Species: P. atlanticum
Pyrosomes are hollow tubular colonies of individual zooids that reside next to one another in a common tunic and result from asexual reproduction. Pyrosomes often produce light (bioluminescence) and are capable of forming dense aggregations. Tunicates come in two main varieties, solitary and colonial. Solitary tunicates often look superficially like sponges, and grows up to 600mm and are sometimes known as sea squirts. Each solitary tunicate represents an individual animal. Colonial tunicates (including pyrosomes), on the other hand, are communities in aggregate. Each colony comprises hundreds to thousands of cloned individuals known as zooids. A colony with tough consistency and cylindrical in shape, one end open and one end closed. It narrows toward the closed end and can be pink or yellowish pink in color.
Pyrosomes swim and feed by siphoning water through their tube using tiny hair-like projections, called cilia. It mainly feeds on plankton (centric diatoms, silico-flagellates and even fragments of small crustaceans, coccolithophores). By beating their cilia in concert, the entire colony helps to draw in seawater, which is sieved by a mucus filter to capture plankton for consumption. This concerted effort creates a constant flow of water through the tube, which powers the colony’s locomotion through the depths. Like many pelagic organisms, pyrosomes migrate vertically in the water column—they tend to congregate near the surface at night to feed, and retreat to the depths during the day. Large colonies have been known to cover a vertical distance of 2,500 feet daily during their migrations.
The gelatinous yet rigid tube these pyrosomes construct for themselves can reach two feet in length, but most of the specimens that washed ashore in Oregon this winter were much smaller. When alive, the colonies can actually glow—that is, the individual zooids are bioluminescent. The reason for this isn’t clear, but it’s possible the glow helps to attract plankton that pyrosomes feed on at night. The genus name of these animals translates to “fire body” in Greek, a nod to their luminescence.
Habitat and Distribution
P.atlanticumis found in temperate waters in all the world’s oceans, usually between 50°N and 50°S. It is most plentiful at depths below 250 m (800 ft).Colonies are pelagic and move through the water column. They undergo a large diurnal migration, rising toward the surface in the evening and descending around dawn. Large colonies may rise through a vertical distance of 760 m (2,500 ft) daily, and even small colonies a few millimetres long can cover vertical distances of 90 m (300 ft).