An unusually high number of jellyfish have arrived in UK seas this summer, with marine experts linking the phenomenon to record-breaking sea surface temperatures and the broader impacts of climate change on marine ecosystems.
The Marine Conservation Society recorded 1,432 jellyfish sightings in 2024, representing a 32% increase compared with the previous year, as warm water conditions create optimal breeding environments for multiple species.
Climate-driven marine changes
Jellyfish blooms arrive annually for their reproduction cycle by following warm water currents to coastal areas. However, this year’s conditions have been particularly favorable due to record-high sea surface temperatures in April and May, according to Met Office data.
Abigail McQuatters-Gollop, a marine conservation specialist at the University of Plymouth, explained that warm sea surface temperatures, which are exacerbated by global heating, create favourable conditions for jellyfish. This contributes to population blooms and extended summer residency periods.
The warming trend is also expected to facilitate the arrival of new jellyfish species that prefer warmer waters, potentially altering the composition of marine ecosystems around UK coasts.
Species diversity and ecological role
Multiple jellyfish species have been identified in UK waters this year, including moon, lion’s mane, blue and mauve stinger varieties. However, two species have garnered particular attention from marine biologists.
The compass jellyfish, characterised by dark stripes on their bells and long tentacles that deliver painful stings, serves as a particular favourite source of food for turtles, according to McQuatters-Gollop.
A common but spectacular species arriving in great numbers is the barrel jellyfish, which can grow to a meter in diameter and features a thick bell with frilly arms. This species delivers a relatively mild sting and is consumed by humans in parts of Asia.
Foundational marine ecosystem function
Jellyfish play a critical role in marine food webs as types of plankton that form the foundation of many oceanic food chains. Their presence supports various marine species, from small fish to large marine mammals, highlighting their importance beyond their often-feared reputation among beachgoers.
McQuatters-Gollop emphasised the ecological significance, noting that jellyfish are foundational elements of the aquatic food web, supporting broader marine biodiversity.
Climate change implications
The increase in jellyfish populations reflects broader climate-related changes in marine environments. McQuatters-Gollop stated that evidence suggests we are “more likely to have more jellyfish blooms because of climate change and the water getting warmer.”
The warming waters create a complex environmental dynamic, as while jellyfish benefit from higher temperatures, they remain vulnerable to extreme weather conditions. Composed of 90% water, jellyfish are susceptible to strong currents and can break apart easily, with extreme weather conditions representing another effect of climate breakdown.
Seasonal lifecycle patterns
Despite the current abundance, the jellyfish presence will be temporary due to their short lifespans, with some species being born and dying within the same summer season. After summer concludes, McQuatters-Gollop explained that some jellyfish may follow the current back out to sea, while others may “live out their days in the UK and die when they use up all their food supply, break apart from a storm, or from old age after they reproduce”.
Conservation and public engagement
Marine experts are encouraging public appreciation of these marine creatures while emphasising safety. McQuatters-Gollop described jellyfish as having beautiful colours, long tentacles streaming behind them, and looking “like something that belong in outer space”.
She advocated for public engagement, stating: “I wanted to encourage people to safely observe jellyfish and fall in love with them, because they are amazing and I feel so lucky when I dive and swim alongside them.”
Future monitoring and research
The significant increase in jellyfish sightings provides valuable data for marine scientists studying climate change impacts on marine ecosystems. The Marine Conservation Society’s monitoring program continues to track these population changes, contributing to broader understanding of how warming seas affect marine biodiversity.
The jellyfish boom serves as a visible indicator of changing ocean conditions, offering researchers insights into how marine ecosystems are adapting to climate change while highlighting the interconnected nature of ocean warming and marine life distribution patterns.
Public safety considerations
While celebrating the ecological significance of jellyfish, marine experts emphasise the importance of safe observation practices. Many species deliver painful stings, and beachgoers are advised to observe jellyfish from a distance and avoid direct contact, even with specimens that appear inactive on beaches.
The current abundance provides an exceptional opportunity for public education about marine ecosystems and climate change impacts, though safety remains paramount during any jellyfish encounters.