The deep impact of microplastic

 

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There’s a vast ecosystem stretching far below the ocean’s surface — one where the light dims, the pressure mounts, and life takes on forms that can seem downright alien. But even there, a place that seems a world apart from human society, our plastic trash is building up.

Scientists from the Aquarium and MBARI sampled microplastic pollution in the deep waters of Monterey Bay using the ROV Ventana. Photo courtesy MBARI

In the deep sea, it’s a challenge to study where that plastic accumulates and how it affects animals. So scientists at the Monterey Bay Aquarium and our partners at the Monterey Bay Aquarium Research Institute (MBARI) launched an ambitious collaboration.

The resulting study, which examined microplastic in the waters of Monterey Bay, was published June 6 in the journal Scientific Reports.

“We designed this study to answer a fundamental gap in our knowledge of marine plastic once it reaches the ocean,” says lead author Anela Choy, a former MBARI researcher and now a professor at the Scripps Institution of Oceanography in San Diego.

MBARI researchers collected larvaceans and their mucus feeding filters using its remotely operated vehicles. Photo courtesy MBARI.

The research team gathered data by using remotely operated vehicles (ROVs), robotic submarines designed by MBARI engineers, to collect water samples at depths from 200 to 600 meters (about 650 to 2,000 feet).

They also searched for plastic in animals with important roles in the marine food web: pelagic red crabs; and tadpole-like creatures called giant larvaceans, which surround themselves with clouds of mucus that capture food — and, as the researchers discovered, plastic.

“Problems like this are extremely complicated. To try and figure out how to solve them, you need a lot of different tools,” says Aquarium Chief Scientist Kyle Van Houtan, who co-authored the paper with Anela and nine others, tapping fields from physical chemistry to marine ecology. Continue reading The deep impact of microplastic

Untangling the mysteries of deep-sea food webs

Stretching more than two vertical miles from the seafloor to the ocean’s surface, the water column is Earth’s biggest habitat by volume. For researchers trying to untangle its complex, multi-tentacled food web—the way energy flows from one ocean denizen to the next—it’s a vast and challenging realm in which to accomplish this task.

A gonatid squid eats a deep-sea fish. These types of predator-prey relationships were easier to document, leading marine biologists to undervalue the “who eats who” complexity of predation by more delicate gelatinous animals. Photo © MBARI

Recent work by scientists at the Monterey Bay Aquarium Research Institute (MBARI) has revealed whole new layers of predator-prey interactions in the water column, particularly in the often overlooked roles played by jellies and other soft-bodied animals—many of which, researchers discovered, feed on their own kind.

This research is promising, says Anela Choy, the biological oceanographer who led the study, but much more remains to be discovered about deep-sea food webs.

“I wish I knew just how much there was that we didn’t know,” she says. “That’s what keeps us all going.”

New appreciation for jellies

Many feeding interactions in the deep sea are difficult to observe because they take place in total darkness, thousands of feet below the surface, in cold, crushing conditions that test even the capacities of MBARI’s advanced robots. Before the advent of robotic exploration technology, much of what scientists gleaned about food webs was gathered from animals hauled to the surface in nets—or discovered in a predator’s guts.

High-definition video cameras captured this image of a helmet jelly eating two types of prey: a small squid and (on its bell) another species of jelly. Photo © MBARI

One problem with that approach, Anela says, is that squishy animals like jellyfish and other gelata, while among the most prevalent life forms in this ecosystem, almost never make it to the surface intact.

“They’re really hard to capture—that’s the traditional way of studying diet, is to capture those animals and look in their stomachs,” she says. “With a net, they often immediately break apart. “If they are the predator of interest, we cannot ascertain their gut contents this way because they are very damaged.”

Obstacles to overcome

There are other obstacles to understanding food webs. The traditional way of studying diet is to capture an animal and look into its stomach to see what prey have been eaten. Anela notes that gelata digest very quickly and thus are often missed with diet work.

MBARI’s remotely operated vehicles, like the Doc Ricketts, have recorded video documenting hundreds of feeding interactions in the deep sea. Photo © MBARI

So Anela and her MBARI co-authors, Steve Haddock and Bruce Robison, tried a different approach.

The high-definition cameras on MBARI’s diving robots have recorded thousands of deep-sea animal observations since 1989. All of the video has been rigorously archived to reflect its subject, location, time, depth and even water temperature and other physical parameters. From this footage, Anela and her colleagues gleaned a wealth of information: 743 documented instances of undersea creatures eating, being eaten, or having just fed.

(Anela singled out two video technicians at MBARI, Susan von Thun and Kyra Schlining, who “watched every single hour of videotape from every midwater dive” to build an unprecedented underwater feeding dataset.)

Hundreds of feeding observations

From the video, the team tallied 242 unique kinds of predator-prey relationships. Many involved jellyfish and other soft-bodied animals, which don’t seem to particularly mind having a robot watch them eat, and which are often transparent, meaning the researchers could easily peer inside their bodies to view their most recent meal.

This complex food web shows groups of animals (indicated by different colored circles and lines) that were observed eating each other during MBARI remotely operated vehicle dives. Thicker lines indicate more commonly observed predator/prey interactions. Illustration © 2017 MBARI

In their published study, they documented the complexity of predator-prey relationships they uncovered from this treasure trove of data.

A key illustration from the study draws lines showing predator-prey interactions between 20 different functional groups seen feeding on each other in the footage, from fish to crustaceans to jellies to cephalopods like squid. Fittingly, the resulting tangle of colorful who-eats-whom lines resembles a jellyfish.

“Jellyfish get kind of a bad rap,” Anela says, noting that some biologists cast them as nuisances—trophic dead ends that don’t feed back into the food web.

“This shows something totally different,” she says.” It shows they’re central parts of deep sea ecosystems, with really diverse diets and serving as both predators and prey.”

One species of jellyfish was observed eating 22 different kinds of prey.

(In the figure, many of predator-prey nodes loop back on themselves. “That,” says Anela, “is cannibalism—species within those broad animal groups feeding on one another.”)

There’s more to come

“Our method gives you a totally different view of the interactions going on in the food web,” Steve Haddock says.

The transparent bodies of animals like this medusa jelly let researchers peek into their guts and discover what they’ve been eating — in this case, a red mysid shrimp. Photo © MBARI

It’s a bit like going from a map with only train tracks to one that includes highways, he says: “You feel like things are connected in only a certain way, but suddenly you see these other connections. This study really complements and expands our view of what’s going on in the ocean.”

Still, Steve says there’s much left to learn.

“Even though this method has revealed a large diversity of interactions, there’s still a whole other universe of interactions we haven’t discovered,” he says.

The next layer of discovery may not come from video observations. Steve sees great promise in techniques like analyzing predators’ gut DNA for hints about their recent meals. Another avenue that is already widely utilized is compound-specific stable isotope analysis, which looks for chemical signatures that might accumulate in a creature’s tissue from eating certain prey.

Jellies often eat other jellies, as is the case with this red medusa preying on a siphonophore. Researchers documented some animals that fed on 20 or more prey species. Photo © MBARI

(That’s the approach used in a recent study by Aquarium researchers to document changes in North Pacific seabird diets over the past 130 years.)

“There will continue to be a lot more revelations about food web connections,” Steve says.

Anela agrees: “You hear that the deep sea is like outer space—it’s so poorly known and so poorly explored, every time we go down there we learn new things. All of that is true. But really, understanding that food webs tie everything in the ocean together is the reason I study them.”

Our ever-growing understanding of those connections, she says, will be critical to stewarding the ocean in the future.

—Daniel Potter

Choy, C.A., Haddock, S.H.D., Robison, B.H. (2017). Deep pelagic food web structure as revealed by in situ feeding observationsProceedings of the Royal Society B. 284: 20172116, doi: 

Pinpointing plastic’s path to the deep sea

Until now, little has been known about how microplastics move in the ocean. A new paper by our colleagues at the Monterey Bay Aquarium Research Institute (MBARI), just published in the journal Science Advances, shows that filter-feeding animals called giant larvaceans collect and consume microplastic particles in the deep sea.

Larvaceans are transparent tunicates that live in the open sea and capture food in sticky mucus filters. Plastic particles accumulate in the cast-off mucus feeding filters and are passed into the animals’ fecal pellets, which sink rapidly through the water, potentially carrying microplastics to the deep seafloor.

Researchers at MBARI documented that tadpole-like giant larvaceans consume microplastic beaads. Photo courtesy MBARI.

The new findings contribute to an emerging picture about the ubiquitous nature of ocean plastic pollution. Over the last decade, scientists have discovered tiny pieces of plastic in all parts of the ocean—including deep-sea mud. One recent study documented microplastic fibers in deep-sea sediments at levels four times greater than an earlier study had found in surface waters. Plastic has also been discovered in the tissues of animals at the base of the ocean food web. Another just-published study found that fish confuse plastic particles with real food items because it smells just like organic matter in the ocean.

Despite their name, giant larvaceans are less than 10 millimeters (4 inches) long, and look somewhat like transparent tadpoles. Their mucus filters—called “houses” because the larvaceans live inside them—can be more than 1 meter (3 feet) across. These filters trap tiny particles of drifting debris, which the larvacean eats. When a larvacean’s house becomes clogged with debris, the animal abandons the structure and it sinks toward the seafloor.

Principal Engineer Kakani Katija studies giant larvaceans during field expeditions in Monterey Bay. Photo courtesy MBARI.

In early 2016, MBARI Principal Engineer Kakani Katija was planning an experiment using the DeepPIV system to figure out how quickly giant larvaceans could filter seawater, and what size particles they could capture in their filters. Other researchers have tried to answer these questions in the laboratory by placing tiny plastic beads into tanks with smaller larvaceans. Because giant larvacean houses are too big to study in the lab, Kakani decided to perform similar experiments in the open ocean, using MBARI’s remotely operated vehicles (ROVs).

When she discussed this experiment with Postdoctoral Fellow Anela Choy—who studies the movement of plastic through the ocean—they realized that in-situ feeding experiments using plastic beads could also shine light on the fate of microplastics in the deep sea. Continue reading Pinpointing plastic’s path to the deep sea