Seagrass Species Spotlight: Stalked Jellyfish
16 August 2022 / By Esther Farrant, Education Officer
It’s harvest season and our team of divers have been busy all over the southwest diving seagrass beds! From Osborne Bay in the Solent to the Helford River in Cornwall, and many favourable condition sites in between, the reproductive shoots containing precious seeds for cultivation are being harvested! An important part of our harvest efforts is to ensure that no wildlife is bagged up with the seeds. That is straightforward when it comes to giant spider crabs, or even well camouflaged pipefish and hermits, as our divers have keen eyes and attention to detail when checking each shoot. However, one member of the seagrass bed community that we need to be especially aware of is the stalked jellyfish.
The stalked jellyfish is a curious creature, a type of ‘staurozoan’ from the jellyfish family, it is about 2 centimetres in length can be found all around the British Isles. They tend to blend in with their surroundings, so often go unnoticed except to those who seek them out.
Stalked jellyfish differ from true jellyfish in a few ways, namely by being in one place for their entire adult lives. Larvae of stalked jellyfish will crawl along the seabed looking for a safe place where they will settle and change into an adult. Traditional bell-shaped floating jellyfish are planktonic and drift through the water column, but staurozoans live attached to seagrasses, kelps, rocks, or other hard surfaces in cold water around the coast of the UK, often found in shallow waters with good currents for bringing in tiny, planktonic food. Unlike its drifting cousins, the mature stalked jellyfish is completely sedentary, remaining stuck to the blades of seagrass or any other safe surface for the rest of their lives. They do, however, still have the same stinging tentacles, nematocysts, for which their mobile cousins are famous. Each of the stalked jellyfish’s eight arms has approximately 45 tentacles, the harpoon-like cells of the tentacles deliver a sharp sting to any prey which drift close enough, and stick tight, allowing food to be pulled into their mouth.
These funny sticky creatures can grow to a maximum length of around 4.5cm and vary in colour from shades of green, to reddish browns. The umbrella of stalks that give this jellyfish its name are covered in bright turquoise warty spots. These warts are storage vesicles and play a part in the defence mechanism of the jellyfish.
- Stalked Jelly fish have 360 stinging tentacles – 45 stinging on each of its eight arms!
- They are small but dangerous to others in its community, humans cannot feel it’s sting.
- Stalked Jelly fish are the laziest of jelly fish as they stay still for their entire adult lives.
- Stalked Jelly fish are masters of disguise, blending in seamlessly with their seagrassy home.