Cornwall's Recent Visitors: Atlantic Portuguese Man o' War

Over the past few weeks you may have noticed some funny (but quite cool looking) purple/blue sea creatures washed up on the shore or floating not too far out to sea around Cornwall. These organisms are an invertebrate known as Portuguese man o'war and - as much as they resemble them - they are not actually jellyfish as you may have thought. They are in fact "siphonophores", which are made up of a colony of genetically identical zooids; zooids all have different roles to play but work together as one functional unit/animal. There are four specific parts of a man o’ war which are responsible for different tasks, including reproduction and feeding.

So, what do you need to know?

Portuguese man-of-war can have tentacles up to 10m long that are covered in venom-filled nematocysts. These tentacles are used to paralyse their prey, usually consisting of fish and other small sea creatures. They will sting humans and, although a sting is rarely deadly, it will pack a punch and is reported to cause symptoms like those induced by an allergic reaction in some adults.

They don’t swim or have any means of propelling themselves through the sea, so they drift on currents or catch the wind and float in whatever direction it takes them. This is the main reason as to why we’re finding them cropping up around Cornwall this year. They are usually found in much warmer water and further out to sea but have been washing up on the south coast recently, primarily due to the recent extreme weather (e.g.hurricanes) and persistent winds coming in from the Atlantic. Really, they are just going with the flow! 

Some interesting facts:

- They usually float on the surface of the water, which means that they’re particularly vulnerable to predation. However, they’ve developed a clever way to avoid this! To avoid any threats, they possess air bags that they can deflate, allowing them to submerge themselves under water for a small amount of time and then pop back up when the threat has passed by.

- When there is particularly bad weather about, they don’t want their ‘sails’ and ‘floats’ that they use to move in the wind to be damaged, so they can deflate these to avoid any harm. These floats contain the rare gas Argon, but nobody knows why!

If you see any of these cool creatures around please make sure not to touch it. Make sure to let others around you - especially those with young children - avoid getting too close. However, also make sure to get a good photo of these amazing visitors while they're here visiting Cornwall on their travels!