Invasion of glowing tropical jellyfish baffles U.S. scientists

By Matthew O. Berger, Oceans Deeply
Thousands of pyrosomes encountered off the Oregon coast. Photo by Hilarie Sorensen/University of Oregon via NOAA
1 of 2 | Thousands of pyrosomes encountered off the Oregon coast. Photo by Hilarie Sorensen/University of Oregon via NOAA

Aug. 9 (UPI) -- Hilarie Sorensen intended to do her master's thesis on crystal jellyfish, the half moon-shaped bioluminescent jellies that are ubiquitous off the West Coast. Instead she'll be researching a jelly-like creature she hadn't heard of before May.

That was when the University of Oregon marine biology graduate student went on a two-week research cruise from San Francisco to Newport, Ore. "In pretty much every single station, all we would get were pyrosomes," she said.


Pyrosomes look like a type of jellyfish but are actually colonies of tiny glowing animals usually found in tropical and subtropical oceans. But in recent years they've appeared in the millions off the coasts of Oregon, Washington, British Columbia and Alaska.

This isn't the first year pyrosomes have appeared off the Northwest. "From 2015, we started [seeing] them in larger numbers. And 2016 was even larger. But then in February, we saw huge numbers, and in May even more," said Samantha Zeman, a research associate at Oregon State University who was also on the May cruise and has been monitoring the pyrosome boom.


Some of the researchers on the cruise with Sorensen had seen them earlier in the year. But even those who had were struck by the sheer numbers of pyrosomes.

"It was pretty much the only thing we would catch," Sorensen said. "What became increasingly frustrating was that there was so many of them. We just kept seeing more and more of them the further north and further offshore we went."

A GoPro camera attached to a net was sent down to 330 feet. "When we plugged in that video and looked at it on the screen the entire view was just pyrosomes. There was nothing else," she said, estimating there were a thousand of the gelatinous, tube-shaped creatures just within that frame. The average length of the ones pulled up was just over 10 inches, though they ranged from a few inches to over a foot.

Why they're there, whether they'll be back in future years and what impacts they'll have on ecosystems and fisheries that haven't seen these animals before are all questions researchers like Sorensen didn't even know were worth trying to answer a couple months ago.

She's focusing on determining what environmental conditions - salinity, temperature - appear to lead to an abundance of the newcomers. In short, why are they here?


The general hypothesis has been that the usually tropical species showed up because of recent warm water temperatures - in particular, "the Blob," a mass of warm water that persisted off the West Coast from 2014 to 2016. Although Sorensen is "sure the story is much more complicated than that."

But there are many more questions to answer.

For instance, Sorensen noted that some researchers have been dragging a bottom trawl along the sea floor and bringing up scores of dead pyrosomes. Other huge booms in a certain species, like algae, are followed by equally huge die-offs that consume dissolved oxygen as the animals decompose, leading to oxygen-deficient swathes of ocean. Could that pyrosome-caused dead zone become a new part of ocean cycles in the northeastern Pacific?

"I would not be surprised if in the next few months we see a lot of proposals going in for new research," Sorensen said.

One question they'll try to answer is how much phytoplankton they're eating - and whether that's impacting the rest of the food web. "They're eating huge quantities of primary producers," said Sorensen. "If they do continue to show up, what's going to be the impact of that in terms of primary production?"


And then there's the matter of what's eating them.

"It is amazing to see them coming out of black cod," Linda Behnken, executive director of the Alaska Longline Fishermen's Association, said from her fishing boat off Sitka, Alaska, last week, where she was long-lining for black cod. That means the bottom-dwelling fish were eating the pyrosomes; surprising since pyrosomes are generally thought to stay near the sea's surface.

"They must be thick from surface to deep," Behnken added.

Zeman noted that fin whales and rockfish are known to eat them, too. "Though I'm not sure how much nutrition they have - they probably have to eat a lot, and maybe can't digest them," she added.

Behnken isn't the only one encountering them in Alaska this year. A crab boat reported seeing thousands of pyrosomes illuminated in its lights on March 18 in the Chatham Strait, east of Baranof Island, home to Sitka, according to a map compiled by local fishers. A black cod long liner reported "fairly dense concentrations from the surface down" March 22 on the other side of the island. A salmon boat reported "clusters on troll gear" at the southern tip of the island April 15. When king salmon season opened in early July, one fisher reported picking 20 to 30 pyrosomes off the gear daily during a four-day period; the largest one was 1 foot long, though none were found in the salmon's stomachs.


Compare that to last year, when Alaska fishers didn't know what the jelly-like newcomers were. Alyssa Russell was on a boat that pulled up pyrosomes constantly - at least a dozen or two a day - while trolling for salmon last summer near Sitka. "The captain said, 'I've never seen this before,'" she said.

She said that they didn't seem to be tangling gear or causing problems, and Behnken said the pyrosomes weren't slowing down her black cod fishing this year. But there have been reports that early this spring the pyrosomes were so abundant and getting caught in gear so often that some fishers in Alaska and Oregon stopped fishing for a while.

Down off the Oregon coast, things have calmed down a bit. Sorensen said they stopped washing up on beaches and there haven't been many near shore since the beginning of June - which happens to be when the yearly upwelling of cold, deep waters started.

But she said they have still been coming up in nets offshore, 85 miles out or farther. She's going back out on a research cruise Friday, to gather some more clues about why the newcomers showed up - and whether they'll be back.


This article originally appeared on Oceans Deeply, and you can find the original here. For important news about ocean health, you can sign up to the Oceans Deeply email list.

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