Fabrics, storage containers, carrier bags and even airplanes – plastics have revolutionized our lives since the mass production of plastic polymers began in the 20th century. It is estimated that 9.1 billion tons of plastic was produced worldwide between 1950 and 2015, with only 10% of global production being recycled. The remaining 90% has steadily accumulated in the environment, especially in the oceans, where 5-13 million tons of plastic are discarded every year.

Sometimes referred to as the 7th continent, it is estimated that 270 000 tons of plastic float on the surface of our oceans. The direct impact of plastics on marine life is well documented: turtles, seabirds and marine mammals often die after ingesting plastic residues. Every year, plastic pollution kills an estimated 1.5 million animals. Images of sea turtles eating plastic grocery bags and whales washing up onshore with plastic in their guts have circulated for years, and although the direct impact of plastic ingestion by marine animals is well understood, the impact of plastics on reef-building corals had been largely ignored until recently, perhaps due to the physical distance of reefs from floating plastics. A recent analysis of plastic debris in the ocean however showed that plastics carry lots of bacteria species, including pathogens, that can contribute to diseases in corals. These pathogens often prefer a low-oxygen, low-light environment, and thus flourish within plastic floats. Plastics sitting in the water column above corals serve as microclimates for these types of bacteria.

How Did This Happen?

Plastics made from fossil fuels have only been around for a century. Following WWII, the production and development of thousands of new plastic products exploded, transforming the industrial world to the point that life without plastics would be unrecognizable today. Plastics revolutionized medicine with life-saving devices, allowed space travel, lightened cars and jets, reducing fuel consumption and emissions, and saved lives with helmets, incubators, and equipment for safe drinking water.

However, the conveniences that plastics provide have resulted in a throw-away mentality that exposes the material’s dark side: single-use plastics now account for 40% of all plastic manufactured each year. While many of these items, such as plastic bags and food wrappers, have a short lifespan, they can last hundreds of years in the environment.

Researching The Connection Between Plastic And Coral Disease

A team of American and Australian scientists researched whether plastic debris in the ocean had an impact on coral reefs. The method they followed was to examine the health of more than 124 000 corals in more than 150 reefs in 8 regions of the Pacific Ocean. Their objective was to identify characteristics of diseases on coral tissues and link them to the presence or absence of oceanic plastic, as well as the mechanics of how plastic pollution affects reefs.

The scientists published their results in the journal Science, and it was discovered that the risk of disease was up to 22 times greater in corals that were exposed to plastic than in preserved reefs, meaning that the likelihood of finding a diseased coral rose from 4% to 89%. It was found that the most common coral diseases – skeletal eroding band, white syndromes, black band, growth anomalies, brown band and atramentous necrosis – are more prevalent on reefs polluted with plastics. However, not all coral species were affected in the same way by the presence of plastic. The more complex and branched corals, such as staghorns, were more likely to retain debris and become entangled, and these corals were thus more susceptible to disease. This is a big concern for coral reef ecologists, as these elaborate corals often provide nurseries for fish species.

How Does Plastic Cause Coral Disease?

Exactly how the corals become diseased from encountering plastic such as bags, fishing lines and water bottles must still be researched. The scientists do however have some hypotheses on how plastic is increasing the prevalence of coral disease. Plastic debris has a direct effect on the corals by physically damaging the coral tissue. Pathogens and bacteria clinging to the plastic can then easily infect the corals, and the corals expend all their energy on its immune response as it attempts to repair the physical damage. This is all the more worrying, as another study published in ScienceDirect suggests that corals are voluntarily ingesting plastic, as they are attracted by its taste, possibly due to the chemical additives present in plastics. The pathogens cause diseases such as black band disease – a thick black band that moves across the coral, causing irreparable tissue damage. Plastic objects can also smother the coral by covering the coral’s surface and blocking oxygen and sunlight, further promoting an environment that allows bacteria to thrive.

Coral reefs are the incubators of biodiversity in the ocean, and plastic is only one of the latest in a long list of human-linked stressors that are negatively impacting coral reefs. Coral reefs are already under enormous strain due to climate change and rising ocean temperatures, which results in coral bleaching and coral mortality, as well as overfishing and unsustainable agriculture practices. The increased stresses placed on corals will increase the susceptibility of corals to diseases. Researchers have discovered that coral species that have proven to be the hardiest in the face of other stressors and threats are just as susceptible to plastic-caused diseases as less-hardy species. Large boulder-shaped corals are often able to survive bleaching events, however these same corals were nearly twice as likely to fall ill when exposed to plastic pollution.

It Is Going To Get Worse Before It Gets Better?

Researchers have estimated that based on current trends, plastic pollution in the ocean is going to continue to rise. Out of the top 10 worst plastic polluting countries in the world, nine are located in the Asia-Pacific region. Unfortunately, more than 55% of the world’s coral reefs are also found in the Asia-Pacific region.

Although many countries are making a move to ban all single-use plastics and place a surcharge on plastic goods, it is argued by environmental groups that more can be done by governments and large corporations to combat oceanic plastics. Although individual households can recycle, pressure should be placed on corporations and governments to take more responsibility. Plastics must be taken into account when planning reef management and conservation, and countries must reinvent their waste management practices to prevent plastic from entering the ocean. Of course, this does not address the masses of plastic already floating in the ocean, where it is degrading into microscopic particles. Although reducing plastic use and concurrent pollution will not be enough to save reefs, it will ease some of the pressure that reefs face from other threats.