The Marine Conservation Society has released its annual Wildlife Sightings report, marking World Jellyfish Day on Friday 3^rd November.

The charity’s wildlife sightings project focusses on gathering reports of jellyfish and marine turtles, which feed on jellyfish. These two marine animals are both vital in supporting ocean biodiversity and are indicators of changes in our ocean over time, like warming waters. The charity’s report provides a detailed breakdown of the species observed, revealing the diversity of jellyfish in UK and Irish waters.

This year’s report (covering 1st October 2022 to 30th September 2023) shows a 32% increase in jellyfish sightings compared to the previous year.

Jellyfish can be spotted year-round in UK and Irish seas, but larger blooms are more likely to appear in spring, lasting through until autumn. The Marine Conservation Society’s report shows 75% of sightings were of individuals (1-20), whilst 11% of sightings were of large blooms of over 100 individuals, an increase of 57% from last year.

Research has suggested that an increase in some jellyfish numbers around UK could be related to climate change, however, currently there isn’t enough evidence to make this link. The Marine Conservation Society’s Wildlife Sightings programme aims to collect long term data which can be used as a reference to study the reality of jellyfish trends in UK waters.

Dr Peter Richardson, Head of Ocean Recovery at the Marine Conservation Society, said, “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. 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.”

The most frequently reported species during the reporting period was the barrel jellyfish, which accounted for almost 27% of total sightings (467). This is an increase of 21% compared to the previous year’s results, when it was the sixth most-spotted species. Barrel jellyfish are sometimes called ‘dustbin lid jellyfish’ due to their large size – they 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.

The report features other intriguing jellyfish-like species, including crystal and comb jellies, and sea gooseberries, which made up 10% of the total sightings this year. Crystal jellyfish were the most reported ‘other’ species, accounting for 3.2% of all sightings.

The Marine Conservation Society also records reports of marine turtles, which feed on jellyfish. The charity’s volunteers submitted 12 reports of marine turtle sightings this year, four of which were live leatherbacks. Turtle sightings contribute to a national database.

Six of the world’s seven marine turtle species have been spotted in UK and Irish seas. The leatherback turtle is most likely to be spotted feeding on our jellyfish during the summer months., while stray juvenile loggerheads are usually encountered washed up in winter. The leatherback, which is the largest sea turtle, and loggerheads are considered to be of ‘vulnerable’ conservation status. Reporting sightings of these incredible creatures will support the Marine Conservation Society and others in understanding their movements, potential threats and how better to protect them through policies and conservation strategies.

Other turtle species are swept into UK and Irish seas by strong winds and currents, though more suited to warmer waters. The charity’s Turtle Code provides advice on what to do if a beached turtle is found.

Justine Millard, Head of Volunteering and Citizen Science at the Marine Conservation Society, said, “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. 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.”

The Marine Conservation Society uses wildlife sightings by citizen scientists to:

1. Discover how jellyfish and turtle populations are changing around the UK – specifically when and where they are occurring each year
2. Investigate trends in turtle sightings to find out more about how they use our waters
3. Explore whether jellyfish distribution can tell us more about where leatherback turtle feeding grounds may be

For more information on how to identify jellyfish and turtles, and to report a sighting, please visit the Marine Conservation Society’s website: www.mcsuk.org/sightings.