Are blue crabs mixing a side of plastics into their diets?

University of Delaware Associate Professor Jonathan Cohen examines a tray of tiny plastic pieces, called microplastics, at the University of Delaware Lewes campus. He’s part of a small team researching the impact of this type of pollution in the Delaware Bay.
Photo by Jenna Miller/Delaware News Journal

[This article was originally published by The Delaware News Journal]

Picking the steamy, sweet meat from blue crabs is a hallmark of summers spent on Delmarva, when the spicy flavors of Old Bay and butter mingles with the scent of saltwater and the sound of seagulls.

But what if those crabs spread across a paper-lined table were seasoned with something more unnatural, something unseen? Could it be possible that tiny pieces of plastic found in waters along the Delaware coast are making their way into those crabs’ diets?

That’s exactly what Delaware marine scientists aim to find out.

It’s not likely that the succulent white meat plucked out of a Delaware or Maryland blue crab’s cavities is more plastic than meat. Scientists do have reason to believe, though, that the tiniest forms of plastics may have become an unnatural part of crabs’ diets.

Jonathan Cohen, research lead and associate professor of marine biosciences at the University of Delaware, colleague Tobias Kukulka and scientists with the Delaware Department of Natural Resources are trying to figure out how the region’s blue crab population interacts with plastics, and whether adult crabs destined for steam pots could have an extra polyethylene-seasoning.

“We’re seeing evidence of a potential problem elsewhere and now we’re just trying to back fill all the information to see if that problem is one in our backyards,” Cohen said. 

Copps Seafood near Millsboro has been in business for nearly 50 years, but the idea of microplastics impacting the blue crabs they depend on is a new concept to the business’s matriarch Kay Copp.

“That might be because I don’t get to read too much in the summer,” the 78-year-old joked. 

Copps, which is now run by Kay’s son, goes through about 15 bushels of crabs per day. A bushel can fit up to six dozen No. 1 crabs, she said. Some years are better than others, depending on the weather and the size of crabs available.

“You see poor fish with plastic around them, and all kinds of stuff, it’s sad,” she said. “How are you going to stop plastic? It needs to be [stopped] … Bottles of water are nice, but we never used to have them years and years ago and we made out fine.”

In recent years, plastics pollution has been pushed into a national spotlight. Straw and bag bans are sweeping the country, and international voices like Greta Thunberg, Time magazine’s 2019 Person of the Year, are waging a war against single-use plastics that can end up in local streams and rivers on their way out to sea.

It’s well known that large pieces of plastic pose a problem in the marine environment. They’ve accumulated into the Great Pacific Garbage Patch, a collection of plastics and trash twice the size of Texas floating in the Pacific Ocean.

When mistaken for food, discarded plastics can choke and strangle beloved animals like sea turtles and seals. Other species, including whales and dolphins, have been found dead in recent years with bellies full of plastic.

The plastic pollution that doesn’t get eaten eventually breaks down in the environment into little fragments known as microplastics.

Whether plastics break down from other pollution or come from wastewater treatment plants, microplastics can end up in the environments and stomachs of much smaller marine organisms at the very base of the food chain. Whether they ultimately end up on people’s plates, though, remains unseen.

In late November, scientists published a paper that found researchers had seriously underestimated how many of those microplastics have made it to sea. The reality is probably five to seven times worse than previous estimates, with millions more teeny tiny microplastics floating in the sea, a recent study found.

In the Delaware River watershed, our understanding of microplastics pollution is just starting to take shape. 

What are microplastics?

Microplastics are tiny pieces of plastic, smaller than 5 millimeters, which is about the size of a pencil eraser. There are three main categories of microplastics: fragments, fibers or filaments, and beads.

University of Delaware Associate Professor Jonathan Cohen and a small team of graduate students research microplastics in the Delaware Bay, separating out tiny plastic fragments from bits of wood or metal.
Photo by Jenna Miller/Delaware News Journal

Fragments are pieces of plastic that started out as something larger, like a plastic bottle, bag, toy or container. Imagine crunching up a potato chip. If that chip were made of plastic, the crumbs in your hand would be microplastics.

Fibers or filaments are like tiny threads that come from clothing, rope or fishing line. Imagine a well-used microfiber fleece sweater. The little hairs that stick out of it, if they were removed one by one, would be microplastic fibers.

Beads are small, spherical plastics designed at that size, to be used in products like exfoliating face washes and toothpastes.

Microplastics can get into the environment as larger plastic litter breaks down and from wastewater treatment plants that discharge into bodies of water. They can be found in the water, sand and sediment and in marine animals’ digestive systems in aquatic environments. Microplastics have also been detected in the air we breathe, the food we eat and even the pristine snow of the Arctic.

From plankton to plastics

For decades, Cohen had studied plankton, the coast’s tiniest aquatic organisms, and noticed an alarming trend. 

In addition to the microscopic critters like copepods that he was studying, his samples were also turning up lots of tiny pieces of plastic.

By 2016, he enlisted marine science students to help launch the first comprehensive look at microplastics in the Delaware Bay. They began by taking water samples to find out how many microplastics – and what types of plastic – there were out there.

“No matter where we sampled in the bay, there was plastic,” said UD graduate student Anna Internicola. “I think it was eye-opening to know that it’s everywhere.”

This graphic by Blue Raster below shows the sampling sites of three of the research projects looking at microplastics in the Delaware River Basin. Sampling techniques and methodologies may vary between projects, and additional projects in the works may not be included.

In November, Cohen and his team published a paper on their findings that identified hot spots of microplastics in the Delaware Bay – like their sampling site near the Delaware Memorial Bridge.

But they also warned that the way water moves in an estuary like the Delaware Bay makes it difficult for researchers to see the full picture of microplastics without lots and lots of samples from many different locations and conditions.

Cohen said they found what would be akin to two to four pieces of plastic in a bathtub full of water in some of those hot spots. But that modeling shows that the influence of tides, currents and mixing of salt and fresh water could change that number.

“In the Delaware Bay and Chesapeake Bay, there’s a lot of unknowns about microplastics, and we’re filling in a lot of gaps in relatively short order,” Cohen said over the summer.

They also studied, with support from Delaware Sea Grant, what type of plastics they were finding. That is a key to figuring out where the pollution came from, Cohen said. The top two are polyethylene and polypropylene.

The takeaway? Microplastics can be found in most every water sample taken from the Delaware Bay, and how the water moves can drastically change where and when they show up.

This graphic by Blue Raster maps concentrations of microplastics in samples collected by University of Delaware researchers in April 2017, according to their data.

The question remains as to where they’re coming from and what risks they might pose.

Researchers plan to continue asking questions like that for local waterways. They’ll also take their studies to the Outer Continental Shelf and other places that blue crabs roam on their three-week journey from larvae to pincher-wielding adults.

That includes studying, in the laboratory, how crabs interact with microscopic plastic throughout their life stages. That also means analyzing tiny crab larvae poops to learn how many – and if any – microplastics they might be eating, and if that diet additive interferes with their ability to grow big and strong enough to end up on someone’s picnic table.

Starting in late spring or early summer, there will be buckets upon buckets of egg-laden blue crabs sprawled across the Lewes campus laboratory floor. Cohen and his research assistants,  , with support from NOAA’s Marine Debris program, will hatch and study local crabs for how they might interact with plastics to learn more about the biological effects of plastic pollution along the Delaware ocean coast and bay.

“It’s definitely in our backyards,” Cohen said. “Then the question becomes what sort of biological effects might there be?”

It has taken years just to set this baseline of microplastics pollution in the Delaware Bay.

In other parts of the estuary, that work is just getting started.

This story has been produced as part of “From the Source: Stories of the Delaware River,” a year-long collaborative reporting project produced with support from the National Geographic Society, the Lenfest Institute for Journalism, and the William Penn Foundation. Editorial content is created independently of the project’s donors.

Do you have an environmental story tip? Contact reporter Maddy Lauria at (302) 345-0608, or on Twitter @MaddyinMilford.

Leave a Reply