Microplastics and sea turtle reproduction: A systematic review on nest contamination and developmental risks

Microplastic (MP) contamination is a notable environmental challenge affecting marine ecosystems. However, its repercussions on the reproductive success of sea turtles remain inadequately elucidated. In this systematic review, we aggregated global data on the prevalence, characteristics, and biological ramifications of MPs within sea turtle nesting habitats and developmental stages. Information was compiled from studies conducted across principal nesting sites, including China, Malaysia, Mexico, Japan, and the Mediterranean region, based on the PRISMA guidelines. The findings revealed substantial spatial heterogeneity in MP concentrations, from 1513 particles/m² on the Qilianyu Islands to ˃12,000 items/kg of dry sand on Redang Island. Polyethylene (PE), polystyrene (PS), and polyethylene terephthalate (PET) were the predominant types of MPs, which primarily manifested in fiber and foam forms. Evidence indicates that MPs permeate the nesting substrate, including sediment layers corresponding to egg incubation depth, and accumulate within turtle eggs, yolks, and embryonic tissues. Phthalate esters (PAEs) and MP particles measuring ˂5 µm were identified in yolk and liver tissues, indicating maternal transfer and the potential for endocrine disruption. Sublethal effects included increased melanomacrophage activity in embryos, intestinal obstruction, and reduced body condition in post-hatchlings. Additionally, dark-hued MPs may increase nesting temperatures, thereby affecting sex ratios in temperature-dependent sex determination (TSD) frameworks. These findings suggest that persistent MP exposure may impair embryonic development, alter hatchling fitness, and potentially reduce long-term population recruitment and resilience. Mitigating microplastic pollution is essential for ensuring the reproductive viability, population resilience, and enduring conservation of sea turtle species.