Corals in crisis: The plastic pandemic surging through our seas

This was a piece I wrote recently for a module assignment at uni, it was the assignment that inspired me to start this blog so it seems only right to have it as my first post- my starting block.

Corals are one of the most fascinating global phenomena. Made up of tiny colonial organisms to create over 1,000 species that cluster together all over the world, they form the bursts of life that so many coastal communities depend on; our coral reefs. But the human race is putting these habitats at risk of extinction. Everyone knows our plastic waste threatens marine animals like turtles and seabirds, but the extent to which plastic is really polluting our planet is greater than many of us imagine. The fact of the matter is that corals are 20 times more likely to become infected with disease in the presence of marine litter. Furthermore, corals have been found to actively ingest small bits of plastic, potentially increasing their disease risk again. It’s time for us to clean up our mess. 

A 2018 study by Lamb et al., published in Science Journal, unveiled an alarming new threat to our most biodiverse ecosystems. Plastic as a transmitter of disease. The study looked at 159 reefs in the Asia-Pacific region from 2011 to 2014, sampling plastic greater than 5cm in length. They found a third of reefs in this region to have plastic debris. Indonesian reefs had an average of 25.6 plastic items per 100m2, whereas Australian reefs had an average of 0.4 per 100m2. It was this stark difference that first inspired Joleah Lamb, a marine disease ecologist who led the research team, to study the disease implications of plastic abundance on coral reefs. The study concluded that this presence of plastic increased the likelihood of disease from 4% to 89%- a factor of 20! These are the reasons why. 

Plastics make corals 20 times more likely to become infected with disease.

Humans put 11 billion tonnes of plastic in the ocean every year. This is largely due to poor waste management and ranges from cigarette butts, bottles and bags, to large fishing nets discarded at sea. A 2018 study by the US’ National Oceanic and Atmospheric Administration (NOAA) showed lifespans of these range from 1.5 to 600 years. When in the ocean, algae and micro-organisms attach to the plastic, creating what scientists call a biofilm. This biofilm includes pathogens which are viruses and bacteria. The problem is that attaching to such objects prolongs the lifespans of pathogens, allowing further distribution of a greater number of pathogens. Plastic marine litter acts like a city transport system; picking up and carrying pathogens through our seas, ready to infect living things. 

As plastic debris comes into contact with corals it passes pathogens into the coral tissue. Infection via plastic can happen directly by causing physical injury to the coral tissue and the direct introduction of foreign pathogens, like cutting yourself with a blunt, dirty knife. Infection can also occur indirectly by infecting organisms that the coral eats or relies on for its’ survival. Lamb and her research team found 3 diseases, in particular, to be associated with plastic contact. These 3 included white syndromes, black band disease and skeletal eroding band disease which, in particular, has been shown to accompany plastic inflicted wounds. They concluded that plastic polluted reefs face different disease threats to plastic- free reefs where these diseases were much less common. 

In addition to this ground-breaking study, it has been discovered that the corals’ problem with plastic extends beyond plastic debris to microplastics, too. A Microplastic includes any piece of plastic below 5mm which is often formed from the breakdown of larger plastics. Plastics are not fully broken down and recycled in the same way as dead plants or animals; the pieces of plastic just get smaller. This means that when an animal is predated upon by another, rather than being broken down, the plastic is moved through the food chain. The plastic builds up in the stomachs of animals, making plastics a recognised threat to marine life. The accumulation of plastics in the body continues all the way up the food chain… to humans. 

Research is emerging to suggest that corals will remove and ingest microplastics from the water column. A 2020 study by Corona et al. published in Frontiers in Marine Science found that mushroom corals were prone to ingest and retain plastics, particularly if they were covered in a biofilm. This is likely because the biofilm tricks corals into thinking the plastic is organic food. The consumption of micro-plastics is a potential cause for concern for scientists. If micro-plastics have a biofilm, that suggests they are harbouring diseases. If these are being ingested by corals, corals are putting themselves at greater risk of disease and will potentially hamper their own food consumption. However, whilst this link between micro- plastics and disease is likely, it is not yet confirmed, however the potential link makes our plastic issue all the more concerning. 

Worse still, the study by Lamb et al. established that complex types of coral, such as ‘branching’ forms, are 8 times more likely to be affected by debris than ‘massive’ forms of coral, which are often flatter. However, when in contact with plastic, massive corals have a 98% chance of being infected with one of the diseases associated with plastic, suggesting they have fewer immune defences. Nevertheless, complex corals are disproportionately affected, posing a problem for the entire ecosystem. Coral ecosystems rely on the complexity of the reef structure to create enough habitats for all the animals that live there. When reef complexity is reduced, there are fewer habitats available and the diversity of animals that live there diminishes. This is comparable to habitat loss for orangutans, tigers and rhinos from the deforestation that currently devastates our planet. Habitat loss on coral reefs has been shown to reduce fishery productivity by a factor of 3, having detrimental effects on the communities and industries that rely on them. 

The loss of coral reef complexity will significantly reduce biodiversity in one of the most important habitats on earth.

Many of the communities most reliant on coral reefs are part of the poorest countries in the world. Such countries also have disproportionately more plastic on their reefs, putting reefs in these regions at greater risk. Lamb’s study noted that Indonesian reefs had the greatest amount of litter per 100m2. Australia, on the other hand, the most developed of the countries sampled, had the lowest. Unsurprisingly, the reason behind this is the lack of resources for developing countries to create effective waste management, paired with the fact that waste from the western world is often shipped to these areas. Without intervention, such as targeted improved waste management, projections of reef plastic get significantly worse for developing countries, almost doubling in the next 5 years for countries such as Indonesia. To put this into perspective, plastic on Australian reefs is projected to increase only 1%. When all of this is taken into consideration with the high levels of fishing taking place in our seas, it becomes apparent that having more plastic in our oceans than fish by 2050, is a very real possibility. 

It’s clear that corals are at increasing risk of disease from plastic waste, a threat that, for decades, has gone somewhat unnoticed. Though the future of reefs may appear bleak, the problem is resolvable. Initiatives to reduce ocean plastic are already cropping up. For example, 4Ocean, a global plastic clean-up company, have cleaned up 11 million pounds of plastic from coastal regions to date. Similarly, the Ocean Clean-up, another plastic removal company focusing on new technologies to do so, aim to remove 90% of marine plastic pollution by both tackling plastic manufacturing and removing plastic from the ocean. The reality is, however, that with our continued dependence on plastics, the problem is not going to disappear.

It is our job to live as sustainably and consciously as possible. Though recently in the media corporations, like Shell, have been putting environmental issues down to consumer demand, it is actually our responsibility to challenge the system. We must put pressure on manufacturing companies to find and fund alternatives to plastic. Contact Coke-a-Cola. March against McDonalds. Knock at Nestle’s door. Do not let them think plastic is what we want. Corals are calling out for help; we must not ignore their cries.