I have well slacked off on this, but here is a hopeful return to the semi-regular feature of talking about plants and wildlife in the middle of the week! You can also see that I will be using my illustrations as well as my photographs to talk about each creature.
Many who live along the west coast of North America, from California to the central coast of British Columbia (and maybe even Alaska?), and who have been visiting the beach this spring, have encountered a surprise: thousands, perhaps millions of little blue creatures washed ashore and helpless. Some are about the size of a thumbnail, others are several inches across, but in these mass strandings they make quite an impression. So what are they?
Meet the Velella velella, also known as by-the-wind sailors or sail jellyfish. They are in the phylum cnidaria, which include jellyfish and other mainly aquatic animals, that use specialized cells (cnidocytes or nematocysts) for capturing prey – but velella are not jellyfish themselves. They are instead a siphonophore – a hydroid colony or community of polyps joining together to make what looks like one creature. The Portuguese man o’ war is another well-known siphonophore, and although they aren’t true jellyfish, I couldn’t resist featuring these two and another, the Porpita porpita, on my jellyfish poster.
These by-the-wind sailors are well named: they have a stiff “sail” on the top of their bodies that catches the wind to propel themselves across the sea surface. They are not capable of self-propulsion, leaving them at the mercy of the prevailing winds, which is why in some years (such as this one) they are washed ashore in mass strandings. Their sails are offset either to the left or the right, and so will disperse depending on the wind direction. The polyps and tentacles trailing below the float under the surface act as ballast to keep the velella upright.
Velella velella are carnivorous and catch plankton and other prey with trailing fishing tentacles covered in stinging nematocysts. The toxins in the nematocysts generally have little effect on humans, but nonetheless you should probably wash your hands after touching them when found on the beach. In turn, there are a few specialized nudibranchs (sea slugs) and marine snails that can prey on the velella and other cnidarians.
While the polyps comprising each velella velella are either all female or all male, they reproduce asexually, sending thousands of tiny (1mm) medusae out over several weeks. These medusae will then develop over a few weeks to spawn eggs and sperm which develop into plankton larva, which well then develop into a new velella colony.
Have you seen by-the-wind sailors either on the beach or out on the ocean? There are reports of them in the Atlantic ocean as well, mainly in temperate to tropical seas.