Four OSU scientists connect and collaborate to try to understand the effect of microplastics in gray whales and the ocean’s food chain

 

By NANCY STEINBERG/Oregon State University

NEWPORT — The concept is so well-established that it’s almost cliché — the most important thing humans know about ecosystems is that everything in them is connected. Case in point: Gray whales in Oregon’s ocean eat small animals classified as zooplankton. Zooplankton often eat tiny microplastics or other debris from the human environment.

That means a wayward plastic bag blowing down the beach, or those tiny bits of thread shed by your clothes in the wash can eventually end up in a whale. Or maybe in you.

While the cogs in an ecosystem’s machinery are connected, scientists who study these things often are not, often operating in separate disciplinary silos. Effective study of such interconnected problems requires egoless ecosystems of interconnected scientists.

Just such an ecosystem has emerged at Oregon State University, where a partnership of four early-career scientists from four different academic homes has developed a project to investigate connections between human-made debris, zooplankton and whales.

Termed COZI, for Coastal Oregon Zooplankton Investigation, the effort started in the whale corner of the food web. Associate professor Leigh Torres of OSU’s Marine Mammal Institute in Newport was studying the small subset of local gray whales that do not migrate to the Arctic to feed but stay in Northwest waters — the so-called Pacific Coast Feeding Group.

Why do they stay? Is the menu better here than there? She and her students began collecting zooplankton near actively feeding whales to see what they were eating.

“I had a lot of questions,” Torres said. “Do these predators prioritize one type of prey over another? What is the variation in caloric value of what they’re eating? The more we know about their food choices, the closer we get to understanding why animals show up where they do.”

Torres freely admits she is not a zooplankton expert. Luckily, she knew two at Oregon State, each with complementary expertise that could help answer her questions.

First collaborator

First was invertebrate ecologist Sarah Henkel of the Department of Integrative Biology, whose lab is near Torres’ at the Hatfield Marine Science Center in Newport. Henkel and a student began identifying species of zooplankton collected by the Torres lab at whale feeding locations. They had five years of data to work with.

“The local zooplankton communities didn’t show any differences between sites — there was no spatial pattern,” Henkel said. “So now we’re looking to see if we can relate the communities to larger oceanographic or climate factors over time,” like climate-related ocean warming.

Torres had already observed differences in whale condition over the course of years — she has developed a method that uses drone photography to essentially determine their body mass index — and those differences seem tied to climate variability. Henkel said it seems likely that these results mean that climate variability is impacting the whales’ zooplankton prey, a correlation that has been observed elsewhere in the ocean off Oregon.

While Henkel and her students described which zooplankton species were present, they also wanted to know about the nutritional value of the whales’ meals.

Enter Kim Bernard, also a zooplankton expert and an oceanographer in the College of Earth, Ocean, and Atmospheric Sciences. Bernard’s usual field sites are polar — she spent the six months of austral winter at a research station in the Antarctic to study krill a few years ago — but she was curious about the zooplankton closer to home.

She brought to the project a wealth of knowledge about collecting zooplankton, helping Torres rig sampling equipment in her small boat. She also knew how to determine caloric content of the zooplankton by using an instrument called a bomb calorimeter, which determines the energy available in an item by burning it under pressure in a highly controlled environment.

Torres and her graduate student, Lisa Hildebrand, identified six species of zooplankton in the prey samples they collected near feeding whales. Bernard’s calorimeter data revealed that the most nutritious item on the menu, which might be a factor in keeping those whales from migrating all the way to the Arctic, is Dungeness crab larvae. Uncountable zillions of the tiny proto-crabs swarm in Oregon’s coastal waters in the spring and early summer. Many end up as food for whales.

The final piece of this ecological puzzle clicked because Torres, Bernard and Henkel were curious about microplastics and other debris in the zooplankton.

An ideal, fourth partner

Just as this question loomed large, along came the ideal expert — ecotoxicologist Susanne Brander, from OSU’s Department of Fisheries, Wildlife, and Conservation Sciences.

Microplastics and other tiny debris have been found in marine species from salmon to mussels, but would they be found in Oregon zooplankton? Answering such a question is painstaking work, involving liquefying each tiny critter and examining what is left behind, much of which is of human origin — tiny pieces of plastic, fibers from clothes. Each particle is then analyzed to reveal its source material.

Much caution is required to keep the samples from being contaminated: In Brander’s lab, the lab coats are a cheerful shade of tangerine to help investigators determine whether the particles they find were shed from their own lab clothes, rather than ingested in the environment.

So far, every zooplankton sample Brander and her students have examined has contained human-produced debris of some kind, including microplastics from a variety of sources and tiny cellulose fibers from woven fabrics. From a fraction of a millimeter to several millimeters in length, the foreign particles are often huge in comparison to the size of the tiny organisms that have ingested them.

“Imagine a six-foot-tall person with two feet of rope coiled in their stomach,” Brander said.

What are the implications of this?

“If you have a piece of debris in your stomach, that’s going to mean less room for food,” Brander said. “It also may mean there’s a false sense of satiation, so that animal is less likely to go after food.”

Stuffed with plastic and fibers from our laundry, these tiny animals may starve, or at least provide less nutrition for other animals in the food web.

What does it all mean?

As is so often the case in science, answers lead to more questions. Henkel points out that now there may be multiple explanations for any observed change in caloric value of whale prey over time.

“If we see a decline over time in caloric density in the zooplankton, we need to ask, is it because of environmental conditions, or because more and more of their body weight is plastic?” she said.

The implications are not yet clear for the whales. But the researchers emphasize that it’s not just whales that eat zooplankton.

“Rockfish also eat zooplankton, and so do lingcod and other important fish in the area,” Torres said. This interconnected food web includes humans, too.

The four scientists have lots of ideas for what to do next with COZI. They may undertake additional work on the effects of climate change on zooplankton caloric value, or perhaps they’ll look more closely at microplastics in the whale poop Torres has collected, or maybe conduct lab work to look at effects of low oxygen on zooplankton.

Whatever they do, they want to do it together. It’s clear that the success of this project is partially attributable to the fact that the four scientists truly enjoy working together.

“We all know that we have something unique and valuable to bring to the table, and there’s no pushing or posturing,” Bernard said. “It’s just so easy to work with all three of them.”

• Nancy Steinberg is a science communicator in the College of Earth, Ocean, and Atmospheric Sciences at Oregon State University.
• Editor’s note: This story first appeared in the winter 2022 issue of the Oregon Stater, published by the OSU Alumni Association.