In recent weeks there were several reports of large numbers of Velella velella floating close to the shore in several parts of Malta and Gozo.
I also read about large numbers invading the sea in southern Italy. I had been seeing small numbers of these interesting hydrozoans since late winter but a few days ago I was amazed to see tens of thousands floating at the Blue Lagoon in Comino.
Velella velella is a scientific name. The species is commonly known as by-the-wind-sailor or velella which is the name I prefer. It is also known as sea raft, purple sail or little sail.
The velella is found in all warm and temperate waters of all oceans. The organism is like an oval, translucent, deep-blue plastic with a transparent sail on top.
It lives on the water surface and is at the mercy of the wind, tides and currents for transport. It is often found in large numbers and sometimes hundreds of thousands are stranded along the coast.
Each individual velella is a colony of hydrozoans. It is made up of specialised polyps attached to a floating structure. The various polyps in the colony have different structures and responsibilities, including feeding and reproduction.
The velella is carnivorous. It feeds on small plankton which it catches by means of stings found on the tentacles of some of its polyps. These stings are strong enough to immobilise very small creatures but have no effect on man, so are totally harmless.
The velella is preyed upon by a number of predators including a purple snail, which has a very thin delicate shell and floats by anchoring itself to a raft consisting of small air bubbles.
Very often, purple snails are stranded together with the velella.
I got to know about the velella about 15 years ago when I photographed it in St Julian’s Bay. I do not recall having ever seen it before then and I had spoken to many people about it to find out whether they were familiar with this species.
Many seemed to be unaware of its existence.
Since then, it seems to have become more common and nowadays I see it in large numbers nearly every year.
The increase in numbers of velella seems to follow the increase in the number of jellyfish to which the velella is related.