It has been another bumper year for jellyfish sightings in UK seas, according to the Marine Conservation Society (MCS).

The UK marine charity says the massive barrel jellyfish have appeared in record numbers for a second consecutive year, whilst in July huge numbers of mauve stingers were reported off Guernsey, and the potentially dangerous Portuguese Man O War has been washing up on beaches in the South West.

Portuguese Man O War. Credit: Peter Soper

MCS says that the rise of jellyfish in UK seas can no longer be ignored, and that more dedicated research and monitoring is needed to understand these apparent increases and what they mean for the state of our seas.

Dr Peter Richardson, MCS biodiversity and fisheries programme manager, said: ‘Our National Jellyfish Survey suggests significant recent rises in the numbers of some jellyfish species in UK seas, most notably the barrel. The million-dollar question is why is this happening? At the moment we just don’t know.’

The MCS Jellyfish Survey started in 2003 and involves thousands of sea and beach-going public reporting their jellyfish encounters online at the MCS website. 2013 was a record year, with the survey receiving over 1,000 reports involving hundreds of thousands of jellyfish.

Last year the number of reports increased again to over 1,400 reports, and by July this year the survey had already received over 1,000 reports. August is usually a peak month for jellyfish sightings and so 2015 looks set to be another record breaker.

Barrel jellyfish. Credit: Amy Martin

The charity says that barrel jellyfish normally make up 10% of its annual reports, but last year they made up 40%. So far in 2015, 75% of records have involved barrel jellyfish sightings.

Dr Richardson added: ‘We know that our seas are changing through climate change, resulting in rising sea temperatures and increased ocean acidification, and we know our seas are also heavily fished.

‘At the same time we seem to be witnessing increases in jellyfish around the UK. Is this an anomaly, a coincidence, or are the jellyfish telling us something about fundamental changes in the condition of our seas?’

Huge ‘smacks’ of jellyfish are not a new phenomenon, with jellyfish blooms having been found in the fossil record over 500 million years. Nowadays they can have important economic and social consequences.

Mauve stinger. Credit: Paul Naylor

Moon jellyfish blooms have forced the closure of UK nuclear power stations, leading to the industry investing in remote sensing mechanisms to detect increases in jellyfish near power plants. In the UK large blooms of mauve stinger jellyfish have wiped out salmon stocks in fish farms, while the same species regularly closes down bathing beaches in the Mediterranean due the animal’s painful sting.

Dr Richardson. said the MCS believes ‘there is now a need for UK Government to commission dedicated scientific research and monitoring to answer pressing questions about what is happening to jellyfish numbers, why it is happening and what this means for our precious and productive seas.’

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MCS urges the public to report their jellyfish sightings online at www.mcsuk.org, but urges caution, suggesting people look at, but don’t touch jellyfish because their stings can range from mild to very painful.