Species Focus - Hydrozoans

Many of us will soon be inviting or visiting relatives for various celebrations coming up. At this time of year we also experience our warmest seas with warmer currents coming into our western coasts. These bring less commonly seen species such as the relatives of our jellyfish species.

These hydrozoans are colonial animals, living and working together as they travel the seas. They can be found occasionally in small numbers, sometimes in much larger groups, washing up on shore and creating a more colourful strandline with their purples and blues.

The Portuguese Man O’War (Physalia physalis being one species) looks more like a jelly but their inflated float sits on the surface, unlike those of jellies. The animals (polyps) live below the float, all with different tasks, while the fishing polyps form the stinging tentacles below that; sitting in the water, catching prey. Ocean wanderers, they move with warm currents and are rare but regular visitors to our shores, perhaps more so these days than previously.

By-the-Wind Sailors (Velella velella) have a similar setup to the previous species but are smaller and much more compact. Their float is less globular and designed with a horizontal platform and a “sail” sticking up. Interestingly, if just their existence isn’t enough on its own, these can have left-handed and right-handed sails, likely to help with dispersal, utilising the wind in different ways. Being much smaller in size, they can be a tricker find on shore. When they’re freshly washed up, however, they’re still their vibrant, deep colour and in some years they can be washed up en masse, turning the beach a rich blue!

These species are a food source for a particular mollusc which travels with them, forming its own float by producing bubbles which sit on the water surface. The Violet Sea Snail (Janthina janthina) is seen even less commonly, but well worth keeping an eye out for when the word is out that we have a visit from its prey. Take care of yourselves and dogs, though. The Portuguese Man O’War can continue to sting when dead.These species are a food source for a particular mollusc which travels with them, forming its own float by producing bubbles which sit on the water surface. The Violet Sea Snail (Janthina janthina) is seen even less commonly, but well worth keeping an eye out for when the word is out that we have a visit from its prey. Take care of yourselves and dogs, though. The Portuguese Man O’War can continue to sting when dead.

All these can be recorded, together with other strandline finds by way of the Beached! project.