Taxonomy
- Kingdom: Animalia
- Phylum: Chordata
- Subphylum: Tunicata
- Class: Thaliacea
- Order: Pyrosomatida
- Family: Pyrosomatidae
- Genus: Pyrosoma
- Species: P. atlanticum (Péron, 1804)
General description
Pyrosoma atlanticum is a pelagic colonial tunicate belonging to the class Thaliacea. Colonies are cylindrical tubes that can reach up to 60 cm in length and 4–6 cm in diameter. The outer surface is gelatinous, dimpled with blunt backward‑pointing processes, and may appear pale pink, yellowish‑pink, or bluish. Each colony consists of numerous individual zooids (up to ~8.5 mm long) that are embedded within a rigid tube. Zooids possess a broad branchial sac with gill slits, an endostyle that produces mucus filters, and cilia that generate water flow through the colony.
Bioluminescence
P. atlanticum is capable of producing bright blue‑green light when mechanically stimulated. The bioluminescent response is generated by luminescent organs associated with each zooid’s inlet siphon. Current research suggests that the light may originate from symbiotic bacteria of the genus Photobacterium in the colony’s microbiome, although endogenous luciferase activity similar to that of Renilla species has also been reported.
Distribution and habitat
The species occurs worldwide in temperate oceans, typically between 50° N and 50° S. It is most abundant at depths below about 250 m but performs a pronounced diel vertical migration: colonies ascend toward the surface during evening hours and descend around dawn, with some large colonies moving vertically as much as 760 m each day.
Feeding ecology
P. atlanticum feeds on planktonic particles captured by mucus filters produced in the branchial sac. Studies indicate that it efficiently grazes particles larger than 10 µm, often outperforming other zooplankton grazers in particle capture efficiency. The colony’s movement through the water column facilitates encounter with food.
Reproduction and growth
Colony growth occurs by budding of new zooids around the periphery of the tube, lengthening the structure over time. No nervous connections link individual zooids; instead, coordinated responses (e.g., bioluminescent flashing) are mediated through light cues among neighboring zooids.
Associated fauna
Specimens of shrimp (Funchalia spp.) and various amphipods have been observed living within P. atlanticum colonies, indicating that the colonies can provide habitat for other marine organisms.
Research significance
Despite its wide distribution, P. atlanticum remains relatively understudied among planktonic grazers. Recent investigations into its microbiome and bioluminescent mechanisms aim to clarify the sources of light production and the ecological role of this species in marine food webs.