The latest threat to corals? Unsurprisingly it’s plastic

A new study has found that not only are corals filling up with plastic, but they may even be doing it on purpose. It is the latest in a long line of human driven factors that are pushing corals to the very brink.

The northern star coral has been found to have an alarming amount of micro-plastic hidden away in its polyps

There is just no escaping it. From the Arctic to Antarctica, on the surface to the seafloor and inside every type of marine organism. Plastic is everywhere in the oceans and no one seems to be safe from it. The latest victims are a group already suffering from our effects on the oceans, corals. A shocking discovery from researchers at Boston University has revealed that 100% of sampled corals contain micro-plastic particles. But it doesn’t end there. The team have also shown that for unknown reasons the corals are actively ingesting plastic over other food sources. Although this study is not the first to find plastic in corals it is quite possibly the most alarming. The findings also highlight yet another dangerous new threat to coral species who are already suffering from climate change, ocean acidification and a host of other human caused issues. The race is now on to research the effects plastic can have on corals before the problem inevitably gets worse.

A preference for plastic

The coral in question here is the northern star coral, Astrangia poculata, a stony coral native to the north Atlantic and Caribbean regions. News of its plastic consumption comes from a new study by a team from Boston University led by Randi Rotjan. Their work was split into 2 different experiments that each produced very alarming results. Firstly four colonies of northern star corals were collected from off the coast of Rhode Island and brought back to the lab for analysis. That analysis showed that 100% of the coral polyps contained micro-plastic particles, and not just one or two pieces. On average each individual polyp contained 112 plastic pieces which was significantly greater than expected. This was quite alarming considering as filter feeders you would expect the levels of micro-plastic to be consistent with that of the water they come from.

Each individual polyp of the northern star coral had an average of 112 plastic pieces inside them

The researchers then changed tactics and looked at just how the corals were ingesting so much plastic. They gave the corals a choice of micro-plastic particles and similarly sized brine shrimp eggs, a natural food source for the corals. Surprisingly the corals chose to eat the plastic over the shrimp eggs for no apparent reason. After realising this the team then coated the plastic particles in E.coli bacteria to see if the pathogen could be transmitted to the host via the plastic. The answer was unfortunately yes. Rotjan describes the particles as “a little plastic raft where all these bacteria can hitch a ride”. Meaning plastics could increase the chances of another big killer of corals, diseases.

Another nail in the coffin?

So just how dangerous is this new problem for corals? On its own it may not actually be that much of an issue. After all there is no evidence that plastic alone can significantly damage or kill the corals they pollute. However corals are already under a tremendous amount of stress from human caused factors such as climate change, ocean acidification, eco-tourism, overfishing and chemical dumping. All of which contribute to the biggest threat to corals known as bleaching. This is where due to severe stress caused by drastic changes in their environment the corals expel their endosymbiotic phytoplankton, known as zooxanthellae, causing their tissue to turn white and unless their plankton partners return soon afterwards death.

Micro-plastics are just the latest in a long line of threats facing corals

This makes micro-plastics and the risk of disease a major issue for corals as it adds to the list of problems that can cause them to bleach. But on top of that it could also be the worse yet as plastics can compromise the immune system of corals which lowers their bleaching threshold. This means that it could take less stress or change to cause bleaching events which would make factors like rising ocean temperatures and acidification much more deadly to corals. However it is still not really understood how all these factors are interconnected and therefore much more research into the effects of plastics on corals is needed. Rotjan believes that “this study opens the door to those ‘now what’ questions” and encourages others to help her in studying the subject.

Microscopic mayhem

Unfortunately corals are not alone. A large quantity of research in the last few years has pointed out that micro-plastics are affecting almost all marine species in one way or another. The plastic particles, less than 5mm in diameter, are abundant across the marine food web and now even effecting primary producers like corals. We are constantly discovering new health problems associated with the tiny troublemakers, not just for marine animals but also for ourselves when we consume them via seafood. It is now believed that the average human consumes as much as a credit cards worth of plastic a week. Unfortunately the problem is only going to get worse as more micro-plastics enter the oceans and larger plastics break down into smaller and smaller pieces. It is unknown if the micro-plastic problem is even solvable at this point or has already become an issue that will plague our oceans for the rest of their existence. But as we become more aware of just how important this issue is we must continue to learn as much as we can in order to tackle it.

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