by ≈70%. • No larvae reached the 3rd instar under WOF-contaminated carcasses. • WOF exposure triggered severe oxidative stress and enzyme inhibition. • Biochemical networks were reorganized toward oxidative damage markers. • WOFs threaten necrophagous dynamics, decomposition, and nutrient cycling.