What Is a Pyrosome and How Can It Grow 60 Feet Long?

A pyrosome is a colonial marine organism made up of thousands of tiny individual animals called zooids that fuse together to form a single hollow, tube-shaped creature that can reach over 60 feet in length. Despite appearing as one massive organism, each pyrosome is actually a superorganism where thousands of genetically identical clones work together as a unified living system.

The Structure of a Living Tube

The name “pyrosome” comes from the Greek words “pyros” (fire) and “soma” (body), referring to their remarkable ability to produce bioluminescent light. Each pyrosome consists of hundreds to thousands of individual zooids, each only a few millimeters long, that are embedded in a shared gelatinous tunic. These zooids arrange themselves to form a hollow cylindrical tube that remains open at one end and closed at the other.

The individual zooids are actually tunicates, making pyrosomes more closely related to vertebrates than to jellyfish or coral. This surprising evolutionary relationship places them in the same phylum (Chordata) as humans, fish, and all other animals with backbones.

Jet Propulsion Through Teamwork

Pyrosomes move through the ocean using a sophisticated form of jet propulsion. Each zooid continuously pumps seawater through its body, filtering out tiny organisms and particles for food. The filtered water is then expelled into the central cavity of the tube. When thousands of zooids coordinate this process, they create a powerful water jet that propels the entire colony through the ocean.

This synchronized movement allows pyrosomes to migrate vertically in the water column, often rising to surface waters at night to feed on plankton and descending to deeper waters during the day.

Bioluminescent Fire Bodies

One of the most spectacular features of pyrosomes is their ability to produce brilliant bioluminescent displays. When disturbed or stimulated, the zooids can produce waves of blue-green light that travel along the length of the colony. This bioluminescence likely serves as a defense mechanism, startling potential predators or attracting larger predators to threaten whatever is attacking the pyrosome.

The 2017 Pacific Bloom Mystery

In 2017, scientists witnessed an unprecedented event off the coasts of Oregon and Washington. Massive numbers of pyrosomes appeared in Pacific waters, creating blooms so dense they clogged fishing nets and overwhelmed local fisheries across hundreds of miles of coastline. Some individual specimens measured over 60 feet long, rivaling the length of blue whales.

This bloom was unlike anything marine biologists had previously documented. The sudden appearance of such massive numbers remains partially unexplained, though scientists theorize that changing ocean conditions, including temperature fluctuations and nutrient availability, may have created ideal conditions for pyrosome reproduction and growth.

Reproduction and Growth

Pyrosomes reproduce through a complex process involving both sexual and asexual reproduction. A single fertilized zooid develops into a small colonial organism, which then grows by budding off genetically identical clones. This process allows pyrosome colonies to grow rapidly under favorable conditions, potentially reaching enormous sizes in relatively short periods.