Plastic is one of the biggest threats to the future of coral reefs after ocean warming, say scientists.
“Plastic is one of the biggest threats in the ocean at the moment, I would say, apart from climate change,” said Dr Joleah Lamb of Cornell University in Ithaca, US.
“It’s sad how many pieces of plastic there are in the coral reefs…if we can start targeting those big polluters of plastic, we can hopefully start reducing the amount that is going on to these reefs.”
More than 11 billion items of plastic, inlcuding bags, bottles and rie sacks, were found on a third of coral reefs surveyed in the Asia-Pacific region and this figure is predicted to increase to more than 15 billion by 2025, as stated in a report by BBC News.
Plastic raises by 20-fold the risk of disease outbreaks on coral reefs, according to research. Plastic promotes “colonisation by pathogens implicated in outbreaks of disease in the ocean.”
Coral reefs are essential to people and wildlife for many reasons. In addition to sheltering untold numbers of baby fish and other marine life, they help provide food for more than 275 million people. Reefs are also buffers that protect coasts from storm surge during events such as hurricanes and are a source of billions of dollars in tourism income worldwide every year.
It’s thought that plastic allows diseases that prey on the marine invertebrates that make-up coral reefs to flourish. Branching or finger-like forms of corals are most likely to get entangled in plastic debris.
“A lot of times we come across big rice sacks or draping plastic bags,” said Dr Lamb, who led the study.
“What we do find is these corals with a lot of complexity like branches and finger-like corals will become eight times more likely to be entangled in these types of plastics.”
In the study, published in the journal Science, international researchers surveyed more than 150 reefs from four countries in the Asia-Pacific region between 2011 and 2014.
Plastic was found on one-third of the coral reefs surveyed. Reefs near Indonesia were loaded with most plastic, while Australian reefs showed the lowest concentration. Thailand and Myanmar were in the middle.
“The country’s estimated amount of mismanaged plastics – so the way they deal with their plastic waste – was a strong predictor of how much we would see on the reef,” said Dr Lamb.
The threat of disease from plastic adds to numerous threats already faced by this valuable resource. Corals are experiencing bleaching events that sicken and kill them in warming waters from climate change. They are being slowly poisoned by chemicals in sunscreen that humans lather on before snorkeling to them. Acids from human-emitted carbon dioxide that the ocean absorbs is also breaking down coral. Even ravenous, predatory sea stars, also known as starfish, prey on them.
In the case of diseases, organisms attack coral, leading to likely death. Previous research has found that plastic debris can stress coral by blocking out light and oxygen, thereby giving pathogens a chance to take hold.
Drew Harvell, a professor of marine ecology at Cornell and one of the study’s 11 authors said, “I kind of think of plastic as a triple whammy for coral. First it cuts open the skin of the coral, and then it can convey pathogenic microorganisms, and finally, it can shade the light coral needs and cut off water flow.”
Based on projections of plastic waste going into the ocean, the researchers suggest that the number of plastic items snagged on Asia-Pacific corals may increase from 11.1 billion to 15.7 billion plastic items by 2025.
An estimated 4.8 to 12.7 million tonnes of plastic waste enter the ocean in a single year.
More than three-quarters of this plastic is thought to originate on land.