Microplastic pollution has reached every ocean ecosystem, with profound welfare implications for marine wildlife. Seabirds, sea turtles, marine mammals, and fish ingest plastic debris either directly or through contaminated prey. Albatrosses feed plastic to chicks, causing starvation through gut blockage and providing a false sense of satiety. Sea turtles mistake plastic bags for jellyfish; ingestion causes intestinal obstruction, buoyancy problems, and death. Entanglement in macroplastics (nets, packaging straps) causes traumatic injury, drowning, and chronic welfare compromise. Microplastic particles (<5mm) accumulate in fish guts, potentially causing inflammation and oxidative stress. Chemical contamination of plastics (phthalates, BPA, PCBs) leaches into tissues, causing endocrine disruption. Research estimates 90% of seabirds have ingested plastic. Welfare mitigation requires systemic plastic reduction alongside rescue and rehabilitation of affected wildlife. UNEP Global Plastics Treaty negotiations aim to address plastic production and waste at source.