Plastic pollution is rife even in deep coral reefs, with most coming from the fishing industry.
Studies suggest that plastic makes up 80 per cent of all ocean debris. Marine life can become entangled in this and experience severe distress, says Lucy Woodall at the University of Exeter, UK. Fish are also ingesting plastics at a growing rate.
But while plastic pollution has been widely studied in oceans, its prevalence at coral reefs specifically has been less extensively analysed, says Woodall. Many of these habitats are deep in the ocean and so are hard to access, she says. “If we only look on the surface then we’ll be missing a really important component,” says Woodall.
To investigate, Woodall and her colleagues collected water samples from 84 coral reefs from 25 sites across the Pacific, Atlantic and Indian oceans. Some of these reefs are considered shallow, less than 30 metres deep, while others are 30 to 150 metres down. The samples were collected by divers and crewed and remotely controlled submersibles.
The researchers found that 92 per cent of the ecosystems they analysed were contaminated by artificial debris measuring more than 5 centimetres across, of which 88 per cent was plastic.
Just one location, the outer islands of the Seychelles in the Indian Ocean, was totally free of this debris. These islands, some of which are UNESCO World Heritage sites, are carefully managed by officials, says Woodall. “It shows that when areas are afforded protection and when they are remote, it is possible to have a positive story.”
For the remaining sites, the densities of plastic found ranged from 500 to 90,000 items per square kilometre. Most of this came from fishing, with the pollution being worse at greater depths. “As you go down, things accumulate,” says Woodall. “What we’re seeing here is an accumulation of plastic over time.”
Overall, the coral reefs located close to Comoros off the east coast of Africa had the worst plastic pollution, consisting mainly of household items. “There isn’t really an effective waste management system on the islands and so people have no other option but to dump their waste into the ocean,” says Woodall.
“Evidence on the extent and impacts of plastic pollution is essential to help prioritise the need for action,” says Richard Thompson at the University of Plymouth, UK. More studies now need to look at how best to solve plastic pollution in oceans, he says.