A small natural sailboat
The velella is an open-ocean organism that is part of the pleuston, i.e. a species that lives on the surface, at the water-air interface.
Rather pleasing to the eye, this cousin of the jellyfish moves with the wind and currents. Their translucent sail and blue float are reminiscent of a small sailing boat, and give them great mobility.
Nicknamed saint Peter's boat by Provençal sailors, their waterline length doesn't exceed 6 cm, while their air draught is limited to 3 cm.
The sail plan is triangular or semicircular, and balance during navigation is ensured by multiple polyps and tentacles that ballast the boat.
A non-invasive species
It is most frequently encountered on the Mediterranean coast, although its presence has been reported all along the French coast, in the West Indies, in North America and in the Indo-Pacific zone. Often in spring, purple tides come ashore, never to leave. It takes a few weeks before they disappear completely.
It feeds on zooplankton, which is caught by the tentacles on its belly. It is little hunted by fish, apart from the sunfish, its main predator.
A very low risk for humans
Although its affiliation with the jellyfish family naturally puts humans off, the vellèle poses few risks. Unlike many of its cousins, it stings very little when stranded. On the other hand, if you come across one off the coast while swimming, you may feel a slight discomfort on contact, but nothing dramatic.
Its main shortcoming is revealed after a massive stranding, when its decomposition gives off a disgusting odor akin to rotting fish.
If you come across one on the beach or in the rocks, don't put it back in the water if you hope to see it sail, as a simple grounding is fatal.
