Jellyfish strandings in Swansea Bay
Unusually large numbers of jellyfish have been reported on the West Wales coast in recent months. Swansea News Network was recently contacted by Botond Vasarhely who kindly offered to share his photographs of one very spectacular jellyfish he spotted whilst out walking on the beach at Blackpill. Botond was visiting Swansea in the lead up to the Spring Bank Holiday and was surprised to see the large jelly-like bell-shaped mass of the adult, also known as a medusa, stranded on the beach. The species was later identified as a Barrel Jellyfish, Rhizostema octopus . Swansea News Network wanted to find out more about just why there have been so many of these particular creatures appearing in the bay area.
Jellyfish are related to sea anemones and corals. According to the Marine Conservation Society, a good number of Barrel Jellyfish have been spotted in South West Wales recently. These fascinating jellyfish grow to as big as 90cm wide and can weigh as much as 35kg. The Marine Conservation Society rather handy Jellyfish Survey guide describes these as “Robust with a spherical, solid rubbery bell which can be white or pale pink, blue or yellow and fringed with purple markings. The bell lacks tentacles but eight thick, frilled arms hang from the manubrium. It has a mild sting. ” Jellyfish are quite complex. The manubrium is apparently the mouth (which also acts as an anus) and arms, underside, and centre of the bell.
Richard Harrington from the Marine Conservation Society said;
You can’t say Barrel Jellyfish are harmless as they do have stinging cells just like other jellyfish. But, by and large, you are unlikely to be stung and it would only normally feel as mild as being stung with a stinging nettle.”
The Marine Conservation Society’s advice if you suspect you have been stung by jellyfish is;
You should seek medical advice. Some stings are calmed by acids and others by alkalis so it is important to know the species.”
It’s probably also worth noting what the jellyfish looks like and to take a picture if that is at all possible to help with identification.
Key advice from the Marine Conservation Society is;
While some jellyfish are harmless or have a mild sting, others have a painful or dangerous sting. MCS would therefore recommend that, for your own safety, you do not touch jellyfish.”
Stranded jellyfish often succumb to drying out in the sun but this paryicular species can be remarkably tenacious of life and can survive to be occasionally washed back alive into the sea again at the next tide.
I asked Richard Harrington if climate change may be having an effect on numbers in recent years.
We cannot say the increase is categorically linked to climate change. There have been more anecdotes of Barrel Jellyfish in spring, but our surveying has only been running for over a decade now, so it is impossible to form an opinion just yet.”
The Marine Conservation Society are keen to hear about your sightings of jellyfish to help their work. Jellyfish are a staple food of endangered Leatherback Turtles and the largely tropical water and strange looking Giant Sunfish, Mola mola, (now increasingly found in waters off western U.K. coasts). Knowing jellyfish numbers and their distribution helps in the research to protect the vulnerable species.
The public is encouraged to report sightings of stranded jellyfish to the MCS jellyfish survey. For those volunteers who are happy reporting strandings, it’s worth remembering the Marine Conservation Society are also pleased to hear when no jellyfish are spotted to help complete their statistical picture of population numbers and distribution patterns.
It seems the recent proliferation of jellyfish, known as blooms are triggered by a number of environmental factors. This includes a rise in sea temperature but also according to Richard Harrington the proliferation can be influenced by more abundant nutrient supply and other factors. So the reason for the recent rises in numbers is open to speculation and are not dependent on the sea simply getting warmer.
9 facts you might like to know about jellyfish
Jellyfish range in size from less than 2 and a half centimetres long to 214 cm long, with tentacles 30 and a half metres long.
The main body or medusa (medusae, plural), is named after Medusa the female winged creature of Greek mythology who is generally described as having living venomous snakes in place of her hair. Those who gazed at her face would be turned to stone.
Jellyfish don’t have bones, a brain or a heart. They have rudimentary sensory nerves at the base of their tentacles with which they can orientate themselves, detect smells and sense light.
Jellyfish are made up of about 98% water.
Jellyfish have radial symmetry meaning their body parts extend outwards from a central point (something like the spokes of a wheel).
The adults or medusae may only live between 3 and 6 months. Barrel jellyfish can survive near the surface of the water through the cold winter.
A jellyfish’s main food source is plankton. Plankton are the diverse range of organisms (plants, animals, and others) dominating the surface layers of the oceans. They live in the water and are unable to swim against the current.
The most common jellyfish in Welsh waters is the Moon Jellyfish, Aurelia aurita , which grows up to 40cm in diameter, is transparent with short hair like tentacles and 4 distinct pale purple rings in the bell and has just a mild sting.
Jellyfish can be transparent or have striking colours. Some get their nutrition in a symbiotic relationship with zooxanthellae; photosynthetic organisms that contain chlorophyll and other colourful substances that show up in the brightly coloured medusa body. In the daytime, the organism provides the jellyfish with organic carbon products giving as much as 90% of the jellyfish’s energy needs for growth etc. In return, the zooxanthellae get nutrients, carbon dioxide and a lift up to the brighter light of the surface waters lit by the warmth of the sun.
Where do jellyfish come from?
Jellyfish have a complex life cycle made up of both sexual and asexual (non-sexual stages). The male adult medusae release their sperm into the water and these swim to a female to fertilise her eggs. These hatch as a mobile planula or larval stage. The planula hooks onto rocks and grows into another stage known as a polyp, which are simple cylindrical shapes with tentacles and a mouth at the top looking not unlike sea anemones. These polyps can survive months or years and bud (known as strobilate, to another stage called an ephyra. This is the form that grows into an adult medusa. It is the budding that can lead to large numbers or blooms of jellyfish that can often be seen in the summer months around the Welsh coast.
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