Monday 10 April 2023

Thousands of By-the-wind Sailors wash up on Californian beaches.

Beachgoers in California are reporting thousands of By-the-wind Sailors, Velella velella, small colonial Hydrozoans distantly related to the Portuguese Man o' War, Physalia physalis, washed up on the beaches between Dana Point in Orange County and Point Reyes National Seashore, to the north of San Francisco. Mass strandings of By-the-wind Sailors are not unusual in spring and summer in California, particularly when there are strong onshore winds, as has been the case recently. It has been suggested that such mass strandings may be an early warning of a developing El Niño weather system over the Pacific, something predicted for this year.

A mass stranding of By-the-wind Sailors, Velella velella, on a beach at the Point Reyes National Seashore. Point Reyes National Seashore.

While these brightly coloured and superficially Jellyfish-like animals can be alarming, they are considerably less dangerous than the Portuguese Man o' War, as their toxin is not particularly harmful to Humans, though it is worth avoiding handling them, as they can cause itching and some people may have an allergy to the sting.

Like the Portuguese Man o' War, By-the-wind-sailors are colonial Siphonophores only distantly related to true Jellyfish, Scyphozoa, though commonly referred to as such. Their bodies are made up of thousands of individual zooids, each with their own sting, tentacles and digestive system. New zooids are formed by budding from other members of the colony, but remain attached to these to form a single colony. These animals are anchored to the sea surface by a highly modified zooid which forms an air sack, filled with a mixture of carbon monoxide defused from the zooid and nitrogen, oxygen and argon from the atmosphere, which are brought into the sack through osmosis. 

The anatomy of the By-the-wind-sailor, Velella velellaTBR's Muscles.

However they are rather smaller, with colonies seldom exceeding 7 cm in length, and differ somewhat in their reproductive cycle, with alternative generations of sexual colonies, which may be male or female and reproduce sexually, budding off asexual stages medusae, which are about a mm across, and produce eggs which can go on to form new colonies.

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