peer reviewed | Neustonic microplastic and zooplankton abundance was determined in the North Western Mediterranean Sea during a summer cruise between July 9th and August 6th 2010, with a break between July 22th and 25th due to a strong wind event. Ninety percent of the 40 stations contained microplastic particles (size 0.3-5 mm) of various compositions: e.g., filaments, polystyrene, thin plastic films. An average concentration of 0.116 particles/m² was observed. The highest abundances (> 0.36 particles/m²) were observed in the shelf stations. The neustonic plastic particles concentrations were 5 times higher before than after the strong wind event which increased the mixing and the vertical repartition of plastic particles in the upper layers of the water column. The values rise in the same order of magnitude than in the North Pacific Gyre. The average ratio between microplastics and mesozooplankton weights was 0.5 for the whole survey and might induce a potential confusion for zooplankton feeders.

peer reviewed | The annual variation in neustonic plastic particles and zooplankton was studied in the Bay of Calvi 23 (Corsica) between 30 August 2011 and 7 August 2012. Plastic particles were classified into three size classes, small microplastics (0.2–2 mm), large microplastics (2–5 mm) and mesoplastics (5–10 mm). 74% of the 38 samples contained plastic particles of varying composition: e.g. filaments, polystyrene, thin plastic films. An average concentration of 6.2 particles/100 m2 was observed. The highest abundance values (69 particles/100 m2) observed occurred during periods of low offshore wind conditions. These values rose in the same order of magnitude as in previous studies in the North Western Mediterranean. The relationships between the abundance values of the size classes between zooplankton and plastic particles were then examined. The ratio for the intermediate size class (2–5 mm) reached 2.73. This would suggest a potential confusion for predators regarding planktonic prey of this size class.

Levels of marine debris, including microplastics, are largely un-documented in the Northeast Atlantic Ocean. Broad scale monitoring efforts are required to understand the distribution, abundance and ecological implications of microplastic pollution. A method of continuous sampling was developed to be conducted in conjunction with a wide range of vessel operations to maximise vessel time. Transects covering a total of 12,700km were sampled through continuous monitoring of open ocean sub-surface water resulting in 470 samples. Items classified as potential plastics were identified in 94% of samples. A total of 2315particles were identified, 89% were less than 5mm in length classifying them as microplastics. Average plastic abundance in the Northeast Atlantic was calculated as 2.46particlesm−3. This is the first report to demonstrate the ubiquitous nature of microplastic pollution in the Northeast Atlantic Ocean and to present a potential method for standardised monitoring of microplastic pollution.

Numerical models point to the south-east Bay of Biscay as a convergence area for floating particles, including plastics. The few existing studies on plastic abundance in the area mainly focus on open waters and yet information on the coastal area is limited. To fill this gap, neustonic samples were taken along the coastal waters of the south-east Bay of Biscay (2017–2020) to define the spatial distribution of plastic abundances and composition. Results show an average plastic abundance of 739,395 ± 2,625,271 items/km² (998 ± 4338 g/km²). French waters were more affected, with five times higher plastic abundances than Spanish coasts. Microplastics represented 93 % of the total abundance of plastic items (28 % in weight), mesoplastics 7 % (26 %) and macroplastics 1 % (46 %). This study demonstrates that this area is a hotspot for plastic with levels in coastal waters similar to those in the Mediterranean Sea or other litter aggregation areas.

Microplastic ingestion by mesozooplankton may be an important pathway for the microplastics to enter the food web. To determine microplastic abundance in Guanabara Bay, samples were collected by neustonic haul with a 64-μm-net and oblique hauls using 64- and 200-μm nets. Microplastic size and abundance as well as copepod, fish-larvae, and chaetognath sizes, densities, and preferential prey sizes were determined. Microplastic abundance was higher in samples collected with fine nets (average 4.8 microplastics m−3, maximum 11 microplastics m−3) than in those collected with coarse net. Microplastic abundance in Guanabara Bay was higher than that in other marine ecosystems. Microplastics >100 μm were too large to be ingested by copepods. However, for fish larvae and chaetognaths, the abundance of microplastics, at the corresponding prey size range, were, respectively, ~9000- and 14,400-folds lower than the preferential copepod prey, in the same size range. Thus, in Guanabara Bay, microplastics were available, but too diluted to be frequently ingested by fish larvae and chaetognaths.

Research on marine microplastics continues to increase in popularity, with a large number of studies being published every year. However, with this plethora of research comes the need for a standardised approach to quantification and analysis procedures in order to produce comparative assessments. Using data collected from neuston nets in 2016, parameters for quantifying microplastics were compared. Surface area was the most accurate parameter to describe plastic size and should be used to describe plastic quantity (per km2 or m3), alongside abundance. Of the two most commonly used methods for calculating plastic concentration (flowmeter and ship's log), ship's log provided consistently smaller abundances, with the exception of one sample, calling for a standardisation in the techniques and measurements used to quantify floating microplastics.

The annual variation in neustonic plastic particles and zooplankton was studied in the Bay of Calvi (Corsica) between 30 August 2011 and 7 August 2012. Plastic particles were classified into three size classes, small microplastics (0.2–2 mm), large microplastics (2–5 mm) and mesoplastics (5–10 mm). 74% of the 38 samples contained plastic particles of varying composition: e.g. filaments, polystyrene, thin plastic films. An average concentration of 6.2 particles/100 m2 was observed. The highest abundance values (69 particles/100 m2) observed occurred during periods of low offshore wind conditions. These values rose in the same order of magnitude as in previous studies in the North Western Mediterranean. The relationships between the abundance values of the size classes between zooplankton and plastic particles were then examined. The ratio for the intermediate size class (2–5 mm) reached 2.73. This would suggest a potential confusion for predators regarding planktonic prey of this size class.