Stephanie Monmoine

 

A Series of Duke Studies Indicates Marine Organisms Like the Taste of Plastic

 

It’s nothing new to scientists that corals eat microplastics mistaken for food, but a recent study at Duke University is the first to suggest that they might have an actual preference for certain types of plastic based on taste alone.

 

Corals rely on chemoreception to find food, meaning a feeding response is stimulated by certain chemical compounds found on prey. Based on the findings of the study, this means some chemicals found in the plastics may be triggering this feeding response.

 

Austin Allen, a former doctoral student in Duke’s marine science and conservation department, made the discovery while trying to prove the exact opposite.

 

“It’s the first study indicating that taste may be a major factor of ingestions,” said Allen.

 

Microplastics are small pieces of weathered plastic less than 5 millimeters in diameter. These small plastic particles started accumulating in the oceans for over four decades ago when plastic started gaining popularity. The particles are dangerous for sea animals to consume, especially foraging fish such as anchovies.

 

The plastics are mostly indigestible, so they remain in the organisms’ stomachs, leaching chemicals into their bodies and the surrounding environment. Plastic consumption can be particularly harmful because it takes up space normally filled by food according to the study, giving organisms a false sense of fullness.

 

“About eight percent of the plastic that coral polyps in our study ingested was still stuck in their guts after 24 hours,” said Allen.  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Allen and his co-author, Alex Seymour, intended to prove that corals had a preference for microplastics covered in biofilm, a bacterial cover that coats almost everything in the ocean. Instead, they found that corals preferred the taste of some of the chemicals in the plastic to the naturally produced biofilm that contains nutrients that could be helpful to them.

 

“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 Allen.  

 

Allen and Seymour came across a paper from 2015 showing the first instance of corals ingesting microplastics off the coast of Australia. The study only used “clean” microplastics, meaning they weren’t covered in biofilm like they naturally would be in the ocean. This piqued Allen and Seymour’s curiosity as to what corals would prefer between “clean”  microplastics and ones naturally covered in biofilm.

 

Out of this curiosity stemmed their study attempting to determine whether corals will ingest a variety of plastic types, and if a microbial biofilm affects ingestion or retention rates of plastics, compared to plastics without a biofilm.

 

Allen and Seymour conducted their two-part study using corals off the North Carolina coast at Duke’s Marine Lab in Beaufort, North Carolina. What they call the first experiment was actually conducted after the second experiment, but it made more sense to reverse the order after knowing the results.

 

In their first experiment, they offered small amounts of eight different types of microplastics to the corals to see if the animals would prefer the smallest bits of plastic to similarly sized items like clean sand.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

In the second experiment, they put groups of coral into separate feeding chambers. Each group was offered the same amount of weathered plastics for a 30-minute period, but some groups got “clean” microplastics while others got weathered microplastics covered with a bacterial biofilm. This experiment suggested that the corals would eat both types of plastic, but preferred the clean type by a three-to-one margin.

 

This has immense implications for plastics manufacturing companies. If it’s proven that specific chemicals that they put in the plastic make them more appealing to marine organisms, it would be hard for them to avoid making a change.

The plastic retention rates observed in this study are related in part to the shape and form of the test plastic, which can influence the amount of time it remains in the organism, according to the study.

 

While Allen and Seymour have moved on from the study, Dan Rittschof continues the search at Duke in Durham, North Carolina. He and his team are using anemones and barnacles as models for this study because they are it is being conducted away from the coast. They are expanding on the study to discover which chemicals are leaching from the plastics, and from those, which chemicals the marine organisms are the most attracted to.

 

If they succeed in identifying the most problematic chemicals, Allen believes that “ we could manufacture plastic without those chemicals.”

While the study highlights the need for research into the impact of plastic pollution on corals, it also raises questions about why animals ingest plastics.

 

As more and more marine organisms at the base of the food web are shown to ingest microplastics, it is important to know whether they are targeting microplastics or just mistaking them for real food based on smell. If they are seeking out microplastics over real food, it’s important to know if chemoreceptor activation is the reason for ingestion.

 

The study not only has implications for many other species that use chemosensory cues to detect prey like corals, but also for humans as the plastic bioaccumulates along the food chain and the environment itself.

 

The plastic problem is only getting worse as the amount of solid waste generated annually in cities continues to rise and is expected to be 2.2 billion tons by the year 2025, according to the study.

 

“There’s more plastic than fish right now,” said Dr. Dan Rittschof, a professor and researcher at Duke who co-authored the original study with Allen and Seymour.

 

Dr. Rittschof was among the professors and researchers who continues variations of the study, along with Melissa Chernick, a research technician at Duke University. Chernick is using the aquatic model fish Japanese medaka to study the health effects of consuming the different types of plastic.

 

“We are looking at the environmental implications with some looks at human health,” said Chernick as she stood in front of thousands of tiny fish in what she calls the exposure room.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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The exposure room is where the breeding colonies of medaka reside, alongside rows of zebra fish that are part of a different study.

 

Empty tanks line the walls of the room, and there’s a constant humming from the filtration system. Cassandra Nieman, a Master’s student in environmental management, feeds the fish an orange liquid solution containing thousands of fresh brine shrimp through a syringe.

Fish of all ages are kept in the exposure room until they are ready to be exposed to the plastic. They are moved upstairs to Chernick’s lab to be fed concentrated pellets of different types of plastics.

 

The smallest plastic pellets ingested by the fish were made in Singapore by students in one of Duke’s study abroad programs.  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Small glass containers filled with different colored pellets of plastic line the shelves of the lab Chernick shares with a couple other researchers. Next to the containers are small test tubes coated in foil. The aluminum foil shields the tubes from light because the plastic is injected with a chemical to make it fluorescent so that it’s easy to identify where the plastic ends up in the fish.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Medaka were chosen for exactly this reason. Because the females are entirely transparent, it’s easier to identify the location of the plastic in the fish and how variations in location affect the fish.

 

“We can put them to sleep, look at them, then wake them back up,” said Chernick.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chernick is working to identify the detailed effects of the plastic on the fish’s health in the hopes of applying that knowledge to determine the larger scale effects on human health and the environment because those effects are currently unknown.

 

Dr. Dan Rittschof, co-author of the original study with Allen and Seymour and a professor and researcher at Duke in the Marine Science and Conservation division, is conducting another variation of the study. The study focuses primarily on the physiological effects of consuming plastics.

 

Dr. Rittschof is using barnacles and sea anemones as model organisms to look at the effects of plastic consumption on their reproductive abilities and hormone composition. He is also researching which of the chemicals leached from the plastics are the most toxic and the most attractive to the organisms.

 

If these studies can link certain types of chemicals in plastic that attract marine organisms to a greater overall impact on the environment and human health, it could push enough research to make real changes to the plastic industry.

 

Plastic’s ability to mimic the taste, smell, appearance and texture of food items will continue to have increasingly dire consequences for environmental and human health.