Abstract
Marine plastic abundance has increased over the past 60 years and microplastics (< 5 mm) constitute a primary component of such litter. Filter-feeding megafauna, such as the whale shark, might be particularly affected by microplastic pollution as their feeding mode requires filtration of up to thousands of cubic meters of water. In addition, the habitat range of whale sharks intersects with several recognized microplastic pollution hotspots, among which is the Coral Triangle. Direct evidence for microplastic ingestion in whale sharks however, has not yet been presented. Here we show that whale shark scat collected in the Philippines from 2012 to 2019 contained a mean of 2.8 microplastics g− 1. Contrary to our expectations, the microplastic concentration in the scat remained consistent from 2012 to 2019. Water samples from the study site in 2019 indicated that the local microplastic pollution (5.83 particles m− 3) was higher than in surface waters in other whale shark habitats, but well below other pollution hot-spots found in Southeast Asia and China (range: 100–4100 particles m− 3). With the predicted growth in plastic use, leading to increased plastic marine pollution, whale sharks are expected to become more exposed to this form of pollution. To what extent microplastic ingestion impacts the overall health status of this endangered species remains an open question.
Highlights
Marine plastic pollution is a global problem acknowledged under the United Nations Sustainable Growth Development Goal 14 - life below water
We isolated 393 potential microplastic particles (MP, particle size > 300 μm due to technical constraints); Attenuated total reflection Fourier-transform infrared spectroscopy (FTIR) analysis supported 46.5% (n = 179) of these to be of synthetic origin, and confirmed that 47 of the 99 samples contained at least 1 MP
We present a thorough assessment of whale shark scat for the first direct evidence of microplastic (MP) ingestion in this species
Summary
Marine plastic pollution is a global problem acknowledged under the United Nations Sustainable Growth Development Goal 14 - life below water. Plastics break down into increasingly smaller particles [2], such as microplastics, which are most commonly considered as particles < 5 mm [3]. Even though the average mesh diameter of the filter pads may theoretically be permissive to smaller microplastics Isotopic analyses have (2021) 1:17 revealed that whale shark diets can consist of a diverse range of prey, such as shrimp and copepods, as well as myctophid fishes [11]–prey which has been reported to ingest microplastic in the natural environment [12,13,14]. Opportunistic sampling of stranded whale sharks has confirmed that larger plastic items are ingested [16,17,18,19], but to date, evidence of direct microplastic ingestion is lacking
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