Marine debris

2016

Within the marine environment, marine debris is sourced from both the land (rubbish flushed out to sea; see further detail on coastal pollution in the Coasts report) and marine industries (loss of equipment, often from fishing operations). Although marine debris can be found in all areas of the marine environment in the Australian EEZ (see Box MAR4), northern Australia is especially vulnerable because of the proximity of intensive fishing operations (including international operations) to the north of Australia, regional difficulties in surveillance and enforcement, and ocean circulation and wind patterns that appear to promote accumulation of floating debris (Kiessling 2003).

Entanglement of marine animals in debris can cause restricted mobility, drowning, starvation, smothering, wounding and amputation of limbs—all of which can result in death. One of the major threats to marine wildlife through entanglement is ghost nets. These are fishing nets that drift through the ocean unattended for years or even decades, ‘ghost fishing’ and entangling and killing commercially valuable or threatened species (Laist 1987, 1997, Macfayden et al. 2009). To date, more than 13,000 nets have been removed from beaches and estuaries by organisations such as GhostNets Australia. Surveys of ghost nets in the northern Australian region found that, of the approximately 50 per cent that could be identified, only 4 per cent originated from Australian fisheries (Gunn et al. 2010).

Floating plastics are also a major threat because they are resistant to breakdown, and thus persist and accumulate in the marine environment. Many are ingested by marine animals, and remain in the stomach and accumulate, eventually causing starvation. Plastics are also a potential source of toxic chemicals (Lavers et al. 2014). These chemicals, once leached out of the ingested material and transferred into the blood and tissues of individuals, may cause sublethal health effects in wildlife, even at very low contamination levels (Tanaka et al. 2013). Marine life as small as plankton is affected by debris in the form of ‘microplastics’ (less than 5 millimetres in diameter), which are a widespread and ubiquitous contaminant of marine ecosystems across the globe. This form of marine debris has been reported as causing decreased feeding because of ingestion, and reduced mobility because of adherence to the external carapace and appendages of exposed zooplankton (Cole et al. 2013). Microplastics have also been linked to the degradation of molecular, cellular, physiological and, ultimately, ecological processes within the marine environment (Browne et al. 2015).

Data on the distribution of debris at sea are scarce, largely because of the expense of collecting these data, which requires use of aircraft or vessels. Some progress has been made in predicting the distribution of marine debris at sea (see Wilcox et al. 2013, 2015; Eriksen et al. 2014), which was surveyed for the first time in Australian waters in 2013 (Hardesty et al. 2014).

Despite initiatives banning the use of some plastic products, the use of plastics continues to grow globally. As a result, the pressures being placed on the marine environment by dumped, discarded and lost debris continue to increase (Jambeck et al. 2015). This was reflected in a review of the threat abatement plan for the effects of marine debris on vertebrate marine life (DEWHA 2009a), which concluded that the objectives of the plan had not been met and the plan needed to be revised (DoE 2015b). Impacts on the marine environment associated with marine debris are high, with a deteriorating trend.

Box MAR4 Marine debris

Marine debris is recognised as a globally important pressure in the marine environment, with increasing reports of impacts on marine biodiversity reported during the past 4 decades (Gall & Thompson 2015). Debris entering the marine environment can include consumer items such as glass and plastic bottles, aluminium and metal cans, plastic bags, balloons, rubber, metal, fibreglass, cigarettes, and microbeads included in personal care products. Marine debris can range in size from multitonne fishing nets to microscopic pieces of plastic that have broken down from their original size. Marine debris includes those materials that are transported from the land into coastal environments and the ocean, as well as materials intentionally or unintentionally discarded at sea. It is estimated that more than 6–12 million tonnes of plastic waste enter the oceans each year (Jambeck et al. 2015).

In Australia, marine debris has been identified as a key threatening process for threatened and endangered vertebrate fauna. Around three-quarters of items found on Australian beaches are plastic polymers (Hardesty et al. 2014). Marine debris also has socio-economic impacts: it transports species (introduced or native) and can be a navigation hazard. There are also increasing concerns about the risks to human health, because of the accumulation of pollutants in the tissues of seafood species that have ingested marine debris (Rochman et al. 2015). High but variable concentrations of marine debris are found in all marine environments (Hardesty et al. 2014, Critchell et al. 2015, Critchell & Lambrechts 2016), and it is expected that marine debris will continue to be a ubiquitous problem because of the continued growth in the production and use of plastics.

Key components of the marine environment affected by marine debris

Marine fauna as small as plankton and as large as whales are known to interact with marine debris (Vegter et al. 2014). Entanglement, ingestion and chemical contamination are the 3 main types of interaction (Wilcox et al. 2015). Corals, lugworms, molluscs, commercial fish (Hall et al. 2015, Rochman et al. 2015), seabirds (Acampora et al. 2013, Verlis et al. 2013), sea turtles (Schuyler et al. 2013, Wilcox et al. 2013), sea snakes (Udyawer et al. 2013), pinnipeds (Page et al. 2004, Lawson et al. 2015), dugongs (GBRMPA 2014a), whales (Evans et al. 2002, Hammer et al. 2012) and dolphins (Chatto & Warneke 2000) are all reported to be affected by marine debris. Significant quantities of plastics have been reported in the digestive tracts of several species of marine vertebrates in Australian waters.

Major uncertainties and knowledge gaps

A recent circumnavigation of Australia during which floating plastics were recorded found concentrations as high as 40,000–80,000 pieces per square kilometre, but more commonly ranging from 1000 to 40,000 pieces per square kilometre. This was the first survey of its kind, and it highlights both the variability of plastics in the marine environment and the lack of consistent, large-scale monitoring (Hardesty et al. 2014). Data from this project have contributed to a global assessment that modelled the distribution of plastics in the marine environment (Figure MAR21). This global assessment identified that, although the waters around Australia contained lower concentrations of small (0.33–1.00 millimetres) items of marine debris, concentrations of larger (more than 1.00 millimetre) items of marine debris in some locations around Australia were comparable to those measured in other parts of the world (Eriksen et al. 2014).

Major uncertainties persist with regard to:

  • population-level impacts of marine debris from entanglement of, and ingestion by, marine fauna, including sea turtles, marine mammals, seabirds, and commercially and recreationally caught food fish
  • the frequency and potential economic impact of transport of species on marine debris
  • changes (or trends) in debris distribution, origins and losses into the environment
  • the cost of marine debris to fisheries and small businesses in Australia
  • the potential impact of ingested plastics on human health from seafood.

Outlook

The amount of debris entering the marine environment is expected to increase, with a corresponding increase in impacts on the marine environment, and an associated increase in socio-economic, environmental, navigation and hazard impacts. Policies are currently under consideration or have been implemented across local council, state and territory, Australian Government, and international jurisdictions that aim to reduce the amount of debris entering the oceans and affecting wildlife (including plastic bag bans, container deposit schemes, and bans on microbeads in personal care products). A sustained, multifaceted approach that involves manufacturing industries, consumers, recycling, infrastructure, litter traps, and coastal and inland clean-up activities, as well as education, outreach and awareness raising, is required to reduce debris in the marine environment.

Evans K, Bax NJ, Smith DC (2016). Marine environment: Marine debris. In: Australia state of the environment 2016, Australian Government Department of the Environment and Energy, Canberra, https://soe.environment.gov.au/theme/marine-environment/topic/2016/marine-debris, DOI 10.4226/94/58b657ea7c296