Atlantic Pyrosomes

• GeneralA floating colony of thousands of individuals that glows an intense blue when touched.
• Although it looks like a jellyfish, it is a tunicate — a distant relative of the vertebrates, and far closer to us than to the cnidarians.
• It makes daily vertical migrations of hundreds of metres, and its dense, fast-sinking faecal pellets carry carbon from the surface to the ocean floor.
• It is not one animal but a colony: thousands of individuals called zooids, each a few millimetres long, embedded in a common gelatinous tunic shaped like a hollow thimble open at one end.
• It propels itself collectively. Each zooid filters water and expels it into the inside of the tube, and the sum of all those jets drives the whole colony forward.
• It is intensely bioluminescent, hence its name, which means fire body. A flash in one zooid spreads through the whole colony in waves of blue-green light.
• It filters phytoplankton with extraordinary efficiency, and its dense, fast-sinking faecal pellets carry carbon to the seabed: they are a recognised component of the biological carbon pump.
• In 2017 there was a mass bloom off the west coast of North America that clogged fishing nets and covered beaches, a phenomenon without precedent in that area.

Habitat & environment

Ocean waters from 0 to 800 m

Sources consulted: Péron (1804); Sutherland et al. (2018), Journal of Plankton Research; Bowlby et al.