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  • Writer's pictureBeth Matlock

Swim a mile in their seas

So, I had an idea to start a series following a different marine species every week and explain the different adaptations they have developed to allow them to thrive in their environment. Much like 'walking a mile in their shoes' I hope to highlight the sometimes intense and harsh conditions some species have had to adapt to in order to survive.

This week I want to focus on what is commonly known as the 'immortal jellyfish' (Turritopsis dohrnii). The 'head of the jellyfish, known as the bell, can reach a diameter of 4.5 millimetres and is as tall as it is wide. One distinguishing feature of this jellyfish is that the stomach is bright red. Juvenile jellies usually 1mm in size can have only 8 tentacles, however, when they reach adulthood the number of tentacles rises to between 80 and 90. This particular jellyfish is commonly found in the pacific but has spread all around the world, due to this global migration they have also managed to create several distinct populations through speciation (forming new species through evolution). Usually, the fact that jellyfish have multiplied and spread around the world would cause issues for humans and other species, however, due to their size their spread went largely unnoticed.

I know what you are thinking..Yes they look cool but what makes them special? Well this is where things get interesting...

There is a reason these jellyfish are known as the 'immortal jellyfish' and here is why. For the vast majority of species on Earth they have a fixed lifespan, meaning they are born and then grown up and eventually die. This however is not the case for the Turritopsis dohrnii. This species of jellyfish is only form that is known to have developed the ability to transform back into a polyp (formed from larvae and is attached to the sea floor - jellyfish bud off polyps and begin their free-swimming form). This change can only happen in the presence of certain cell types that the Turritopsis dohrnii holds.

This transformation occurs when there are conditions in its life cycle that are challenging or not optimal for its existence. For example, conditions of starvation, reduction in the salinity of the water or a sudden change in temperature. By changing back into polyps, this protects them from adverse conditions that may prevent them from surviving. This process allows them to avoid death and continue their life cycle and also protect them species from dying out. Naturally, some dangers such as predation are inevitable. However, being able to revert back to its original form, especially with global warming and other factors affecting our oceans this could help this particular species survive. Scientists have been studying the 'immortal jellyfish' as they believe it may hold answers for renewing damaged or dead tissues in humans.

I personally feel the Turritopsis dohrnii has earnt a place on my list of species with extraordinary adaptations. I know I would love the chance to revert back to a younger version of myself as I'm sure many of you would too.

I will be covering another amazing marine organism next week and I hope you have enjoyed learning about one of the many bizarre and crazy species in our marine world!

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