Fishing gear plastic found to cause most of coral reef plastic pollution

Fishing gear plastic formed nearly three-quarters of the plastic debris documented through underwater visual surveys of coral reefs across the Indian, Pacific, and Atlantic oceans, new research published in the journal Nature said.

Revealing the extent of plastic pollution on coral reefs, an international team of researchers from the California Academy of Sciences (US), University of Sao Paulo (Brazil), University of Oxford (UK), and other collaborators found that debris increased with depth and is correlated with proximity to marine protected areas.

The team conducted more than 1,200 visual surveys across 84 shallow and mesophotic reef ecosystems located in 14 countries. Mesophotic, or ‘twilight zone’, coral reefs exist between 30 and 150 metres deep.

Of the total debris, 88 per cent was macroplastics larger than about five centimetres.

Human-derived debris was found in nearly all locations studied, including some of the planet’s most remote and pristine coral reefs, such as those adjacent to uninhabited islands in the central Pacific.

The lowest density of plastic pollution was seen in the Marshall Islands, a coral island group in eastern Micronesia (Oceania), while the highest was recorded at Comoros, an island chain off the southeast coast of Africa, at nearly 84,500 items per square kilometre.

The study found coral reefs to be more contaminated by plastics than other marine ecosystems that were evaluated, and that the contamination, increasing with depth, peaked in the mesophotic zone.

“It was surprising to find that debris increased with depth since deeper reefs in general are farther from sources of plastic pollution,” said Luiz Rocha, Academy curator of ichthyology, and senior author on the study.

“Fishing gear, which even as debris continues to catch marine life through what we call ghost fishing, appears to contribute a large proportion of the plastic seen on mesophotic reefs,” said co-author Lucy Woodall, associate professor in marine conservation biology and policy at University of Exeter, UK.

“Unfortunately, fishing gear debris is often not reduced by general waste management interventions; therefore specific solutions related to the needs of fishers should be considered, such as no-charge disposing of damaged gear in ports or individually labelling gear to ensure fishers take responsibility for misplaced equipment,” said Woodall.

“From macroplastics that spread coral diseases to fishing lines that entangle and damage the structural complexity of the reef, decreasing both fish abundance and diversity, pollution negatively impacts the entire coral reef ecosystem,” said Hudson Pinheiro, the study’s lead author and a biologist at the University of Sao Paulo.

“As marine resources around the world dwindle, humans that rely on those resources are turning to deeper habitats and those closer to marine protected areas where fish remain abundant,” said Pinheiro.

The researchers hoped that conservation efforts can be redirected to better protect and ensure a thriving future for Earth’s coral reefs.

“The results of our global study shine a light on one of the many threats that deep reefs face today,” said study author and University of Oxford marine biologist Paris Stefanoudis. “Because these ecosystems are ecologically and biologically unique, much like their shallow-water cousins, they need to be conserved and explicitly considered in management plans.”