The climate crisis brings a growing number of unusual jellyfish to UK seas

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<p><figcaption class=Photograph: Cornwall Wildlife Trust / PA

According to a survey by the Marine Conservation Society (MCS), Britain’s seas are becoming populated with large groups of unusual jellyfish due to climate collapse.

In its first marine sighting report, which is based on 20 years of citizen science, society found a greater abundance of types of jellyfish, including those normally found in warmer climates. Thousands of volunteers take part in the MCS report, telling the conservation team which species of jellyfish and turtles they have seen.

A total of 1,315 sightings of jellyfish were reported to the MCS between 1 October 2021 and 30 September 2022. Eight species of jellyfish are normally sighted in the UK and Ireland, but 11 have been spotted this year, with rarer visitors now visiting these waters

Bioluminescent crystal jellyfish made up 3% of total sightings – these animals are almost completely transparent, but emit stunning blue-green light under certain circumstances due to the fluorescent protein their bodies produce. They are usually found in the Pacific Ocean and rarely visit UK waters. One percent of the sightings were sea gooseberries. Both were the highest percentages reported to date. The new arrivals suggest warmer temperatures could affect jellyfish diversity in the UK.

Last year, there was an increase in sightings of the infamous Portuguese man o’war, a jellyfish-like creature that can deliver a stinger powerful enough to kill a human. Those increased by 2% from the previous year. The charity reported an increase in “other” species seen, from 5% to 9% this year.

It is thought that the increase in the number of jellyfish species and their abundance could continue due to the climatic collapse.

Amy Pilsbury, citizen science project manager at MCS, said: “Changes in the abundance of jellyfish can be influenced by many different factors of climate change, such as sea surface temperature, salinity, pH, oxygen availability and habitat changes. Future climates will further change marine dynamics and continue to influence planktonic communities ”.

Unlike many other marine creatures, jellyfish are very suitable for living in difficult environmental conditions.

Pilsbury added: “Jellyfish are highly resilient and adaptable to changing environmental conditions. This sometimes results in large jellyfish blooms of hundreds or even thousands of individuals. These can disrupt marine ecosystems and be extremely damaging to human activities.

“The Marine Conservation Society’s nearly 20-year dataset, collected by citizen scientists, can be used alongside climate data to investigate how changes in our ocean are affecting our ocean visitors.”

Pilsbury explained: “The data show an upward trend in some species sighted on our shores over the past 20 years, such as the Portuguese man o’war, for example. Preferring to drift offshore, they run the risk of being washed ashore by strong winds and storms, which are becoming more frequent in the UK. Other reports show a slight downward trend over time, such as the moon and lion’s mane jellyfish, which could indicate changes in plankton communities as sea temperatures rise. “

Sea turtles sometimes benefit from a boom in the number of jellyfish. Reptiles visit UK waters in the summer months to feed on them. Last year, MCS volunteers reported 11 turtles, six of which were live leatherback turtles, sighted on the coast of Scotland.

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