The Republic of Mauritius is a big ocean state which has a large exclusive economic zone of 2.1 million Km² and its population is dependent on its marine environment and resources for local livelihood, tourism, economic growth and well-being. Such small island developing states are vulnerable to local and global stressors, including plastics polltion. The dynamics of microplastics (MPs) in the two islands, namely mainland Mauritius and Rodrigues island, are not understudied and not well understood. This study aimed to characterize the spatial and seasonal trends in the abundance and composition of microplastics (MPs) in beach sediment at windward and leeward sites around both islands, during summer (December 2023 to January 2024) and winter (June to July 2024) seasons. The Western Indian Ocean Marine Science Asscociation (WIOMSA) and Sustainable Seas Trust (SST) African Marine Litter Monitoring protocol (2023) was adated in this study. Belt transects were placed in triplicates (n=3 per site) perpendicular to the beach and from the vegetation line  to the low water mark (LWM). Surface sediment (top 2.5 cm layer) was sampled from quadrats (0.5x0.5 m) placed at three different zones (vegetation line, beach slope and low water mark) along the transect. Results indicated a dominance of MPs in winter season for both islands. In Rodrigues, MPs density was least at St Francois beach (north-east coast) at 27.7±135.9 particles mˉ² and highest at Mourouk beach (south-east coast) at 43.7±10.9 particles mˉ². For Mauritius, highest MPs density was recorded at Belle Mare beach (east coast) at 72.7±16.9 particles mˉ² and lowest density (12.33±2.91 particles mˉ²) at Bel Ombre (south coast). Highest MPs density was recorded at the vegetation line (VL) in both islands, to the exception of Riambel (south coast) and Tamarin (west coast) beach sites in Mauritius, where highest MPs density was at the low water mark zone suggesting a recent oceanic input. Fragments (79.6%) were the most abundant MP shape followed by fibres (17.8%). Blue (49.6%) was the most abundant colour followed by white (29.7%). A PERMANOVA test indicated that there is a significant difference between the two Islands where Mauritius is in fact a subset of Rodrigues Island, and that Rodrigues is the scene of much more spatially heterogeneous pollution than Mauritius despite its lower population size. The results indicated an oceanic input for microplastics on the beaches of Rodrigues island that could be driven by wind and sea currents. The findings provide a baseline for focused clean-ups and strategic directions and policy measures for plastic pollution control and prevention.

 

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