Use of pelagic tunicate Salpa fusiformis as biological sampler to estimate in-situ density of microplastics smaller than 330 µm.

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.

Floating plastic accumulation and distribution around Kuroshio Current, western North Pacific.

The distribution of floating plastic debris around the Kuroshio Current which transports plastics from the coastal waters of Asian countries to North Pacific subtropical gyre, was investigated in 2014. The mean abundance and weight of plastic debris on the sea surface were 100,376 counts/km2 and 446.16 g/km2, respectively. Intensive plastic accumulation was observed in the frontal area between the northern edge of the Kuroshio and coastal waters off Shikoku, while a relatively higher abundance in the south of Kuroshio was generally associated with anticyclonic mesoscale eddies. Such an accumulation resulted from the eddy-Kuroshio interactions which are specifically associated with the offshore non-large meandering Kuroshio path. Overall, white, fragmented, small-sized (≤1 mm) particles with polyethylene and polypropylene polymers were dominant. In the southern area of Kuroshio, the contribution of polystyrene and larger-sized plastic was higher, suggesting a rapid influx of fresh particles from western Japan to offshore by the northwest monsoon.

Large-scale distribution and composition of floating plastic debris in the transition region of the North Pacific.

Floating plastic debris was investigated in the transition region in the North Pacific between 141°E and 165°W to understand its transportation process from Asian coast to central subtropical Pacific. Distribution was influenced primarily by the current system and the generation process of the high concentration area differed between the western and eastern areas. West of 180°, debris largely accumulated around nearshore convergent area and was transported by eddies and quasi-stationary jet from south to the subarctic region. The average was 15% higher than that previously reported in 1989, suggesting an increase in plastic debris in 30 years. East of 180°, debris concentrated in the calm water downstream of the Kuroshio Extension Bifurcation with considerably high concentration (505,032 ± 991,989 pieces km-2), due to the accumulation of small transparent film caused by calm weather conditions, suggesting a further investigation on small plastic (<1 mm) in the subsurface depth in the subtropical North Pacific.