The appearance of marine debris (or marine litter) in the ocean is attributed to either the accidental or deliberate introduction of human discarded waste into earth’s waterways, in the form of metals, rubber, paper, textiles, derelict fishing gear and the most abundant debris, consumer plastics. The situation regarding the abundance of anthropogenic debris found in the marine environment has become a widely discussed topic within environmental and scientific communities in recent years, with the major concerns relating to the time period that various debris items take to decompose in the ocean and the physiological and ecological impacts that this waste can have on marine life. In a review of the current state of the oceans regarding marine litter conducted by the United Nations Environment Programme, the scale at which our oceans are being polluted was estimated. It is thought that about 6.4 million tons of marine litter are disposed in the oceans and seas each year. According to other estimates and calculations, some 8 million items of marine litter are dumped in oceans and seas every day, approximately 5 million of which (solid waste) are thrown overboard or lost from ships. Furthermore, it has been estimated that over 13,000 pieces of plastic litter are floating on every square kilometre of ocean today. This marine litter can blow around; remain floating on the water surface; drift in the water column; get entangled on shallow, tidal bottoms; or sink to the seabed at various depths.
Below is an image produced by the National Oceanic and Atmospheric Administration depicting the estimated decomposition times (how long it takes for the structure of the items to degrade) of the most common marine debris found in the ocean. As you can see, the decomposition rates of many of these debris items are staggeringly large, with glass and plastics lasting overwhelmingly the longest in the ocean. Sturdy and durable plastic does not bio-degrade, it only breaks down physically, and so can persist in the environment for hundreds of years in the form of tiny particles.
In the United Nations Environment Programme marine litter review, the main sources of this debris (both sea and land based) are detailed:
Main sea-based sources of marine litter:
• Merchant shipping, ferries and cruise liners
• Fishing vessels
• Military fleets and research vessels
• Pleasure craft
• Offshore oil and gas platforms
• Aquaculture installations.
Main land-based sources of marine litter:
• Municipal landfills (waste dumps) located on the coast
• Riverine transport of waste from landfills, etc., along rivers and other inland waterways
• Discharges of untreated municipal sewage and storm water (including occasional overflows)
• Industrial facilities (solid waste from landfills, and untreated waste water)
• Tourism (recreational visitors to the coast).
The various negative impacts instigated by this debris on the physiology of marine organisms have been well documented.
Entanglement is a major impact of marine litter, whereby an animal becomes trapped or restricted in some way, often resulting in loss of mobility, starvation, amputation, drowning, smothering and constricted circulation leading to asphyxiation. Certain debris can cause open wounds and abrasions to the animal during entanglement which can be painful and result in infections.
Ingestion of debris items has become a common occurrence for many marine animals, judging by post mortem examinations of various species. For example many species of turtle have been known to consume plastic bags assumingly mistaking them for their primary food source, jellyfish, resulting in likely asphyxiation and death. The stomachs of many species of sea birds, whales and sharks have been found to contain a significant amount of plastics from oral consumption, with tissue damage of the stomach lining and oesophagus resulting from this ingestion.
A recent Convention on Biological Diversity report by Dr Richard Thompson (a lecturer of mine), Sarah Gall and Duncan Bury showed that fatalentanglement in and ingestion of marine debris by marine animals has increased by 40% in the last decade with over half of the 280 papers reviewed documenting entanglement and ingestion, impacting 46,000 individuals and 663 species.
Other negative impacts this debris can have on the marine environment includes smothering of the seabed, disturbance of habitats that can affect whole ecosystems and is also increasingly believed to be a source of accumulation of toxic substances in the marine environment (UNEP, 2005). A study conducted by Dr Browne and Professor Richard Thompson at Plymouth University found that tiny particles of plastic which measure 1mm or smaller (resulting from the physical breakdown of larger plastic items), transferred pollutants and additive chemicals – such as flame-retardants – into the guts of lugworms (Arenicola marina). This process results in the chemical reaching the creatures’ tissue, causing a range of biological effects such as thermal stress and the inability to consume as much sediment.
This abundance of marine litter found in the ocean is no doubt extremely detrimental to the preservation of marine life worldwide and steps are being taken in an attempt to eradicate this threat to the oceans altogether. Beach clean ups are a common occurrence in coastal communities worldwide, where passionate volunteers scour the coast removing man-made debris. For example, Ocean Conservancy are responsible for organising the International Coastal Cleanup, which has proved to be extremely successful in keeping coastal areas debris-free. In the 2013 International Coastal Cleanup, 648,015 volunteers in 92 countries picked up more than 12.3 million pounds of trash. However, it is reminded by Nicholas Mallos, Marine Debris Specialist of Ocean Conservancy that the Cleanup alone will not suffice; where he refers to the event as a ‘Band-Aid and not an ultimate cure’ to the long-term threat of marine debris.
As an entirely human made and preventable problem, marine litter must be tackled through deconstructing the issue of marine debris into its primary components (e.g. ingestion of plastics, entanglement in fishing gear, etc.) and then devise and implement specific solutions to tackle each of these. Such solutions will most likely have a major focus on recycling, through reducing the amount of ‘trash’ that is discarded by humans by reusing the material, thus making sure it never reaches the ocean. Better waste management on land and at sea as well as education and awareness-raising activities to influence behaviours could also prove significantly successful in preventing further desecration of the oceans. The disposal of waste products in a manner that is as safe as possible for both the enivronment and human health would also prove succesful, and as detailed in (UNEP, 2005), research and development projects are carried out with the objective to develop plastic packaging material that can be degraded (e.g., by bacteria, or under the influence of UV light). It is noted that creating environmentally-friendly litter could promote the wrong message however, and that a solution that prevents waste reaching the ocean altogether would be a more permanent alternative to this worldwide problem. To find out how you can help to prevent plastics and other waste items reaching the ocean, click here.
For more information regarding the situation of our plastic oceans, see below:
Impact of Marine Debris on Biodiversity, 2012 – http://www.cbd.int/doc/publications/cbd-ts-67-en.pdf