Increased portuguese man o’war sightings

August 30th, 2008

There have been increased reports of Physalia physalis sightings over June, July and August. Physalia physalis or the Portuguese man o’war consists of a large gas-filled float (pheumatophore) which reaches 300mm in length and 100mm in width. Physalia physalis is light blue/purple in colour and has a bright pink crest running along the top of the float or pheumatophore that acts as a sail. Physalia physalis has polyps under the pheumatophore for feeding, defence and reproduction that are several metres in length. Physalia physalis are carnivorous and feed on small crustaceans and larval fish primarily. They do this by delivering an immobilising sting to their prey with tentacles covered in nematocysts or stinging cells. The sting of Physalia physalis is potent, even after death.

Photo: Steve Trewhella

There have also been reports of sightings of Pelgia noctiluca and Buoy Barnacles in Dorset.

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Jellyfish in November

November 19th, 2007

This month, there have been a number of jellyfish sightings including the String Jellyfish in Cornwall and the Mauve Stinger in the North Channel.

The String Jellyfish Apolemia uvaria, is not actually a jellyfish but belongs to a related group Siphonophora and is related to the Portuguese Man o’ War. They were reported in large numbers and have been spotted off Plymouth sound in the last 4-5 weeks. These unusual creatures have not been recorded in Plymouth or Cornwall before. They are usually found in oceanic waters and have a nasty sting.

Recently, there have been several sightings recorded in the North Channel, North West Ireland and Western Scotland of the jellyfish Pelagia noctiluca, more commonly known as the mauve stinger.

Photo: Steve Trewhella

The mauve stinger can grow up to 10cm in diameter; its tentacles can extend up to 3m and are covered in nematocysts. Its colour varies from mauve-brown to purple and pale red and the exumbrella or the outer surface of the mushroom-shaped bell is covered in nematocyst-bearing warts, pink or mauve in colour. Nematocysts, also called stinging cells, contain small poisoned tubes that deliver its sting. Pelagia noctiluca usually feed on sea squirts and other small jellyfish.

These species also have a nasty sting so approach with care!

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Violet sea snails found in Ireland

September 15th, 2007

In August and September, there have been several reports of violet sea snails sighted in Ireland. The violet sea snails, Janthina pallida were discovered on a strand in County Sligo and Janthina pallida and Velella velella were both found on Portnoo beach in Donegal.

A mass stranding (>200) of violet sea snails (Janthina pallida) was discovered in County Sligo. These snails grow to about 25mm high and spend their adult life floating on the surface of the sea. This is achieved by creating a ‘raft’ of air bubbles that is encased in a thin layer of chitin produced by the foot. They are often washed ashore during storms and they feed primarily on the siphonophore, Velella.

In Donegal, both Janthina pallida, some of which had bubble floats with eggs attached, and the purple sails, Velella velella, were found washed up on the beach. These organisms usually live on the open sea but can become stranded on beaches if the prevailing winds drive them onto the shore. Velella velella, also known as ‘Jack Sail by-the-Wind’, is deep blue to blue/violet in colour. They are about 100mm in length and are eaten by the violet sea snails, Janthina. Velella velella feeds on young fish, crustaceans and other organisms caught by the nematocysts (stinging cells) on the tentacles.

Photo: Steve Trewhella

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