Distribution and Uptake of Microplastics in Key Species of the Bulgarian Black Sea Ecosystem and Their Effects from a Stress Ecology Viewpoint

Plastic pollution in marine environments poses a new global threat. Microplastics (MPs) can bioaccumulate in marine organisms, leading to oxidative stress (OS). This study investigates MPs accumulation and associated OS responses in six invertebrate species (Bivalvia, Gastropoda, Malacostraca) and three key fish species of the Bulgarian Black Sea ecosystems. Hydrobionts were collected from representative coastal habitats, MPs were quantified microscopically, and OS biomarkers (lipid peroxidation, glutathione, antioxidant enzymes) were analyzed spectrometrically in fish liver and gills, and invertebrate soft tissues. Results revealed species-specific MPs bioaccumulation, with Palaemon adspersus, Rathke (1837) and Sprattus sprattus (Linnaeus, 1758) having the highest concentrations per gram soft tissue and muscle, respectively. The alien Pacific oyster exhibited higher MPs loads than the native species. OS biomarkers varied markedly among species, reflecting different stress responses. Cluster analyses indicated that MPs were mainly grouped with catalase activity in all species. The specific OS (SOS) index showed that OS levels were linked to both habitat conditions and species-specific antioxidant defense. These findings confirmed the importance of environmental conditions, including MPs pollution, and evolutionarily developed adaptation capacity of organisms for tolerance and resilience to induced stress. The study emphasizes the need for monitoring MPs and OS to better assess the ecological risk.