It’s been rather windy of late. I don’t have the detailed information but I’m willing to bet that the western seaboard of the British Isles has been subjected to persistent, prevailing southwesterlies. One of my friends in conchology, David Fenwick, has been in touch with news of some of the pelagic animals which find their way onto the strandlines of our beaches from time to time.
Pelagic animals are those that live out their lives at the upper levels of the water column in oceanic waters. Often they float passively, driven by currents and climatic conditions. It needs a sustained interval of more or less unidirectional windy weather to wash these animals ashore.
David sent me news of a beaching of Velella velella. Velella is a genus of free-floating Hydrozoans that live on the surface of the open ocean, worldwide, and is commonly known by the names by-the-wind sailor, purple sail, little sail, or simply Velella. These little organisms, relatives of the more familiar jellyfish, are the food of Violet Sea Snails, Janthina janthina. The snails also feed on other oceanic drift animals such as the Portuguese Man o’ War and rely on passive encounters with their prey.
David found two Violet Sea Snails this week on the beach at Sennen Cove in Cornwall. They were still alive with their bubble rafts intact. There were also thousands of Velella. On taking the snails home and putting them in his tank, with some of their prey, they started to feed.
David sent me wonderful photos of the snails, which he generously allows me to reproduce here. In one you can just see the ringed skeletal structure of the Vellella as the snail feeds on it. Asked to confirm the snails’ identity, I was able to tell him these are the most common and the largest of the 4 species of Janthina.
David is a regular low-tider with an eye for noteworthy and unusual occurrences of the flora and fauna of the seashore and subtidal and he contributes information to the Marine Census of the Conchological Society. He illustrates many of his finds on his website Aphotomarine. Take a look at his other Janthina pictures.
Next time I will tell you why the snails float upside down, and how they build their rafts. I will also tell you about the Buoy Barnacle which David also found at Sennen.