What weird new parasites on Antarctic fish tell us about climate change around the world

The seas are rough in Antarctica, where the scientists start fishing at midnight. 

Water washes over the deck as the ship rocks back and forth. In storms like this, the first mate tells the crew to stay in.

“Everyone inside except the scientists!” he calls. 

That’s when John Postlethwait and his team get to work.

Under the glare of the deck lights, the researchers unload a 30-foot trawl to add to their growing pile of fishes, sea stars, marine worms, octopuses and all other manner of undersea creatures. They sort through the catch to find what they’re looking for, a species of fish that the National Science Foundation has commissioned them to study.

But on this particular night, back in 2018, a different species caught the team’s attention. They started noticing ice fish called notothens coming out of the trawl with something unusual: bumpy pink tumors that bulged out of their heads, bodies and fins.

“When we first saw it, we were shocked,” said Postlethwait, a professor of biology at the University of Oregon. “We didn't know what it was.”

It wasn’t what they’d set out to investigate, but the team made a snap decision to start collecting the diseased notothens. They quarantined the fish, as many as would fit in six big aquaria, away from the other specimens. Eventually, they set sail back to Oregon, where they could try to make sense of what they’d seen.

It was a pathological mystery on the high seas that soon caught the interest of Arvind Varsani, a virologist at Arizona State University. And though the Antarctic ocean might seem farther from Arizona than any other place on Earth, he and the Oregon-based researchers soon found connections that transcended geography and academic disciplines.

They learned lessons about climate change research in far-reaching icy landscapes that have implications for parasite studies in drought-stricken Western reservoirs, as well as for the future of science communication.  

Their findings, recently published in the journal iScience, resulted in the naming of a never-before-seen single-cell organism. They also set the groundwork for a whole new set of research questions the team is eager to study.

“I think this is important because it highlights the dynamics at play in our ecosystems,” Varsani said. “One slight change or a sequence of changes in an ecosystem could have major consequences.”

A team effort spanning continents and approaches

Varsani’s quest to help uncover the origin of the fish tumors didn’t start with fish. It started with penguins.

He had done research in the Antarctic in the past, working closely with a collaborator at Oregon State University to study viruses in Adélie and chinstrap penguins, but on the opposite end of the Southern pole from Palmer Station, where Postlethwait and his team were based.

So when Varsani went to Oregon State to give a seminar on his work, one of Postlethwait’s teammates, a fish biologist named Thomas Desvignes, drove an hour from Eugene to Corvallis to describe the apparent outbreak they had observed. 

Desvignes told Varsani that over 30% of the notothens they’d seen had tumors. Of the 14 long-term Antarctic fish researchers they’d asked about it, only four had ever seen such tumors before, and they had only seen them in a few fish at a time. No one had ever seen them in such large numbers. 

One meeting turned into a series of meetings, and eventually Postlethwait rallied the group to put together a new proposal to the National Science Foundation to study the outbreak.

Once their proposal was approved, the team got to work. Varsani was convinced that a virus must be causing the tumors, so Postlethwait shipped him specimens: five-millimeter by five-millimeter squares of diseased and healthy fish tissue. 

Varsani’s team broke down those tiny squares even more in a process called macerating, which he said serves to “separate all the cells and mush it up so that the cells break.” From there, they added a few more ingredients so they could extract the nucleic acids, substances that scientists can use to pull out genetic sequences. 

It’s similar to the technology that powers COVID-19 variant monitoring, a combination of lab machines and computer programs that help researchers read each unique letter on a strand of genetic code. 

Varsani had hoped sifting through the different genetic clues in the tissue samples would reveal the cause of the tumors. But to his surprise, he didn’t find any viruses.

“I was disappointed, I'll be honest,” he said. But his collaborator, Desvignes, didn’t give up hope. “I was looking at the data … very much from a viral lens. And (Desvignes) was like, ‘Oh, what else could be there?’”

Desvignes took a methodical approach, looking for patterns in the piles of nucleic acid data. Once he started noticing some repeated sequences, he initiated additional molecular tests.

Those tests revealed that the pathogen of interest was not a virus, but a newly-discovered type of single-cell parasite that somewhat resembles existing fish parasites. 

It was a discovery that required teamwork, multiple approaches, and dedication from all the collaborators, Varsani said.

“I really admire the way that he looked through those sequences and narrowed down and found that it was these special alveoli, the single-cell organism that causes this,” he said.

Considering the climate culprit

Once the scientists had successfully zoomed in on this single-cell microbe, which they named Notoxcellia, as the culprit behind the tumors, their next step was to zoom back out, way out, and think about what might have caused this new situation.

As with any pathological mystery, on the high seas or otherwise, solving it starts with considering all the possible suspects. Antarctica is vast, and research there is logistically difficult. It could simply be that no one had come across a Notoxcellia outbreak before.

But given how prevalent the tumors were among the notothens caught that day, it’s much more likely that something in the environment shifted, causing these two organisms to interact under new circumstances. And, in Antarctica, any mention of something shifting immediately brings to mind massive, melting glaciers.

“You'd expect more of this in the regions where the water is increasing in temperature, but also decreasing in salinity with the melting of the ice caps,” Postlethwait said.

Polar regions are some of the fastest-warming places on the planet. As extreme environments in all ways, they also have high natural climate variability. But scientists have been able to demonstrate — through models tracking how greenhouse gases have influenced the warming of air in the tropics that is then pushed over the South Pole — that human-caused climate change is behind parts of Antarctica warming at three times the rate of the global average over the past 30 years. 

This warming creates new conditions and new opportunities for disease vectors to spread into habitats they didn’t previously occupy, where they might interact with new animal hosts that may also be venturing into uncharted territory in search of food or shelter or cooler waters.

It’s a climate change pattern that has been documented by scientists many times already, with the Centers for Disease Control and Prevention actively monitoring the northward spread of threats like Lyme disease and Valley Fever as milder winters and warmer summers favor their expansion.

For the notothens, it becomes a perfect high seas storm. Humans burn fossil fuels, releasing greenhouse gases that trap heat and energy from the sun in the atmosphere. The atmospheric energy boost generates stronger winds that push the warmed air over Antarctica, causing fresh water to trickle out of the ice caps and into the sea. This melting dilutes the salts and warms the water, changing the conditions in which Antarctic marine life has evolved. And as fish struggle to adapt to a shifting environment, they become less able to fend off parasitic invasions.

“With any kind of an environmental stress, you’re more susceptible to disease, but you're also not going to perform the best," Varsani said. "And so those kinds of things are very important for us to know even though this might not have implications to humans. It does have major implications within the ecosystem perspective.”

Varsani then brought it back to penguins. Notothens make up about 95% of the biomass of fish in Antarctic waters, and are a major food source for some species of penguins, sea lions and elephant seals, the scientists said. If this group of fish succumbs to a bizarre new skin-tumor-parasite disease, those animals, which are already experiencing stress from rising temperatures in other ways, may disappear.

And the fish don’t have to succumb entirely for the tumors to have a ripple effect all the way up the Antarctic food chain. The scientists measured all the notothens they caught that day in 2018 and compared the size of those with tumors to those without. The fish infected with the parasite were smaller, on average. That can affect their reproductive output and suggests that a future in which Notoxcellia is a climate change winner may mean less food overall in Antarctic waters.

Such a change is exactly what the scientists predict. They are already brainstorming ways to test the theory, by looking to the past to paint a clearer picture of what may lie ahead.

“Going into the future, you would expect to see more of these things in the places that are warming the fastest,” Postlethwait said. “Another thing that you could do would be to go back into museum samples. You would predict that in the past, before global climate change became so evident, there will be a lot fewer of these organisms found than today or in the future.”

Cross-continent comparisons

In a vastly different body of water much closer to home, another group of scientists have been surveying the fish parasites in Lake Powell, one of two major reservoirs on the Colorado River. They want to create the kind of record Postlethwait, in his own work, says is necessary to go back in time and identify what has changed. 

Mark Belk, a professor of biology at Brigham Young University in Utah, was more than happy to oversee this effort. Whereas fishing in Antarctica takes a “whole lot of work because (the fish) are down deep and it’s cold,” he says, fishing in Lake Powell is “like a party at Christmas.”

Belk beamed at his luck in becoming a biologist who gets to fish in beautiful places for a living.

“Lake Powell is a fun place to go, and especially to do research there is even more fun,” he said. “Then we bring them back and we’re processing and dissecting fish. Every fish you open has new parasites and you’re going around like ‘oh wow, look at this!’ Parasites are the most interesting stuff that nobody knows about.”

Belk and colleagues took students out to help catch and evaluate fish in Lake Powell in April 2013 and 2015. Their survey, published in 2017 in the journal Western North American Naturalist, turned up 13 species of parasites affecting 8 different species of fish and became the first record of fish parasitism in Lake Powell.

Just five years later, Lake Powell is already a very different place. A record 22-year drought combined with increased evaporation due to rising average temperatures has been chipping away at flows in the Colorado River. The reservoir is at its lowest level since it first filled, and dropping. Belk says this is almost certainly hurting fish in a number of ways.

“When you get this megadrought that we're in right now, the water level goes down and down and down. And what that does is create really difficult, stressful conditions for the fish population,” Belk said. “I will almost guarantee you that the incidence of parasites has gone way up, and the abundance, and the average number that are found in each fish. And I'll bet you'd find several more of those fish that are highly infected. So it's like when it rains, it pours.”

Related: As Lake Powell drains, questions surface about its future

Surviving as a fish is a numbers game, Belk says. A fish tries to maintain as much distance as possible from its predators and parasites. But as Lake Powell shrinks, so do the opportunities for its fish to avoid a disastrous fate. 

On top of that, smaller bodies of water warm up faster and concentrate solutes at higher rates. While the fish in Antarctica are struggling with melting fresh water from ice caps diluting the ocean salts, the fish in Lake Powell have to contend with less fresh water resulting in greater exposure to toxins and higher concentrations of salts.

Either way, the pace of all this change is faster than the rate at which fishes can evolve, piling on the environmental stressors they must deal with and the ways climate change may be tilting the odds in favor of their parasites.

Sketching the way forward

To know for sure how fish parasitism is changing over time in parallel with climate change, future work will have to replicate the surveys in the Antarctic and Lake Powell and compare those findings to the baselines established by both of these studies.

Just as Varsani advocates for the importance of science he thinks some view as mundane if it doesn’t cure a human ailment, Belk believes doing routine surveys in nature is an essential, if less flashy, step toward understanding how climate change is altering our world.

“You’d be amazed at the number of places where nobody has ever gone and looked at ‘what are the parasites here?’” Belk said. “There's a lot of good descriptive work that needs to be done just on the fish. But (in many places) nobody's even touched the parasites. There are cool parasites just waiting for you to tell their life story.”

The Antarctic researchers also believe that describing changes in the natural world through science doesn’t stop at numbers and charts. It’s important to find new ways to tell the story, not only of new parasites as they are discovered, but of how scientists know that climate change plays a role.

That’s where Chloe DaMommio comes in. The recent University of Oregon graduate already had one science comic under their belt when the Antarctic team asked if they’d like to draw one about the new fish tumor paper. As a marine science major, it seemed like an opportunity for DaMommio to merge their interests in science and art while helping bridge the gap between those disciplines for others, to more broadly communicate the research.

“I'd never heard of this kind of parasite that presents as a tumor,” DaMommio said. “And I didn't know a lot about Antarctica. It's a landscape that is very dominated by light, because it is fairly monochrome. You have a lot of black stone and a lot of light snow and ice, some blues. It’s a landscape that's very visually interesting.”

DaMommio applied this artist lens to the Antarctic fish research story and produced a 16-frame illustration that adds a human touch, depicting the researchers dressed in orange weatherproof clothing aboard a bright red research vessel. It has been translated into Spanish, French, Danish and German as part of the research team’s effort to communicate possible effects of climate change to people who may not otherwise get the message.

“I think frankly, most of the time, it takes something big and deeply human to change (someone’s mind),” DaMommio said. “I think the main goal with this type of media is not necessarily to completely change someone's outlook, but to make content that people want. There are a lot of people that want to know this stuff who can't read those articles because they don't have a background in that specific field.”

Independent coverage of bioscience in Arizona is supported by a grant from the Flinn Foundation.

Melina Walling is a bioscience reporter who covers COVID-19, health, technology, agriculture and the environment. You can contact her via email at mwalling@gannett.com or on Twitter @MelinaWalling.

Joan Meiners is the climate news and storytelling reporter at The Arizona Republic and azcentral. Before becoming a journalist, she completed a doctorate in ecology. Follow Joan on Twitter @beecycles or email her at joan.meiners@arizonarepublic.com.

Please support science coverage and local journalism by subscribing to azcentral.com at this link.