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Use of pelagic tunicate Salpa fusiformis as biological sampler to estimate in-situ density of microplastics smaller than 330 μm
Summary
Researchers found that the gut contents of salps — ocean filter feeders — closely mirror the microplastic composition of surrounding seawater, making them a useful biological sampler for estimating concentrations of very small microplastics (under 330 micrometers) that standard nets cannot capture. This method could help fill a major gap in ocean microplastic monitoring and improve estimates of how much small plastic is circulating in marine food webs.
While microplastics (MPs) have emerged as a significant threat, information on MPs <330 μm (SMPs) is limited by the lack of simple quantification methods. We examined the potential application of salps, non-selective filter-feeding tunicates, to estimate in-situ SMP densities. After collection, salp guts were dissected, dissolved, and filtered to analyze MPs using μFTIR. The results showed each gut samples contained 1.96 ± 1.49 MP particles; their polymer composition and size were consistent with those in ambient seawater. When the SMP quantity in salp gut was converted to in-situ densities using previously published feeding parameters, SMP densities ranged between 235 and 1209 particles/m3; they were strongly correlated with those in seawater. Importantly, this method, which is less labor intensive than other methods, could easily characterize in-situ SMP distribution of different marine environments, thus improve the monitoring of their pollution. Furthermore, it could be applied to examine historical contributions of SMPs using archived salp samples.
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