Monitoring the abundance of plastic debris in the marine environment

Abstract

Plastic debris has significant environmental and economic impacts in marine systems. Monitoring is crucial to assess the efficacy of measures implemented to reduce the abundance of plastic debris, but it is complicated by large spatial and temporal heterogeneity in the amounts of plastic debris and by our limited understanding of the pathways followed by plastic debris and its long-term fate. To date, most monitoring has focused on beach surveys of stranded plastics and other litter. Infrequent surveys of the standing stock of litter on beaches provide crude estimates of debris types and abundance, but are biased by differential removal of litter items by beachcombing, cleanups and beach dynamics. Monitoring the accumulation of stranded debris provides an index of debris trends in adjacent waters, but is costly to undertake. At-sea sampling requires large sample sizes for statistical power to detect changes in abundance, given the high spatial and temporal heterogeneity. Another approach is to monitor the impacts of plastics. Seabirds and other marine organisms that accumulate plastics in their stomachs offer a cost-effective way to monitor the abundance and composition of small plastic litter. Changes in entanglement rates are harder to interpret, as they are sensitive to changes in population sizes of affected species. Monitoring waste disposal on ships and plastic debris levels in rivers and storm-water runoff is useful because it identifies the main sources of plastic debris entering the sea and can direct mitigation efforts. Different monitoring approaches are required to answer different questions, but attempts should be made to standardize approaches internationally.

Neustonic microplastic and zooplankton in the North Western Mediterranean Sea

“…The samples were collected with a manta trawl net lined with 0.333 mm mesh (Ryan et al, 2009). The size of the rectangular net opening was 0.6 Â 0.2 m 2 .…”

“…Microplastics are accumulating at the sea surface, especially within the neustonic habitat (Ryan et al, 2009). This habitat harbors a diverse and specifically adapted zooplankton fauna.…”

“…Moreover, it is probable that a wide range of marine organisms are affected by plastic wastes in the sea. Macrodebris ingestion and entanglement are well documented in sea birds, mammals and turtles and more recently in fishes and invertebrates (e.g., Laist, 1987Laist, , 1997Gramentz, 1988;Weisskopf, 1988;Slip et al, 1990;Moser and Lee, 1992;Shaw and Day, 1994;Goldberg, 1997;Robards et al, 1995;Derraik, 2002;Thompson et al, 2004;Ryan et al, 2009;Boerger et al, 2010;Murray and Cowie, 2011).…”

Marine debris: A proximate threat to marine sustainability in Bootless Bay, Papua New Guinea

“…While most studies of intertidal debris have used transects with a minimum length of 50 m (e.g. Ryan et al, 2009), the sheer density of debris at some sites precluded this approach. Instead, sampling was done with relatively small sampling units (1 x 2 m quadrats) which were replicated within each site (n = 5 at each site; note that greater replication (n = 8) occurred at the sites with the densest debris loads -sites 1, 2 and 20 - Fig.…”

Ingestion of Microplastic Has Limited Impact on a Marine Larva

“…The growing use of synthetic materials is increasing the prevalence of plastic in the marine environment 1 . It is estimated that 10 % of the 280 million tonnes of plastic produced annually worldwide ends up in the ocean, contributing to 60 -80 % of all marine debris [2][3][4] .…”