Accumulation of microplastics in various organs of fiddler crabs and sea cucumbers across the coastal habitats in Singapore
Jenny Fong, Ashwini Suresh Kumar, Zhen Yu Choy, Yi Tan, Jasmine Anya Putri Gowidjaja, Mei Lin Neo
Abstract
Microplastics (or MPs) are an emergent threat to marine organisms. This study assessed MP contamination in the major organs of four species from Singapore's coastal habitats: Orange Fiddler Crab ( Gelasimus vocans ) and Porcelain Fiddler Crab ( Austruca annulipes ) from mangroves, Garlic Bread Sea Cucumber ( Holothuria scabra ) from seagrass beds and Synaptid Sea Cucumber ( Synaptula recta ) from coral reefs. MPs were prevalent in all species and their organs. Mean MP concentrations in fiddler crabs were 6.63 ± 0.97 MP individual −1 in G . vocans and 12.18 ± 3.38 MP individual −1 in A . annulipes , where their female crabs had significantly more MPs than males. This study also confirmed the translocation of MPs to the crabs' hepatopancreas, which had the highest MP concentrations compared to gills and digestive tracts. These observations suggest that the fiddler crabs' sexual dimorphism could influence feeding efficiency and behaviour. In contrast, the sea cucumbers had lower MP concentrations in their organs, where the average MP concentrations were 10.00 ± 2.32 MP individual −1 in H . scabra and 6.33 ± 0.69 MP individual −1 in S . recta . For H. scabra only, their respiratory trees showed the highest MP levels compared to their digestive tracts. Across the species, MPs were predominantly <1,000 μm in size, in fibre shape and polyethylene (PE). These findings provide critical baseline data on MP contamination across different organs in marine organisms, serving as proxies for MP pollution levels in the environment. • Microplastics were ubiquitous in all organs of the fiddler crabs and sea cucumbers. • Sea cucumbers reported lower microplastic concentrations across their organs compared to the fiddler crabs. • Microplastic shapes detected were fibre > fragment > film > sphere. • Microplastic polymers detected were PE > PP > PE + PP > PS > PET > PVC > PCU. • Findings here may serve as proxies to infer the levels of microplastic pollution in the environment.