Microplastics in the Indian Ocean: a review of the ingestion and trophic transfer in commercial pelagic fish

Microplastics (MPs) are ubiquitous in our environment. Their appearance in natural habitats causes them to be mistaken for food by marine organisms, and ingested MPs are ultimately transferred along the food chain. This review aimed to analyse the current knowledge on MPs ingestion and trophic transfer in commercial pelagic species of the Indian Ocean (IO) which has the second-largest plastic load in the world. A total of 37 evidently reliable studies were included. The main results showed that the percentage of incidence in 70 species of commercially important pelagic and semi-pelagic fish in the Indian Ocean is 60%. The maximum average abundance of MPs reported was 57.1 ± 3.3 items/individual in the Hilsa shad (Hilsa Ilisha). Blue particles and fibres were the prevalent colour and shape (in 52% and 73% of the studies respectively) while particles measuring less than 500 µm were predominant in the majority of the studies (54%). Polyethylene was reported as being the most abundant polymer in 56% of studies which have reported polymer abundance. Gaps were identified in the geographical coverage of the IO for the study of MPs ingestion by commercial pelagic species, and studies investigating the relationship between trophic level and MPs ingestion are very scarce in the region. The findings of the individual studies on trophic transfer were contradictory, while the Trophic Magnification Factor (TMF) calculated in this review indicated that lower trophic levels ingested more MPs. Factors influencing trophic interactions should therefore be given careful attention and focus in future research to better understand the risk for human health.