Coral reefs are under attack — not by water, fish or underwater creatures, but by man and his inventions. According to a new report by Science Magazine, our plastic creations are causing some of the world's most important natural underwater life structures to become infected with disease.
Scientists who conducted the reef survey examined 159 coral reefs spanning eight latitudinal regions from four countries in the Asia-Pacific region, which contains 55.5 percent of global coral reefs and encompasses 73 percent of the global human population residing within 50 kilometers of a coast.
Overall, scientists documented plastic waste (defined as an item with a diameter greater than 50 mm) on one-third of the coral reefs surveyed. The number of plastic items observed on each reef varied markedly among countries. Indonesia was the worst offender, while Australia had the cleanest reefs.
According to the scientists, plastic waste can "host pathogens that are frequently implicated as triggers of disease outbreaks on coral reefs. For example, microbial communities colonizing polypropylene marine debris were dominated by the genus Vibrio, an opportunistic pathogenic bacteria of a globally devastating group of coral diseases known as white syndromes. Although an estimated 4.8 million to 12.7 million metric tons of plastic waste enter the ocean in a single year, the resulting influence on disease susceptibility in the marine environment is unknown."
Thus, the coral reef ecosystem has a high levels of colonized plastic waste. The Asia-Pacific region encompasses nine of 10 countries with the highest global levels of mismanaged plastic waste entering the ocean. Projections of plastic debris on coral reefs for Indonesia and China in 2025 were set to the maximum from 2010, owing to the limitations of the model range.
The study examined the influence of plastic waste on disease risk in a marine organism, in which scientists visually examined 124,884 reef-building corals for signs of tissue loss characteristic of active disease lesions.
When corals were not in contact with plastic debris, the likelihood of disease was 4.4 (± 0.2) percent across all eight regions, the scientists reported. In contrast, in the presence of plastic debris, the likelihood of disease occurrence in corals was more than 20 times higher at 89.1 (± 3.2) percent
Human population size in coastal regions and the quality of waste management systems largely determine which countries contribute the greatest plastic loads entering the ocean, given that an estimated 80 percent of marine plastic debris originates from land.
By 2025, the cumulative quantity of plastic waste potentially entering the marine environment from land is predicted to increase by one order of magnitude. "Using this projection and assuming that the area encompassed by coral reefs remains constant, we estimate that 15.7 billion plastic items will be entangled on coral reefs across the Asia-Pacific by 2025," the scientists said.
Given the widespread distribution of plastic debris on coral reefs and the consequent increased likelihood of coral mortality from disease, scientists evaluated the potential for plastic debris and disease to affect structural complexity provided by habitat-forming corals.
The structural complexity formed by corals "underpins the availability of microhabitats for coral reef-associated organisms. We grouped coral species into three broad classifications based on the increasing structural complexity of their colony morphologies (massive < branching < tabular) and determined that plastic debris is eight times more likely to affect reef corals with greater structural complexity," they wrote.
Widespread distribution of plastic waste may have negative consequences for biodiversity and people. For example, on coral reefs, the loss of structural habitat availability for reef organisms has been shown to reduce fishery productivity by a factor of three.
With more than 275 million people relying on coral reefs for food, coastal protection and tourism income, moderating disease outbreak risks in the ocean will be vital for improving both human and ecosystem health.
"Our study indicates that decreasing the levels of plastic debris entering the ocean by improving waste management infrastructure is critical for reducing the amount of debris on coral reefs and the associated risk of disease and structural damage," the study authors wrote.
