The Marine Conservation Society (MCS) has released its annual Wildlife Sightings report to mark World Jellyfish Day, Friday 3 November.
The charity’s wildlife sightings project focuses on gathering reports of jellyfish and the marine turtles which feed upon them. The two animals are both vital in supporting ocean biodiversity and can be indicators of changes in the oceans, such as warming waters. The MCS report provides a detailed breakdown of the species observed, revealing the diversity of jellyfish in UK and Irish waters.
Jellyfish can be spotted year-round in the UK and Irish seas, but larger blooms are more likely to appear in spring, lasting through until autumn.
The 2023 report (covering 1 October 2022 to 30 September 2023) shows a 32 per cent increase in jellyfish sightings compared to the previous year. 75 per cent of the sightings were of individual jellyfish, while 11 per cent were of large blooms consisting of more than 100 individuals, an increase of 57 per cent from last year.
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Research has suggested that an increase in some jellyfish numbers around the UK could be related to climate change, however, there isn’t currently enough evidence of a direct causal link. In light of this, the MCS Wildlife Sightings programme aims to collect long-term data which can be used as a reference to study what jellyfish trends in UK and Irish waters might signify.
‘Jellyfish populations are highly variable year on year, and depend on several environmental factors that are different each year, such as sea temperatures and storms,’ said Dr Peter Richardson, Head of Ocean Recovery at the Marine Conservation Society. ‘Numbers of sightings we receive can also depend on the awareness of our sightings programme and the ‘wow factor’ of jellyfish people encounter.’
‘This year seems to have been a particularly good year for barrel jellyfish – one of our chunkiest jellyfish species that can occur in mind-boggling numbers when conditions are favourable. It’s only by observing trends over many years that we can start to suggest reasons for change.’
Barrel jellyfish accounted for 467 sightings, almost 27 per cent of the overall total, making them the most commonly sighted jellyfish of 2023 to date, and an increase of 21 per cent compared to the previous year’s results, when it was the sixth most-spotted species.
Barrel jellyfish – sometimes called ‘dustbin lid jellyfish’ due to their large size – can grow up to one metre in diameter. They have a solid, spherical, rubbery-looking bell which can be white, pale pink, blue or yellow. Rather than tentacles, barrel jellyfish have eight thick, frilled arms.
Crystal jellies, comb jellies, and the intriguingly-named ‘sea gooseberries’ made up 10 per cent of the total sightings this year, with crystal jellyfish the most reported ‘other’ species, accounting for 3.2 per cent of all sightings.
This year saw the charity’s volunteers submit reports of 12 marine turtle sightings, four of which were live leatherbacks. Six of the world’s seven marine turtle species have been spotted in UK and Irish seas, with the leatherback turtle most likely to be seen during the summer months, while stray juvenile loggerheads are sometimes encountered washed ashorein winter. Other species are occasionally swept into UK and Irish seas by strong winds and currents.
The Marine Conservation Society’s Turtle Code provides advice on what to do if a beached turtle is found, and all sightings are added to a national database.
‘The data on jellyfish and turtles that volunteers submit plays a vital role in understanding the changes occurring in our marine ecosystems, and help us to protect our seas,’ said Justine Millard, Head of Volunteering and Citizen Science at the Marine Conservation Society. ‘We urge anyone who has spotted a jellyfish or turtle to report it to us to continue to build a picture of our seas and the incredible life within them. A huge thanks to all the volunteers who have submitted data to us this past year.’
For more information on how to identify jellyfish and turtles, and to report a sighting, please visit the Marine Conservation Society’s website: at www.mcsuk.org/sightings