Plastic Pollution as a Driver of Aquatic Biodiversity Decline: Mechanisms, Ecological Consequences, and Mitigation Imperatives

Plastic pollution has emerged as one of the most pervasive and ecologically disruptive anthropogenic stressors confronting aquatic ecosystems in the twenty-first century. The present review synthesizes evidence from peer-reviewed literature on the sources, transport pathways, and biological impacts of macro- and microplastic contamination across marine, freshwater, and coastal environments. Physical interactions including ingestion and entanglement inflict direct physiological harm on taxonomically diverse organisms such as fish, sea turtles, seabirds, and marine mammals, manifesting as internal injuries, impaired feeding, compromised reproduction, and mortality. Microplastics (< 5 mm) present additional sublethal hazards by functioning as vectors for persistent organic pollutants and heavy metals, facilitating bioaccumulation and trophic transfer through food webs. Soil-dwelling fauna, including earthworms and nematodes, are similarly affected, with cascading consequences for nutrient cycling and edaphic biodiversity. At the ecosystem level, plastic pollution reduces species richness, degrades critical habitats such as coral reefs and mangroves, and undermines the provisioning of essential ecosystem services. The contamination of aquatic food chains further raises concern for human health via dietary exposure. Effective mitigation requires concerted international policy action, enhancement of waste management infrastructure, reduction of single-use plastic consumption, and sustained investment in biodegradable material alternatives.