Study Finds Microplastics Pose Deadly Threat to Corals

Double whammy of plastic pollution and climate change endanger environmental and human health


A recent study found that northern star coral polyps routinely consumed microplastics, shown above in blue, over brine shrimp eggs, shown in yellow. (Rotjan Marine Ecology Lab at Boston University)

Coral reefs form the most biodiverse habitats in the ocean, and their health is essential to the survival of thousands of other marine species. Unfortunately, these vital underwater ecosystems are beginning to get a taste for plastic.

A Roger Williams University professor, working with a team of researchers, recently published a study that found corals will choose to eat plastic over natural food sources. Unsurprisingly, it’s not good for their health, as it can lead to illness and death from pathogenic microbes attached to microscopic plastics. It also adds to the stress already being applied to coral reefs worldwide, by acidifying and warming oceans, other pollution sources, development, and harmful fishing practices, such as dynamiting and bleaching to capture fish for aquariums.

The project grew from concern about the 6,350 million to 245,000 million metric tons of plastic in the world’s oceans, and the 4.8 million to 12.7 million metric tons of new plastic that enter annually.

Photographs and news reports have documented dead whales and seabirds found with stomachs full of plastic and of sea turtles suffocating from plastic straws clogging their nostrils. At least two-thirds of the world’s fish stocks are suffering from plastic ingestion, according to estimates, as much of the planet’s plastic pollution eventually makes its way into the ocean.

Roger Williams University associate professor of marine biology Koty Sharp recently told ecoRI News that plastic pollution presents a growing problem for both water- and land-based ecosystems.

“It’s a huge problem,” she said. “There’s really nowhere left on the planet that hasn’t been touched by plastics. We’re finding plastics in every organism we study.”

As much as plastic proliferation is a problem, Sharp is even more concerned about the impacts of a changing climate and how humans are using natural resources. She pointed to the manmade damage being done to Australia’s Great Barrier Reef as an example.

“We need to quickly and dramatically decrease our dependency on plastics and fossil fuels,” the microbiologist said. “This isn’t a problem a few people can fix.”

The study Sharp helped author was published recently in London’s science journal, Proceedings of the Royal Society B: Biological Sciences. It is the first of its kind to identify that corals inhabiting the East Coast of the United States are “consuming a staggering amount of microplastics,” which alters their feeding behavior and has the potential to deliver fatal pathogenic bacteria.

In their samples of northern star coral, collected off the coast of Jamestown, each coral polyp — about the size of a pin head — contained more than 100 particles of microplastics, according to the collaborative research team that included Sharp, Randi Rotjan, a research assistant professor of biology at Boston University, and colleagues from UMass Boston, Boston Children’s Hospital Division of Gastroenterology, Harvard Medical School, and the New England Aquarium.

Northern star coral can be found from Buzzards Bay to the Gulf of Mexico. Since it can be found along the coast of most East Coast urban areas, Sharp said it is a “powerful tool” in helping to understand microplastic pollution.

Although this study is the first to document microplastics in wild corals, previous research had found that this same coral species consumed plastic in a laboratory setting. A 2018 study found plastic pollution can promote microbial colonization by pathogens implicated in outbreaks of disease in the ocean.

The study co-authored by Rotjan and Sharp produced similar lab results. When the researchers conducted experiments of feeding microbeads to the corals in their labs, Sharp said they found that the coral would more often choose the fossil-fuel derivative when given the choice between plastic and food of similar sizes and shapes, such as brine shrimp eggs.

In fact, every single polyp, or mouth, that was given the choice ate almost twice as many microbeads as brine shrimp eggs. After the polyps had filled their stomachs with plastic junk food with no nutritional value, they stopped eating the shrimp eggs altogether.

The study showed that bacteria can “ride in” on the microbeads. In the case of the bacteria they used in the lab — the intestinal bacterium E. coli — the microplastic-delivered bacteria killed the polyps that ingested them and their neighboring polyps within weeks, even though the polyps spit the microbeads out after about 48 hours. The E. coli bacterium persisted inside their digestive cavity.

“Research has shown that there are virtually no marine habitats that are untouched by plastics,” said Sharp, noting that research abounds demonstrating that nearly all ocean water contains plastic pollution. “Because of that, it’s critical that we understand the impact of plastics pollution. Microplastics pollution is a matter of global health — ecosystem health and human health.”

She noted that the problem of plastic pollution extends far beyond what can be seen. Plastics never fully degrade in seawater, breaking down into smaller and smaller pieces. Invisible to the naked eye, microplastics remain suspended in the water column, and this is what corals and other filter-feeding animals take in to get their food, she said.

The researchers had anticipated they would find microplastics in wild corals, but they were shocked by the volume present in their samples, according to Sharp.

Another invisible factor is the presence of microbes that hitch rides with plastics floating in the ocean, winding up in the stomachs of many creatures. These plastic-riding microbes are growing in number and upending the delicate balance of ecosystems.

Sharp said the problem is being made worse by human-induced climate change, which is helping bacteria to proliferate. She noted that microplastics in the ocean are coated with microbes.

“We know that plastic particles provide an enriching habitat for bacteria that are not usually in very high numbers in seawater,” Sharp said. “The microbial aspect of microplastics pollution is largely underexplored — it’s critical that we learn more about how plastics can affect the dynamics, abundance, and transport of microbes through our ecosystems and food webs. Alteration of microbiomes in our marine ecosystems by human-induced threats like plastics pollution and climate change holds great potential to impact marine environments on a global scale.”

To help mitigate the problem of plastic pollution, Sharp offered some tips:

Minimize single-use plastics. Use reusable bags and mugs. Buy groceries in bulk. Decline a straw if you don’t need one.

Take a day to count. How many times in one day do you use single-use plastics. What is unnecessary and what can be eliminated or replaced with more sustainable products?

Demand lower-impact packaging and support products with sustainable packaging.

Support and advocate for legislation and lawmakers that promote innovative solutions and alternatives for sustainable packaging.

“Given that plastics pollution is an ongoing threat co-occurring with climate change, it’s critical that we do more research to understand how they impact marine ecosystems together,” Sharp said, “and take immediate actions to minimize human impacts on the world’s oceans.”


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  1. Corals, like shellfish, are known to consume many inert particles, including microplastic and silt. Like shellfish they reject the indigestible materials. All particles in the marine environment will become colonized with bacteria – this includes silt and microplastics. The vast majority of these bacteria are not pathogens and are simply digested. If you coat particles with pathogens and feed them to organisms you might predict illness.

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