Corals Eat Plastic Because It Tastes Good! Could The Same Be True For Other Marine Animals?

You may have heard how hundreds of turtles die each year thanks to plastic pollution in the oceans. These poor creatures mistake floating pieces of plastic for food, thinking it's jellyfish or something, eat it and often die from complications like intestinal blockage. 

But this is a problem extending to other species as well. To give you an idea, it is estimated that approximately 100,000 turtles, dolphins, whales, seals and other marine animals die each each year by plastic litter!

Now, a new study by researchers at the Duke University on coral reefs suggests that visual cues might be only one reason why marine animals confuse plastic for food!

Coral reefs like marine animals also "enjoy" eating plastic, but unlike other marine animals (yes corals are animals too!) they have no eyes to mistake it for food. Is this accidental? Or maybe they just like the taste of it?

White fleck of plastic engulfed by a coral polyp (Credit: Alex Seymour, Duke University)

Well, it turns out that corals find plastic too good to resist:

 "Corals in our experiments ate all types of plastics but preferred unfouled microplastics by a threefold difference over microplastics covered in bacteria. This suggests the plastic itself contains something that makes it tasty." said Austin S. Allen, PhD student at Duke's Nicholas School of the Environment and first author of the study. [1]

What exactly makes plastic so delicious though still remains a mystery:

"When plastic comes from the factory, it has hundreds of chemical additives on it. Any one of these chemicals or a combination of them could be acting as a stimulant that makes plastic appealing to corals." said Alexander C. Seymour, a geographic information systems analyst at Duke's Marine Robotics and Remote Sensing Center and co-author of the study.

For this study, the researchers conducted two experiments, using corals collected from waters off the North Carolina coast. 

Experiment 1

In the first experiment the researchers offered eight different types of microplastics (small plastic pieces less than five millimeters in diameter) and some other similar sized items like clean sand to the corals:

"We found that the corals ate all of the plastic types we offered and mostly ignored sand." Allen said. [2]

This made clear that for some reason corals do find plastic tasty!

Experiment 2

In the second experiment the corals were put into two groups and were offered two kinds of plastic. 

One group received "clean" plastic while the other received plastic that was covered with a bacterial biofilm. This was done because a prevailing theory is that marine animals eat plastic items because they are often covered by additional organic compounds which makes them more appealing.

The results from the second experiment were quite surprising! Yes, both groups ate the plastic particles, however corals had a clear preference for "clean" plastic with no organic additives as they ate way, way more of it! 

" Contrary to our hypothesis, experiment two demonstrated that microbial fouling greatly reduced the amount of plastic ingested, though significant amounts of biofouled plastic were still consumed." excerpt from the paper. [2]

Comparison of the median total plastic consumed, plastic ingested and plastic retained (credit)

The Takeaway

Well, the obvious conclusion is that corals eat plastic because they love the way it tastes. The exact chemical compounds that make it so tasty are yet a mystery and definitely more research is needed in that area.

However, the study also raises some questions. Do other more complex animals like turtles and birds eat plastic because they mistake it for food? Or much like corals, they find plastic items tasty? And if the answer to this is yes, is there something we can do to make this plastic distasteful? 

"Ultimately, the hope is that if we can manufacture plastic so it unintentionally tastes good to these animals, we might also be able to manufacture it so it intentionally tastes bad. That could significantly help reduce the threat these microplastics pose." said Seymour.

References

1. Sciencedaily.com/releases/2017/10/171024141710.htm
2. Sciencedirect.com/science/article/pii/S0025326X17306112?via%3Dihub

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