Tiny pieces of plastic cause 'gangrene' on coral reefs

Submerged plastic can sicken coral

Submerged plastic can sicken coral. Courtesy of Richard Whitcombe Alamy

The study estimates 11.1 billion plastic pieces are entangled on reefs just in the Asia-Pacific region alone, and the number is projected to increase 40 percent by 2025.

"Our work shows that plastic pollution is killing corals", said senior author Professor Drew Harvell, an ecologist at Cornell. "So moderating disease outbreak risks in the ocean will be vital for improving both human and ecosystem health", Willis added.

In order to assess how much plastic there is in the reefs, worldwide researchers surveyed more than 150 reefs for four years (from 2011 to 2014). "This is associated with the globally devastating group of coral diseases known as white syndromes", said Dr Lamb. Stress caused by the presence of plastic debris also makes it more hard for corals to fight off pathogens.

"What's troubling is that once the coral tissue loss occurs, it's not coming back..."

"Its like getting gangrene on your foot and there is nothing you can do to stop it from affecting your whole body", the researcher said. In December (2017), nearly 200 nations agreed to limit plastic pollution of the oceans, warning that it could outweigh all fish by 2030.

Finally, plastic debris overtopping corals can block out light and create low-oxygen conditions that favour the growth of microorganisms linked to black band disease.

This year has already seen a United Kingdom ban on the manufacture of products containing tiny fragments of plastic called microbeads, as well as debate over the future of disposable coffee cups and plastic bottles.

Coral reefs are already being assailed by catastrophic "bleaching" events along with over-fishing and attacks by ravenous starfish but now man-made plastics are being highlighted as threat because they can introduce disease into the delicate eco-systems.

The study, which was led by Joleah Lamb of Cornell University, is the culmination of years of surveying dozens and dozens of coral reefs.

As well as documenting the plastic waste they saw, the scientists visually examined almost 125,000 corals, looking for evidence of disease. Plastic tumbling along in the ocean causes small cuts in the corals, which exposes them to diseases, increasing the likelihood that they will get sick from 4% to an astonishing 90%.

She said very few studies have examined the role plastics could play in promoting disease in the marine environment. Turtles and fish can mistakenly eat plastic debris and it's estimated that more than 1 million seabirds die each year from ocean pollution and ingestion or entanglement.

"Bleached coral is more susceptible to disease", Harvell says.

Based on other studies, the researchers think there are a couple of ways the plastic could be causing disease.

The more they looked, especially in Asian waters, the more they found: Bottles, diapers, Q-tips, food wrappers.

Corals have a symbiotic relationship with a tiny marine algae called "zooxanthellae" that live inside and nourish them.

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