Sunday, December 7, 2014

Floating Sails

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 this interesting hydrozoan 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. It is commonly known as by-the-wind-sailor or velella which is the name I prefer. The velella is also known as sea raft, by-the-wind sailor, purple sail or little sail.

The velella is found in all warm and temperature waters of all the 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 become 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 responsabilities 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 this species is does not sting and is totally harmless. 

The velella is preyed upon by a number of predators including a purple snail. This snail 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 fifteen years ago when I photographed it in St Julians 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 I first saw it, 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 number of jellyfish to which the velella is related. 

This article was published in The Times of Malta on 15 May 2014. 

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