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Section 1: Impacts of marine debris on biodiversity
An area of growing concern is the accumulation of buoyant debris such as plastic items and microplastic
fragments in the open oceans. Goldstein et al., (2012) determined that the concentration of microplastics within
the North Pacific Central Gyre had increased by two orders of magnitude in the past four decades, similarly,
Law et al., (2010) showed that the greatest abundance of debris in subtropical locations was far from land, and
in a study of the north western Mediterranean, Collingnon et al., (2012) estimated the mean abundance of
microplastics to be the same order of magnitude as that found by Moore et al., (2001) within the North Pacific
Gyre (1.334 particles m -2 ).
Oceanic gyres result from the complex network of currents that circulate water around the oceans, coupled with
the effects of wind and the rotation of the globe. They form slowly rotating current systems in which marine
debris can accumulate. Due to the durability and persistence of some items of marine debris, once it enters
a gyre system it can remain for long periods of time, meaning that the concentration of debris within these
systems can be considerably greater than in other areas of the ocean. Moore et al., (2001), for example, found
densities of plastic of 334,271 pieces km -2 , or 5114 g km -2 , within the North Pacific Subtropical Gyre—the largest
recording of debris in the Pacific Ocean.
1.3 METHODOLOGY
Section 1 of this report reviews the current state of knowledge about the effect of marine debris on ecosystems and
biodiversity. Evidence of the effects of marine debris on species is examined, the number of reported encounters
between individuals and debris and their effects considered and compared with the species’ conservation status
as defined by IUCN, and effects on ecosystems were assessed. Indirect effects such as the facilitation of transport
of invasive species and the potential provision of novel habitats provided by marine debris are also considered.
Impacts are considered under four broad headings:
1) Ingestion and entanglement
2) Provision of new habitat—potential for debris to
provide new habitats
3) Dispersal via rafting, including transport of
invasive species
4) Ecosystem level effects
Data in peer reviewed publications and reports in grey literature. Literature was identified using electronic
keyword searches using Web of Science, Google Scholar and Google. Keywords for debris included: marine
debris, floating marine debris, marine litter, debris, plastic, metal, glass, and paper, together with key words for
effects including: impact, entanglement, ingestion, ecosystem, habitat, biodiversity, rafting, invasive and alien.
Limitations in the data collection process are outlined in Annex 2.
The reference list from an extensive review by Laist (1997) was also revisited and all traceable sources used.
Where papers referenced other studies that had not already been captured, they were examined and included
where relevant. A species list was then compiled, and additional species-specific searches conducted for each
of the aforementioned effect terms to ensure that coverage was as extensive as possible. Contact by e-mail was
made with key researchers and the coordinators of UNEPs Regional Seas Programmes to identify additional
data, and in particular, grey literature.
Each report and publication was examined and information extracted in relation to documented encounters
between marine debris and an organism. This information is outlined in Annex 1. Data on species affected
by marine debris was then cross referenced with the IUCN Red List in order to establish the extent to which
endangered or vulnerable species were implicated.
For reports of species rafting on marine debris, and the use of marine debris as habitat, data were extracted
as described above. Numbers of individuals, however, was not commonly reported, and consequently was not
included in the analysis. Type of harm was also not relevant here.
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