Geo-Joint: Pelagic Pyrosomes Present to the Playa

Source: Wikimedia: EncMstr (CC 4.0)

You never know what you’ll find at the beach. Just about anything man-made can wash up, and you’ll always find the local shells and kelp. When the currents sometimes wander a little off course and the winds take odd turns, unexpected items can roll in with the waves. Recently, Pacific Coast beachwalkers from Oregon north to British Columbia have been noticing the arrival of large numbers of bumpy, gelatinous tubes on their shores, most about the length and diameter of your finger. Pinkish to yellowish in color and translucent, they seem to be made of many little cells. In fact, each little spot inside the mass is an individual—a zooid—contributing to what is called a colonial tunicate. Tunicates also come in a larger, singular form, and are often found attached to rocks, docks, or boats. Commonly called “sea squirts,” they are fairly simple animals that draw water into their sac-shaped bodies and filter out plankton. If you poke them when they are out of water, you will see that they do indeed squirt. Because they have a nerve stem called a notochord, they are taxonomically in the Phylum Chordata, the same one you are in (unless you are a spineless wimp).

Source: Wikimedia: Show_ryu (CC 3.0)

The oddities showing up on Pacific Northwest beaches are not these larger individuals, but a colonial variety called Pyrosoma atlanticum. Hundreds to thousands of tiny individuals only a few millimeters across make up the rigid, rubbery structure, which is hollow inside, and closed at one end. Each member of the colony draws in water from the outside surface, beating it with hair-like cilia and driving it through a mucus net which collects plankton to eat. The water then moves to the interior of the tube and is pushed out the open end, which simultaneously generates movement through the ocean in a kind of slow-motion jet. Their movement isn’t directed by a central brain in a head of any kind, but overall, the colony has something directing it to rise in the water column during dark hours, and sink lower in the day, ranging from near surface levels down to 800 to 2,500 feet deep in a daily cycle. These small tubular colonial tunicates hang around in large groups, usually far out in the open ocean, hence they are called colonial pelagic tunicates. They don’t come ashore on purpose, but are carried there by the forces of wind and current. Once they turn up on the sand, they are most likely dead, and no longer exhibit one of their striking qualities—their ability to bioluminesce. And that’s where they get their name: pyrosoma means “fire body” in Greek, a reference to the glowing light they can give off. It is thought that this capability helps pyrosomes attract zooplankton at night.

Source: Flickr: Biodiversity Heritage Library (Public Domain)

Most of the recently washed-up Pyrosoma antlanticum range to about three inches in length, but they can be more than 20 inches long. They are found in a broad swath of the world’s oceans, generally from 50 degrees north latitude, to 50 degrees south, from temperate to tropical zones. Fellow pyrosome species far surpass them in size: Pyrosoma spinosum, a tropical species, can reach a length of 60 feet, with a tube aperture that may be over six feet across! Combining such a huge and bizarrely shaped creature with the bright neon, blue-green glow of bioluminescence would make for a decidedly otherworldly encounter. Described as soft as a feather boa, these large pyrosomes react to touch by glowing. Unlike most other bioluminescent marine animals, pyrosomes glow in response not only to physical stimulation, but as a reaction to light itself. Individual members of a colony will incite one another to glow, and the incentive to light will also pass from one colony to the next. The brightness and persistence of their output is notably strong compared to other luminous denizens of the sea.

Making the oddness of pyrosomes that much odder is that all the individual zooids are clones of one another. If part of the organism is damaged or eaten, those remaining create copies of themselves to fill in, or simply to increase the size of the the colony. In this way the floating tube has a theoretically immortal chain of existence. What must life be like, gliding and munching slowly through the ocean, defenseless, glowing, and sharing a body structure with thousands of comarades who are just like you? The variety of nature’s designs for existence are truly staggering. And to think that for most of us, only the accidents of shifting winds and currents bring these creatures to our land-based awareness. What else is out there?


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