Autumn and winter storms often deliver strange oceanic creatures to our shores. Many have succumbed in the rampaging seas and whilst it can be sad to see the lifeless forms along the tide line it also affords the chance to see these otherwise alien species up close. By-the-wind-sailor (Velella velella) is one of these.
It’s a rather attractive hydroid colony (rather than a single animal). When alive they are a rich indigo grading to midnight blue. They are dainty, consisting of a coloured horizontal disk with small tentacles beneath it, and a vertical, ridged, transparent sail which helps propel them across the surface of the water. This is the polyp phase of the colonies life. Whilst they look ‘pretty’ they are carnivorous, catching plankton prey using their tentacles. Whilst we generally associate jellyfish stings as being painful, the toxins that By-the-wind-sailors produce are not normally harmful to humans, but effectively incapacitate their prey. The colony is networked by a series of canals which allow any food caught to be shared. Each colony is either all male or all female, and within it there are different types of polyps some of which can both feed and reproduce, whilst others are for protection.
As well as being predators they are also predated. Specialised sea snails such as the Violet Sea Snail (Janthina janthina), and various sea slugs will all predate By-the-winds-sailors. Its genus is made up of only one species found in all the world’s oceans, often in extreme abundance. In the last few week’s, large wrecks have been reported along some British beaches and the accompanying images were all taken on Islay, Argyll, a few days ago. If you have the chance to get out to the coast make sure you check the tide line carefully for these wind-blown oceanic waifs.