by Erin Minor

Plastic pollution in our ocean is growing daily. Scientists estimate 12 million U.S. tons of plastic enter the ocean every year, and it makes up 80% of all marine debris.

How can we hope to keep track of this vast amount of plastic, or detect any useful patterns to help get it under control? One way is to collect plastic samples using animals. Marine animals ingest plastic that has broken off from plastic trash and ends up in the ocean. Scientists can then measure how much of this plastic has accumulated in the bodies of these animals. Scientists have used this method for decades.

“Sampling microplastics can be challenging and expensive,” said Martin Thiel, a marine biologist at the Smithsonian Environmental Research Center (SERC). Thiel co-authored an article in Environmental Science Advances reviewing how scientists around the world use animals to study ocean plastic. Using animals, he said, allows scientists to more efficiently collect data. “It can tell us not only how many plastics are in the environment, but how the organisms are affected by this type of pollution.”

Here are some of the most popular animals scientists use for plastic pollution research.

Feathered friends: Northern Fulmar

The northern fulmar is a seabird found in the North Atlantic and North Pacific. These birds spend large parts of the year out on the open ocean, scavenging for meals along the water’s surface. They often mistake small pieces of plastic for organisms living on the surface and regularly ingest them. The birds cannot digest the plastic, which then accumulates in their stomachs over their lifetimes. This makes fulmars good candidates for this type of research because they allow scientists to collect samples from the open ocean where it is more difficult to test the water for plastics. In the Netherlands, researchers have been monitoring their plastic ingestion in the North Sea for the past 40 years.

This research is a prime example of how scientists hope to standardize this type of data collection around the world. The 40-year history of this study means the data can be compared over time, telling us how plastic pollution has changed. Scientists also hope to be able to compare datasets over space. The northern fulmar study has been mirrored on the other side of the North Atlantic, in Canada.

“The results are still coming in, but there are the first inklings of declining plastic ingestion in these fulmars on the Canadian coast, which is reflected by recent data from the North Sea,” said Matthew Savoca, a marine ecologist at Stanford and lead author of the paper. “It remains to be seen if these trends hold, but beginning to see trends like these emerge shows the power and promise of monitoring plastics in animals in standardized ways across oceans.”

Wide-ranging reptiles: Loggerhead Sea Turtle

Another characteristic scientists look for is a wide habitat range. If a species lives all over the world, scientists can compare data from the same species in many places. Loggerhead turtles are an excellent example, as they can survive in temperate and subtropical regions of the Atlantic, Pacific and Indian Oceans. They also like different foods than the birds do, enabling scientists to track different kinds of plastics. 

“Sea turtles tend to prefer soft plastic and rubber items, compared to the small hard fragments that fulmars consume,” Savoca said.

However, each type of animal comes with its own challenges when it comes to collecting data.  Large animals like the northern fulmar or loggerhead turtle require opportunistic sampling—researchers must wait for them to die of natural causes and then wash up on shore before they can collect samples.

Microplastic Monitors: Bivalves

Bivalves like mussels, clams and oysters don’t require researchers to wait for them to wash up on a beach. Scientists can sample them on a regular basis. Bivalves are also filter feeders, meaning they filter water through their tissues and absorb nutrients. This makes them excellent candidates for evaluating microplastic pollution.

Additionally, they stay in the same location, helping researchers get a clearer image of a narrower area. While the wide ranges of large animals like the fulmar and loggerhead can be helpful for sampling remote areas that are difficult to access, it also means that researchers can’t determine exactly where the plastic is—because they don’t know where the animal first picked up the plastic. Stationary shellfish don’t have that problem.

Monitoring bivalves is not without drawbacks, however. The very small microplastics that get absorbed by these filter feeders are harder to measure, requiring more specialized equipment that not all researchers have access to. This highlights another problem scientists face in their mission to standardize data collection around the world: The kind of data that a lab can collect depends on the resources and technology available to them.

Wanted: Deep Sea Species

One area that still needs monitoring is the sea floor. As of right now, there are no projects that use organisms for long-term tracking of plastics in the deep sea. But if we want to understand the role that plastic pollution plays in deep-sea ecosystems, we need to find a consistent method to monitor its prevalence.

“There are huge portions of the ocean that we have little to no information about that are in dire need of baseline data and monitoring,” Savoca said. “We are in the process of figuring out which species would serve to best monitor these habitats.”

Preliminary studies have considered using deep-sea animals like sea spiders, sea cucumbers or jellyfish, among others. But scientists are still on the hunt for an accessible species that will regularly accumulate plastic pollution from the ecosystem.

Thiel says that the most important part of continuing this research lies in having that information in the future.

“What these efforts are good for is not to decide whether or not we need to take action now—we know that we do—but so we can see in the future whether the measures we’re implementing are working or not.”

A full copy of the article, “Monitoring plastic pollution using bioindicators: a global review and recommendations for marine environments,” is available at https://doi.org/10.1039/d4va00174e

More Plastic Pollution Articles:

Do We Live in the Plasticene? 12 Words to Know for the Age of Plastics

Ocean Plastic Is Creating New Communities of Life on the High Seas

These Creatures Crossed the Pacific on Plastic Tsunami Debris. Now, a New Struggle for Survival