Annual variation in neustonic micro- and meso-plastic particles and zooplankton in the Bay of Calvi (Mediterranean–Corsica)

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.     

The size, mass, and composition of plastic debris in the western North Atlantic Ocean

This study reports the first inventory of physical properties of individual plastic debris in the North Atlantic. We analyzed 748 samples for size, mass, and material composition collected from surface net tows on 11 expeditions from Cape Cod, Massachusetts to the Caribbean Sea between 1991 and 2007. Particles were mostly fragments less than 10 mm in size with nearly all lighter than 0.05 g. Material densities ranged from 0.808 to 1.24 g ml⁻¹, with about half between 0.97 and 1.04 g ml⁻¹, a range not typically found in virgin plastics. Elemental analysis suggests that samples in this density range are consistent with polypropylene and polyethylene whose densities have increased, likely due to biofouling. Pelagic densities varied considerably from that of beach plastic debris, suggesting that plastic particles are modified during their residence at sea. These analyses provide clues in understanding particle fate and potential debris sources, and address ecological implications of pelagic plastic debris.     

A comparison of neustonic plastic and zooplankton abundance in southern California's coastal waters

The density of neustonic plastic particles was compared to that of zooplankton in the coastal ocean near Long Beach, California. Two trawl surveys were conducted, one after an extended dry period when there was little land-based runoff, the second shortly after a storm when runoff was extensive. On each survey, neuston samples were collected at five sites along a transect parallel to shore using a manta trawl lined with 333 micro mesh. Average plastic density during the study was 8 pieces per cubic meter, though density after the storm was seven times that prior to the storm. The mass of plastics was also higher after the storm, though the storm effect on mass was less than it was for density, reflecting a smaller average size of plastic particles after the storm. The average mass of plastic was two and a half times greater than that of plankton, and even greater after the storm. The spatial pattern of the ratio also differed before and after a storm. Before the storm, greatest plastic to plankton ratios were observed at two stations closest to shore, whereas after the storm these had the lowest ratios.     

A comparison of neustonic plastic and zooplankton at different depths near the southern California shore

Previous studies of neustonic debris have been limited to surface sampling. Here we conducted two trawl surveys, one before and one shortly after a rain event, in which debris and zooplankton density were measured at three depths in Santa Monica Bay, California. Surface samples were collected with a manta trawl, mid-depth samples with a bongo net and bottom samples with an epibenthic sled, all having 333 micron nets. Density of debris was greatest near the bottom, least in midwater. Debris density increased after the storm, particularly at the sampling site closest to shore, reflecting inputs from land-based runoff and resuspended matter. The mass of plastic collected exceeded that of zooplankton, though when the comparison was limited to plastic debris similar to the size of most zooplankton, zooplankton mass was three times that of debris.     

Planktoneustonic algae in the surface films of Lake Zürich: Occurrence and dependence on phytoplankton succession

Samples of surface films and of the underlying bulk water at 0.2 m depth were taken in Lake Zürich on 48 occasions in 1986, 1988 and 1989, with the aim of assessing the appropriateness of applying existing neuston nomenclature to the organisms found in these films, of determining which organisms accumulate there during which periods of time, and of assessing the importance of the phytoplankton community in the development of neustonic biocoenoses. Lake Zürich surface films were found to support a community of high population density, consisting of organisms which had migrated from the benthal or pelagial, or which had entered the film via the atmosphere or inflowing rivers. In all samples, species originating from within the phytoplankton community accounted for the greatest proportion of the total abundance. Several of these species were found to exhibit a special preference for the surface biotope, viz. those with a relative frequency (rF) exceeding 10%, a mean enrichment factor (Ef) exceeding 100, and, in the majority of cases, with a greater concentration of individuals in the surface film than in the underlying bulk water layer. We suggest that only those organisms occurring in the surface films of large water bodies which fulfil the above criteria should be considered as belonging to the planktoneuston, in order to distinguish them from other species, the occurrence of which in surface films is merely coincidental. The fact that planktoneustonic algae are dominant in the surface films of Lake Zürich means that changes in the species composition of the planktonic algal biocoenosis directly affect the species composition of the neustonic algal biocoenosis. Thus, just as in the underlying bulk water, a succession can be observed in the algal biocoenosis of the surface films. However, because of the higher abundance of planktoneustonic algae there, this succession is distinct from that occurring in the pelagial. Factors bringing about these differences which are discussed for the case of the dominant planktoneustonic algae are: alterations in specific gravity; positive phototaxis; and enhancement of growth rates in surface films as compared with the underlying bulk water.