Sea-Surface Slicks and Their Effect on the Concentration of Plastics and Zooplankton in the Coastal Waters of Rapa Nui (Easter Island)

Abstract

The abundance and distribution of plastic debris at the sea surface shows considerable variability over different spatial scales. Some of the oceanographic processes at small (<1 km) and submeso (1–10 km) scales manifest themselves as slicks at the sea surface, which might have the potential to concentrate organisms and particles (such as positively buoyant plastics), putting species that feed in these areas at risk of ingesting plastics. Slicks can be filaments, lines, meanders, or patches, which are lighter in color and smoother in surface roughness compared to the surrounding area. Here we tested the hypothesis that passive particles (including plastics) and organisms are aggregated in the surface waters within these slicks. According to their main features (orientation to coast and/or wind), the studied slicks were most likely generated by oceanographic processes such as topographically controlled fronts, other types of fronts and internal waves. Neuston samples were collected from the sea surface inside and outside of slicks (n = 11 sites with slicks) in the coastal waters of Rapa Nui (Easter Island) during two campaigns in austral summer (January 2018) and autumn (April 2019). In general, passive particles, including plastics, exuviae, eggs and foraminiferans, were found more frequently inside than outside the slicks. In some cases, motile zooplankton organisms such as chaetognaths, vertically migrating crustaceans and early developmental stages (EDS) of fish were also more common within the slicks. In addition, a positive relationship was found between plastics and planktonic organisms such as foraminiferans, snails and jellyfish (e.g., Velella velella), although a strong correlation was also found with fish EDS and chaetognaths. These results suggest that surface slicks are areas of aggregation for both passive particles and active organisms, thus playing an important ecological role in food retention and particle concentration where the risk of plastic ingestion by fish and seabirds is enhanced.

Selective foraging behavior of seabirds in small‐scale slicks

“…In conclusion, our results support our prediction that terns select slicks for foraging. Future studies evaluating the prevalence, benefits, and risks associated with marine predator foraging within slicks would also benefit from concurrent in situ sampling as done elsewhere (Stevick et al 2008;Young and Adams 2010;Gove et al 2019;Gallardo et al 2021;Whitney et al 2021). This integration of remote sensing approaches and statistical analyses of high-resolution tracking data in combination with in situ sampling will improve our understanding of marine species interactions with small-scale dynamic features, allowing better predictions of species' responses to a changing ocean.…”

“…Apart from accumulating flotsam, slicks have been shown to host higher concentrations of zooplankton, meroplankton, and small fish compared to ambient water (Shanks 1983;Kingsford and Choat 1986;Gade et al 2013;Weidberg et al 2014;Whitney et al 2021). There is also growing evidence that slicks concentrate plastics (Gove et al 2019;Gallardo et al 2021), raising concerns about plastic ingestion (direct or indirect) by seabirds foraging within slicks (Young and Adams 2010).…”

Hotspots of Floating Plastic Particles across the North Pacific Ocean

“…68 This observation may result from meso-and sub-mesoscale accumulation mechanisms, such as surface windrows and slicks. 39,69 The high share of plastic items in the size range of 330−500 μm in the sample from the PMNM (Figure S8), one of the largest marine conservation areas in the world, where other environmental stressors already threaten biodiversity, highlights potential ecological repercussions. These rather small plastic items are more likely to be ingested by a wider range of species and tend to more rapidly sorb or desorb chemical additives, pollutants, and pathogens because of their higher surface-to-volume ratio.…”

Natural and oil surface slicks as microbial habitats in marine systems: A mini review

“…Bacterioneuston community composition sometimes differs from the underlying bacterioplankton community, in particular among the particle-attached bacterial fraction and under slick or slick-like conditions (Stolle et al, 2010;Rahlff et al, 2019), while other studies described more similar community structures of neuston and plankton (Stolle et al, 2011;Zäncker et al, 2018). Overall, surface slicks are an important biological habitat, accumulating different marine organisms (Gallardo et al, 2021). Slicks aid distribution of algae, meroplanktonic larvae, and small fish (Shanks, 1983;Kingsford and Choat, 1986;Weidberg et al, 2014), act as nurseries for neustonic larval fishes and zooplankton (Whitney et al, 2021), and provide shelter and prey to different animals (Kropach, 1971;Whitney et al, 2021).…”

“…Capone et al (1998) described that natural slicks can cover a surface area of 1300 m 2 . Slicks can be a warmer, less saline, and a more viscous environment compared to surrounding waters, and they often carry sea weeds like Sargassum sp., particulates including plastics, and foams (Dietz and Lafond, 1950;Carlson, 1987;Gower et al, 2006;Wurl et al, 2016;Wurl et al, 2018;Gallardo et al, 2021). The lifespan of natural slicks typically lasts for several hours (Marmorino et al, 2008), but reformation of slicks after periods of strong winds is possible within an hour (Hardy, 1991).…”