Microplastic ingestion by two estuarine-associated mullet species, Chelon richardsonii and Chelon dumerili in the Breede Estuary, South Africa

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Microplastic (MP) ingestion in fish has the potential to cause a multitude of damaging effects to both organisms and the environment. Microplastics (MPs) are defined as solid plastic particles ≤ 5mm in size. The small size of MPs makes them extremely hazardous, as they imitate a range of food items on which organisms feed. Rivers and estuaries are links between terrestrial and marine ecosystems; thus, these systems hold key evidence of the magnitude and nature of MP pollution. Research particularly in the southern hemisphere is poorly documented for MP ingestion. This study shows MP ingestion by two mullet species (Chelon richardsonii &amp; Chelon dumerili) in the Breede Estuary, South Africa. It was found that 98.4 % of the captured fish had ingested MPs and ingestion took place throughout the estuary reaches by both species. Multiple brown/orange fragments and the concentration of MPs found in the large mullet (≥200mm), were consistent with results found in sediment samples, indicating large (≥200mm) mullet intake MPs via sediment ingestion. The previous trend was not identified in small mullet (<200mm), thus indicating small mullet selectively fed on particles and MPs in the water column. Small juvenile fish (<200mm) ingested concentrations of MPs one order of magnitude greater than large (≥200mm) adult fish throughout the estuary, possibly reflecting the feeding transition from planktivorous juveniles to benthic adult detritivores. The MP conc. (MP.g-1) in small mullet (<200mm) was significantly (p<1.639e-12) higher compared to large mullet (≥200mm). A significant difference (p<0.008) was found between MP conc. (MP.g−1) and species, this interspecific differentiation was driven by small (<200 mm) fish, which selectively and visually feed. This study provides insights and new knowledge regarding MP pathways within food webs. It is imperative that a better understanding of MP pathways through marine food webs is established on a local, regional, and global scale in order to mitigate the resulting risks associated with fish, humans, and any other animal-related consumption. Keywords: Breede River . Estuary . Microplastic concentrations . Mugilidae . Sediment pollution . South Africa