Natural wonders: Pyrosomes »Explorersweb

Pyrosomes are often referred to as the “unicorns of the sea”. Why? Because we hardly know anything about them. Since 2013, they’ve made several appearances, and scientists have only scratched the surface of what these creatures are. They are elusive, mysterious, alien-like, and completely harmless.

A small pyrosome found in Oregon. Photo: Alexander Clay Detweiler / Shutterstock


French explorer François Peron first discovered pyrosomes in the early 1800s. The word “pyrosome” in Greek means “body of fire”, referring to its bioluminescent characteristics. While a pyrosome looks like a single creature, it is actually made up of thousands. It is a colony of millimeter long “zooids”, which are invertebrates. These zooids come together to form a gelatinous tubular body that can range from a few centimeters to 18 m.

A hollow center

Some pyrosomes have a hollow center large enough to house smaller creatures like fish and shrimp or even for a human to swim through. In addition to being home to other marine animals, pyrosomes also feed turtles, birds, and fish, as well as seabed dwellers. Observers saw crabs and eels feeding on dead pyrosomes on the ocean floor.

Most species of pyrosomes are found in tropical waters, but a few types have appeared in cooler regions, including Antarctica. Individual zooids reproduce asexually because they are hermaphroditic in nature. This means that they clone each other, which comes in handy when parts of the body are missing. In a way, pyrosomes are capable of being immortal.

A wormhole in the Delta quadrant? No, a close-up of the mouth of a pyrosome. Photo: dlearyous photography / Shutterstock


They emit light, like fireflies

In the dark, pyrosomes, via their individual zooids, emit light when stimulated by an enzyme called luciferase. This is the same enzyme found in fireflies. They light up when other zooids report them. Sometimes this communication creates a wave of blue, red and green light up and down the tube. They also emit light when threatened. In daylight, they have a slightly pink, blue or yellow color.

Pyrosomes are not harmful to humans because they are above all filter feeders. As it drifts like a worm in the ocean, it feasts on microscopic plankton, filtering water through its gelatinous skin. Scientists have found that the filtration process allows the pyrosome to propel itself forward very slowly. Zooids create a “feed stream”, pushing out water to create tiny movements. Pyrosomes usually live in the upper layers of the sea.

The pyrosome can migrate 410m per day. Scientists have found that the behavior of pyrosomes changes with depth and time of day. After sunset, they descend to about 700m before going up again in the morning.

Plunger and pyrosome. Photo: dlearyous photography / Shutterstock


The hot drop

Researchers have started to link pyrosomes and climate change. In 2013, they began to appear when the waters around the west coast of the United States experienced warmer temperatures. Authorities called it the “hot spot.”

Thousands of pyrosomes managed to drift into the Columbia River and severely affected the salmon fishing industry. A few years later, in 2016 and 2017, they reappeared in this area, as well as in Alaska. This may be related to rising temperatures, in the same way that other larger animals are also expanding their range into once inhospitable areas.

About the Author

Kristine De Abreu

Kristine De Abreu

Kristine De Abreu is a writer (and occasional photographer) based in sunny Trinidad and Tobago.

Since graduating with a BA in English and History from the University of Leicester, she has pursued a full-time writing career, exploring several niches before embarking on travel and exploration. While studying for an additional travel journalism degree with the British College of Journalism, she began writing for ExWeb.

Currently, she works for a travel magazine in Trinidad as an editorial assistant and is also ExWeb’s Weird Wonder Woman, reporting on the world’s natural quirks as well as general stories from the world of exploration.

Although not a climber (yet!), She hikes in the bush, is known to befriend iguanas, and quotes The Lord of the Rings trilogy from start to finish.

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