Plastic in the marine environment

Plastic - the waste that nature cannot digest. Millions of tonnes of rubbish enter the worlds oceans each year killing marine mammals and seabirds.

Plastic in the marine environment

If someone had suggested a hundred years ago that humankind would set about to create a material so resilient and pervasive that it would become a toxic unsightly legacy that would help push individual species to the brink of extinction and seriously undermine entire ecological systems, we would have thought they were joking. Of course such a scenario was never the intention.  It is, however, today's reality.

While the issue of plastic supermarket bags and plastic bottles continues to be handballed around the political arena more than 1 million marine animals die every year from entanglement in or ingestion of a whole range of anthropogenic debris, mostly plastics and other synthetic substances. Due to the recent publicity surrounding the staggering quantities of plastic waste trapped in the North Pacific Subtropical Gyre the concern about the amount of plastic waste winding up in the oceans has come to the fore and everyone is asking themselves "how can this happen?" How can an area of ocean fifty times the size of Tasmania be covered in plastic so thick it looks like a solid surface?

Sadly, while the plastic soup in the north Pacific is shocking beyond belief it is a problem that is by no means confined to that area. Ocean and atmospheric currents have combined to capture and hold the waste in that gyre but today almost anywhere on earth a scientist can examine a cup of sand or seawater and find a range of plastics in a variety of sizes. So how does this happen?

  • No one can say exactly how much plastic has been manufactured since its invention but one thing is known for sure - all of it is still with us. Plastic is not biodegradable. Organic material such as food scraps or paper will eventually break down to become carbon dioxide and water. Plastic on the other hand is bio-inert, ie. It is chemically very stable and will not degrade like naturally occurring materials. Instead it will be progressively weakened by sun and sea until it becomes brittle and breaks up into increasingly smaller pieces. But it will not reduce to carbon dioxide and water
  • We use way too much plastic. Our food packaging system relies almost entirely on plastic and the common method of marketing other goods means the majority of non-food consumables are also packaged in plastic. In Australia alone more than 700 million litres of bottled water are consumed every year. Each bottle might take on average a couple of minutes to consume but hundreds of years from now the bottle will still be here
  • Plastic is very lightweight and can easily be blown directly into the ocean or make its way there via urban drains, creeks and rivers. In years gone by, many countries also dumped millions of tons of municipal garbage directly into the ocean. While this practice has almost stopped the legacy is enduring to the point that in many areas of the ocean surface plastic outweighs plankton.

The effect of plastic on marine life can be devastating. Minute particles of plastic are consumed by the filter feeder organisms that form the base of the marine food web. This presents two problems in that plastic materials themselves are known to be toxic and they also appear to act as a sponge for other pollutants which are taken up by the filter feeders. As the plastic molecules progress through each trophic feeding level animals at the upper trophic levels, such as birds, fish, marine mammals and sea turtles can accumulate increasingly larger quantities of toxins in their bodies.

Larger pieces of plastic present an additional problem. When plastics, which in the water look remarkably like an animal's natural food, are eaten they clog the animal's digestive system leading to prolonged and painful internal injuries, eventually resulting in death. As the dead animal decomposes the plastic is freed, relatively intact, to be ingested by another marine animal that may again mistake it for food.

Because plastics are extremely variable in their composition, colour and shape they tend to break down to produce an infinite variety of shapes, sizes and colours. This diversity increases the availability to a wider range of organisms. For example, sea turtles can mistake plastic bags for jellyfish; filter feeders (including the larger baleen marine mammals) inadvertently take up large quantities of plastic; and seabirds, particularly surface feeders, ingest large quantities of plastic both directly from the surface and through ingestion of fish and other prey.

What can you do to reduce plastic in the environment?

To most of us the problem seems almost insurmountable when we are confronted with so few alternatives to the plastic packaging that dominates the market today. But what we can do is:

  • tell governments and manufacturers that we have made a mistake and it is a mistake that needs to be urgently rectified.  We need to let them know that it is not acceptable that a chocolate bar that takes 30 seconds to eat is packaged in a wrapper that will persist in the environment for hundreds of years. And it is not okay that a disposable plastic bottle used to hold a drink that can be consumed in minutes will contribute to the already staggering amount of plastic waste littering the planet
  • modify your buying habits, for example avoid products that are over-packaged
  • minimise your use of takeaway food and drink containers, e.g. carry a drink bottle from home in preference to buying bottled water.

Further reading

Seabirds as indicators of plastic pollution in the North Pacific, Hannah Nevins, David Hyrenbach, Carol Keiper, Jenny Stock, Michelle Hester, and Jim Harvey.

Algalita Marine Research Foundation.