Species of the week- 17

The species I’ve chosen this week is something completely different to anything I’ve written about before, it’s Velella velella, otherwise known as the By-the-wind-sailor. It is in the phylum Cnidaria, (along with jellyfish and anemones), but is itself a colonial hydrozoan. This means that each By-the-wind-sailor is actually composed of many small organisms, some of which are specialised to feed and reproduce, others of which are specialised for protection. Though there are other colonial hydrozoans, the By-the-wind-sailor is unique enough to be the only member of its genus globally. Here is one of many By-the-wind-sailors which were washed up in the Penzance area following recent high winds.


Velella velella


Velella velella is unusual in that the colony has no control over where they are travelling, their direction of travel changes with the wind, which blows their sail-like structure. Some By-the-wind-sailors have their sail running diagonally across the ‘float’ from NE to SW, whereas others have their sail NW to SE. This means that under the same wind conditions, different individuals may drift in completely opposite directions! At first this might seem counterintuitive, but I believe (I haven’t done my research into this) that it’s a very clever adaptation. Relying purely on the wind as a form of locomotion is risky, and can cause mass strandings of V.velella. By having two forms which travel in opposite directions in the same wind conditions, it is ensured that whilst some individuals are blown towards land, others will be blown away. That’s my idea anyway…

V.velella can be found in all of the worlds oceans, but is rarely seen close to land. It feeds on whatever small organisms get caught by its dangling tentacles, which can include shrimps and young fish. In the UK, this unmistakeable species is rarely recorded away from the far Western coasts, nearest to the Atlantic Ocean. Here is its distribution:


The recent strong Westerlies have caused many NE to SW sailed By-the-wind-sailors to wash up on the Cornish coasts. These individuals will have been blown North-west from the central Atlantic Ocean. The strong westerlies haven’t just been bringing Velella velella to our shores, but rare birds too! Today, a cracking 1st winter Bonaparte’s Gull (from North America) turned up at Helston boating lake, and an American Herring Gull was reported further West! I suspect flocks a Ring-billed Gulls to be reported over the coming days. It could be a good week of birding… Here are a couple of phonescopes of the Bonaparte’s Gull from earlier (off-topic but it’s a beauty).




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