.Microplastics Found Inside Monterey Bay Sealife

Scientists from UCSC and Monterey Bay National Marine Sanctuary discuss the microplastics problem and what people can do about it

The recent storm littered local beaches with driftwood and trash. Plastic pieces of all sizes tumbled in the surf and settled into the rubble. But the storm didn’t bring the plastic—it just highlighted its existence. 

Some of the particles will get picked up by volunteers and mindful beachgoers. But lots of it will wash back out to sea and break down into smaller and smaller pieces. 

When it degrades to less than five millimeters long—about the size of a pencil eraser—it’s microplastic. In a recent study, scientists found microplastics inside an alarming number of seabirds and anchovies from Monterey Bay. The research, published in the scientific journal Environmental Pollution, also suggested that some particles could disrupt hormones, potentially spelling trouble for wildlife populations.

Piecing it Together

Sami Michishita led the research as a graduate student at UCSC. She knew she wanted to study seabirds and plastics before she began her degree, and the Monterey Bay proved an excellent place to do it.

She chose to examine common murres—sea birds that spend most of their time on the open ocean and feed on small fish—and anchovies.

“Common murres are a resident bird species, so they’re a good indicator of what’s going on in the Monterey Bay,” says Myra Finkelstein, Michishita’s advisor and an adjunct professor in the microbiology and environmental toxicology department at UCSC. “They’re an ecologically important species. And so are anchovies.”

Common murres eat anchovies, which was a vital link for the research. Some toxins transfer from prey to predators in a process called trophic transfer. These toxins can then accumulate in greater concentrations in animals that are higher on the food web. Ecologists call this sequence of events biomagnification. 

Scientists are still trying to determine whether microplastics biomagnify like this in food webs, so Michishita compared microplastics collected from seawater, anchovies and murres. She found similar types of microparticles in all three. 

“We can’t 100 percent say that the murres had plastic in their stomachs because they ate anchovies that had plastic in their stomachs,” says Michishita. “But we found a lot of similar types of plastics—polyesters—in both digestive tracts.”

The scientists received anchovies from a sustainable Community Supported Fishery group based in Santa Cruz. The California Department of Fish and Wildlife Seabird Health Program provided samples from common murres.

The team found human-sourced microparticles in the digestive tracts of 58% of the anchovies they sampled and 100% of the murres. Of that, over 57% were confirmed as plastic using spectroscopy. 

“The majority of work to see how much plastic is in seabirds has looked at the macro plastic—the bigger pieces that you can see with your naked eye—and in those studies, less than 10 percent of murres were found to have plastic,” says Finkelstein. “But the fact that now we looked at these smaller little pieces, where we have to use a microscope, and found 100 percent of them had these microparticles, to me, was really alarming. And also, unfortunately, probably illustrates that these little microparticles are everywhere.”

A Pervasive Problem

That microplastics are everywhere is no exaggeration. A 2019 study conducted by the Monterey Bay Aquarium Research Institute found microplastics in the water of Monterey Canyon below 1,000 meters, roughly 3,300 feet deep. 

Monterey Bay National Marine Sanctuary (MBNMS) scientists also study microplastics with a five-year monitoring plan.

“We know it’s fairly ubiquitous in the marine environment; we just don’t know what the long-term implications are,” says Chad King, a federal ecologist at MBNMS. “We don’t know the long-term health effects on not only human health but the marine ecosystem itself.”

To learn more about the issue in Monterey Bay, the sanctuary is developing a pilot program for monitoring microplastics in beach sand.

“We need to start answering the questions of ‘where’s it coming from,’ and ‘what can we do to reduce the amount,’” says King. 

For example, if most of the microplastics are microfibers, that might suggest local laundry machines as a source. But the researchers don’t expect determining sources or solutions to be simple. 

“At this point, it’s coming from everywhere, and we can’t just find a single source. It’s such a global problem,” says Lisa Uttal, the education and outreach specialist for MBNMS.

Still, the sanctuary is working to spread awareness among community members. A water quality team works with the agricultural industry to encourage best practices surrounding the plastic sheeting used in fields, for example. 

“It is a high priority of the sanctuary to address this issue,” says King. “And we have a long-term action plan, and we’ve committed a lot of resources and staff time to address this issue.”

Hormone Havoc

One of the reasons scientists are so committed to studying microplastics is the detrimental health effects they could have on people and animals.

Some chemicals used in plastics have similar structures to hormones and can bind to hormone receptors in the body. These are known as endocrine disruptors, and one of the most infamous examples is Bisphenol A, commonly called BPA.

Endocrine disruptors can wreak havoc on the body’s development, reproductive system and immune system. They’ve been linked to diabetes, cardiovascular disease, early puberty, fertility irregularities and brain development disruptions, among other effects.

These consequences are well established, but few studies have involved microplastics. And few microplastics studies involve testing their ability to disrupt hormones.

“A lot of studies stop at just looking at how much plastic is present,” says Michishita. “We took it a step further by actually leaching those plastics to get additive chemicals from that plastic and seeing if they could activate estrogen receptors.”

They could. 

The scientists worked with the San Diego Zoo Wildlife Alliance and found that about a fourth of the murres had microparticles inside their guts that could activate human estrogen receptors.

“It could mean that in addition to the microplastic inside, they may be causing some sort of harm in terms of inflammation in the digestive system and localized effects. They might also be leaching toxic chemicals that could be impacting the murres’ ability to reproduce or shorten their lifespan,” says Finkelstein.

Her lab will continue investigating the biological impacts in collaboration with the San Diego Zoo Wildlife Alliance.

“This is a really big problem of our generation,” says Finkelstein. “Plastic production is exponentially increasing. And on the other side, this plastic pollution will also keep increasing exponentially. And we need to figure out as a society what we’re going to do about this unless we want to live in a plastic-polluted world.”

Although the problem can feel overwhelming, Finkelstein encourages action. 

“I think people on an individual basis can do their part in terms of trying to minimize their own plastic use—especially single-use plastics,” she says. “But I think more importantly, support politicians that care about this issue and might make these more difficult changes that we have to do and invest money in research to try to think of alternatives—I believe we can fix this issue; we just have to prioritize it.”


  1. Thank you for your commitment to this problem! Please let the public know definite things we can do to lessen our contributions to the issue.

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