Plastic waste in the ocean has been found to have a twentyfold increase of disease in corals; adding one more threat to the list of things that could potentially kill corals

Corals and coral reefs have having a pretty difficult time with coping with the alternations we human make to the environment. They have already shown to have a lot of problem coping with the increased temperature in the water, as well as problems with dealing with the ocean acidification. This has lead to a very high rate of coral bleaching all over the world, and many reefs that are located in warmer parts of the ocean is dying rapidly.

A picture from the coral reef Great Barrier Reef in Australia. Image by Wise Hok Wai Lum, posted with the Creative Commons Attribution-Share Alike 4.0 International license.

Now it seems that we must add yet another major threat to the list of problems for the coral, and a new paper has shown how dangerous plastic waste can be for the corals. Joleah Lamb was doing her doctoral thesis at James Cook University in Australia, and began to collect data about how plastic affected the corals, and the results were pretty insane. The final conclusion was that the likelihood of disease increased from 4 % for a single coral, to 89 % if the coral was tangled in plastic! This is about a twentyfold increase in the rate of disease, and this could prove to be a big problem in the long-term.

How the plastic affects the corals

So, what exactly happens to make the corals get more sick from having plastic wrapped around it? First let me clarify that we are talking about plastic that is tangled around the coral itself, not microplastic. The first issue it creates is light deprivation, a huge problem for these animals that depend on the symbiotic relationship with the cyanobacteria to provide them energy from photosynthesis. Another problem is toxin release by the corals themselves, which could potentially be very problematic if it get stuck inside the plastic that seals the coral. If it is completely sealed by a piece of plastic, the coral could even die from anoxia – meaning that it is suffocated because it lacks oxygen.

A coral reef close to the shore. By Wilson44691 at English Wikipedia [Public domain], via Wikimedia Commons.

All these problems can be disastrous for the corals who get tangled in plastic, but we haven’t even looked at the biggest issue – how the plastic waste is a perfect place for bacteria to grow, including bacteria that causes disease in the corals!

What happens is that plastic items such as shopping bags, bottle caps or soda bottles end up in the ocean. They can be here for several years, and during this time many different species of bacteria will colonize the item, making it a unique cocktail of different microorganisms. At this point the plastic might lie still for a long time, but it might also be swept away by a strong current or even a storm, and end up in a completely new place. Now this is where the problems come in. If these plastic items end up being transported and get caught in on a coral, the bacteria that have been living peacefully on the plastic item could be causing disease for the coral.

As mentioned above, the disease rate increased from only being 4 % for corals without any plastic entanglement, up to 89 % for those who has some type of plastic caught onto it!

The study estimates that there are as much as 11.1 billion different plastic items that have been tangled in with corals, and fear that this number might increase by as much as 40 % in the next seven years. During the study the researchers examined 125,000 reef building corals spread across 159 coral reefs in Indonesia, Australia, Myanmar and Thailand, and found plastic pieces in all size and shapes attached to the corals.

By Toby Hudson. CC BY-SA 3.0, via Wikimedia Commons.

Corals are very bad at handling disease

It might not sound too bad that the corals get infected by disease, but these organisms are not very good at handling the disease. Once a part of the coral has become infected, the chance of the entire coral dying is pretty high. Corals don’t really have a good immune system at all, so infections could prove to be very problematic for individuals that get affected by a disease-causing bacteria.

Plastic is a problem for other species as well

There a huge amounts of plastic released into the ocean every single day, and this is not only dangerous for the corals. Most marine mammals as well as a lot of fish can also be directly affected by the plastic pieces that end up being consumed. Sea birds and turtles also have a tendency to get stuck on plastic pieces, eventually leading them to drown, so most organisms in the ocean is negatively affected by the plastic in some way or another.

Want to learn more about corals? Make sure you didn’t miss any of these coral posts by @valth

• Some corals have the ability to emit fluorescent light!
• Corals and marine life seems to be thriving in the Bikini Atoll – the area where the US detonated 23 nuclear warheads during the Cold War!
• New research has found that certain parts of the Great Barrier Reef might offer opportunities for regeneration of most of the reef.

Thanks for reading

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