Occurrence, biotic interactions, and ecotoxicological impacts of microplastics in the East African coastal environment: Insights and research priorities from the MICROMARINE Project

Microplastic pollution is an emerging concern in East African coastal systems, yet the region remains underrepresented in global assessments. This paper synthesises findings from the MICROMARINE project and other regional studies to evaluate (i) environmental occurrence, (ii) biotic interactions, and (iii) ecotoxicological impacts of microplastics along the Kenyan and Tanzanian coasts into a narrative review. Microplastics are consistently detected in surface waters, sediments, and biota, with spatial variability often driven by urbanisation, riverine inputs, and local hydrodynamics. Fibers and fragments dominate across environmental compartments, although a substantial proportion of fibers may be natural or semi-synthetic, highlighting the importance of polymer identification. Despite widespread occurrence, current evidence suggests that organismal burdens in fish and bivalves do not consistently correlate with environmental concentrations, although this relationship remains uncertain given limited paired studies and species coverage, indicating that ingestion is influenced by feeding behaviour and exposure pathways rather than ambient levels alone. Regional experimental studies (derived largely from a freshwater teleost model) demonstrate that ingestion can cause intestinal damage, reduced growth, and altered energy allocation, providing a mechanistic basis for individual effects, but population-level impacts remain understudied. Building on these empirical studies, we identify research priorities across short-, medium-, and longer-term timescales, emphasising the need for existing knowledge to inform mitigation strategies, align regional research with global advances, and integrate plastic pollution within broader environmental concerns, namely climate change and biodiversity loss. Collectively, these findings provide an integrated regional synthesis and position East Africa as an increasingly important contributor to global microplastics research.