Amusing Monday: Odd-looking pyrosomes more familiar in the tropics

“I have just watched the moon set in all her glory, and looked at those lesser moons, the beautiful Pyrosoma, shining like white-hot cylinders in the water.”English biologist Thomas H. Huxley, 1849

Warmer-than-normal waters off the coast of Oregon, Washington and British Columbia may be responsible for an invasion of all sorts of creatures normally found to the south in more tropical waters. None of these animals has attracted more attention than the bright bioluminescent pyrosomes, which showed up last spring as the waters of the Pacific Ocean were returning to normal temperatures.

Pyrosomes — which comes from the Greek word “pyro,” meaning fire, and “soma,” meaning body —are large colonies of small tunicates. These are invertebrates that feed by filtering sea water. The individual tunicates, called zooids, hook together to form tubes. The intake siphon of each zooid is aligned to the outside of the tube, while each discharge siphon is aligned to the inside.

The pyrosomes seen in Northwest waters so far are relatively small, thus fitting their nickname “sea pickles.” Nevertheless, they have impressed scientists who have observed them. The first video, above, was made in late July during the 2017 Nautilus Expedition along the West Coast (Water Ways, Sept. 4).

Hilarie Sorensen, a University of Oregon graduate student, participated in a research cruise in May, traveling from San Francisco to Newport in search of jellyfish that had invaded Northwest waters over the previous two years. She didn’t find the jellies she hoped to see, but she was blown away by the pyrosomes, some more than two feet long, and she wondered what they were up to.

“I am interested in how short- and long-term physical changes in the ocean impact biology,” Hilary was quoted as saying in a UO news release. “With all of these pyrosomes this year, I would like to further explore the relationship between their distribution, size and abundance with local environmental conditions.”

Reporter Craig Welch wrote about the recent findings for National Geographic. He quoted Laurie Weitkamp, a biologist with NOAA’s Northwest Fisheries Science Center: “For something that’s never really been here before, the densities are just mind-boggling,” she said. “We’re just scratching our heads.”

Even more impressive are the giant pyrosomes that have not shown up in Northwest waters, at least so far. They are rare even in tropical locales. Check out the second video, which shows a pyrosome found in the Canary Islands in North Africa and estimated to be about 12 feet long.

The third video was filmed in Tasmania south of Australia by Michael Baron of Eaglehawk Dive Centre. It shows both a giant pyrosome and a salp, another colonial creature formed of larger individuals. For the full story on the pyrosome, go to the BBC Two program, “Unidentified glowing object: nature’s weirdest events.”

Another good video on YouTube shows a giant pyrosome in the Maldive Islands off southern India.

Oddly enough, pyrosomes seem to light up in response to light, according to information posted on an invertebrate zoology blog at the University of California at Davis. The colonies may also light up in response to electrical stimulation or physical prodding.

When an individual zooid has activated its luminescence, it will trigger a chain reaction throughout the colony with nearby zooids lighting up in turn.

“When many pyrosomes are present in the same general area it’s possible to observe a vivid array of bright, pale lights produced by the many animals,” said Ian Streiter in the blog post.

“It was just this sort of observation that led the great Thomas Huxley (‘Darwin’s Bulldog’) to remark in 1849: ‘I have just watched the moon set in all her glory, and looked at those lesser moons, the beautiful Pyrosoma, shining like white-hot cylinders in the water.’

Ian concluded, “For those lucky enough to be at sea when they’re around, I imagine there are few sights as pleasant as that of the ‘moonlight’ produced by the fire bodies.”

Other information:

Finally, there is this audio report, “Millions of tropical sea creatures invade waters off B.C. coast,” with commentary from Washington state fisherman Dobie Lyons and zooplankton taxonomist Moira Galbraith of the Institute of Ocean Sciences in Sidney, B.C. They appeared on All Points West, CBC Radio, with Jason D’Souza of Victoria.

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