Plastic in the oceans

Plastic is everywhere. It is in the things we use daily, but the waste from throw-away single-use plastics is causing a huge pollution problem - as recently highlighted in the BBC Blue Planet 2 programme.

Bits of plastic have been found in every corner of the world, including the deepest ocean trenches and on uninhabited islands. It is estimated that a truckload of plastic enters the ocean every single minute and that UK supermarkets produce 800,000 tonnes every year.

 Plastic pollution is any plastic that ends up in the environment – from bottles and bags to less obvious sources like teabags and clothes. In the oceans, plastics stick around for ages and even as the degrade they shed smaller particles of plastic!

 Fish, seabirds, sea turtles and marine mammals can become entangled in or ingest plastic debris, causing suffocation, starvation and drowning. At least 180 species of marine animals have been documented consuming plastic, from plankton to whales. The stats speak for themselves including:

  •  All seven species of sea turtle are known to ingest plastics;

  • 99% of sea birds could inject plastic by 2050 and 15% of a chick’s body weight could be made up of plastic;

  • 47 species of whale are known to ingest plastics; and

  • Plastic has been found inside the guts of a third of UK-caught fish, including species that we regularly consume as food.

Why do marine animals eat plastics?

A simple explanation is that animals simply mistake plastic for familiar food items – plastic bags, for example, are thought to resemble jellyfish. Marine turtles rely primarily on their vision to search for food. However, they are also thought to possess the capacity to see UV light. Studies at The University of Queensland, Australia, have modelled the visual capabilities of marine turtles measuring the visual characteristics of plastics as turtles see them. The conclusion is that while young turtles are relatively indiscriminate, older turtles preferentially target soft, translucent plastic. The results confirm a long-held idea that turtles mistake plastic bags for delicious jellyfish.

When foraging, many marine animals rely primarily on their sense of smell. Experiments suggest that some species of seabirds and fish are attracted to plastic by its odour. Algae grows on floating plastic and releases a chemical called dimethyl sulfide (DMS) which is eaten by krill which in turn releases DMS. This attracts foraging birds and fish that eat the plastic rather than the krill.

Colour may also play a part in plastic consumption, although research suggests that preference for colour varies between species. Young turtles have been found to be attracted to white plastic, while it has been found that seabirds called shearwaters opt for red plastic.

Echolocation, by toothed whales and dolphins, is thought to misidentify plastic objects as food. These species have been found with huge quantities of plastic in their stomachs.

In the marine environment plastic doesn’t just look like food, it smells, feels and even sounds like food. Our rubbish comes in such a range of shapes, sizes and colours that it appeals to a wide and diverse range of species. This video was taken at Acuario de Sevilla and demonstrates how plastics appear in water – it demonstrates clearly how our rubbish can mimic prey for animals and how easily they can feed upon it.

Stewart Parsons