Bright blue, orange, and pink jellyfish have been spotted all over the UK last year and documented by the Marine Conservation Society (MCS).

According to data gathered by the MCS, the number of jellyfish sightings on the UK coastlines increased by 32%.

Barrel jellyfish were the most frequently observed, accounting for 437 out of 1,737 sightings between October 1, 2022, and September 30, 2023.

Barrel jellyfish are sometimes referred to as "dustbin lid jellyfish" because they can grow up to one meter in diameter.

Representatives of the public who collect data for the study also noticed several lion's mane jellyfish, blue jellyfish, and Portuguese man o' war.

The jellyfish population varies each year depending on environmental changes such as sea temperature and storms, but they typically thrive between spring and autumn.

June was the hottest month on record in the UK and brought a marine heatwave that raised sea temperatures by around 4°C.

The number of jellyfish reported to the MCS also depends on the "wow factor" of the jellyfish people encounter, said Dr. Peter Richardson, head of ocean recovery organization.

"This year seems to have been particularly good for barrel jellyfish - one of the largest species of jellyfish that we see in astounding numbers under the right conditions," he said.

"Only by monitoring trends over many years can we begin to suggest the causes of change."

Jellyfish are considered indicator species, signaling changes in the ocean, such as warming waters over time.

"Research has shown that an increase in some jellyfish numbers in the UK may be related to climate change, but currently, there is insufficient evidence to establish this link," said MCS.

Its "Wildlife Watch" program, the annual results of which were published today, collects long-term data to provide a benchmark for jellyfish trends in UK waters.