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Resorts along Spain’s Costa Brava are facing a significant increase in jellyfish populations, a trend linked to rising sea temperatures that have spurred their reproduction and migration northward.
Between May and August, nearly 7,500 people on the Catalan coast sought medical treatment for jellyfish stings - a 41 per cent increase compared to the previous year. The stings, while often painful, can be particularly dangerous for individuals with weakened immune systems.
MedusApp, a platform on which people report jellyfish sightings and stings, has also recorded hundreds of incidents every day throughout the summer. The app features a real-time map to help beachgoers avoid areas with high jellyfish concentrations.
Most of the jellyfish along the Catalan coast are relatively harmless species, such as the fried egg (Cotylorhiza tuberculata) and barrel (Rhizotoma pulmo) jellyfish.
However, in July, two beaches in Tarragona, southern Catalonia, were temporarily closed following the appearance of the Portuguese man o’war (Physalia physalis). Although not technically a jellyfish, this siphonophore’s sting is particularly painful and can be deadly.
Macarena Marambio, a researcher at the Institute of Marine Science in Barcelona, attributes the rise in jellyfish numbers to climate change and increasing sea temperatures. Ms Marambio, who leads the Jellyfish Alert project, said: “The jellyfish are becoming more common and are extending both their seasonal and regional presence. Warmer seas support their reproduction, leading to an increase in the purple barrel jellyfish population.”
She added that while jellyfish populations naturally fluctuate, with some years seeing more than others, the cycles are becoming shorter. She said: "In the Costa Brava, these cycles are now shorter. Some species that once peaked every eight to ten years are now doing so every two years."
In addition to the climate crisis, Ms Marambio also highlighted the impact of overfishing, which reduces natural predators, and human activities such as the construction of breakwaters, ports, and artificial beaches. These activities, she said, lower water quality, creating environments where jellyfish can thrive, such as in the port of Barcelona.
While the focus is on the Catalan coast due to the availability of data, similar trends are being observed across the Mediterranean. However, Ms Marambio cautioned that it remains unclear whether this increase in jellyfish numbers is a long-term trend.
“We know that environmental conditions are changing, and while we can model potential outcomes, it’s difficult to predict how the broader ecosystem will adapt,” Marambio said. “For now, warmer seas are conducive to jellyfish blooms, but it’s uncertain what will happen if temperatures continue to rise.”
In the meantime, beachgoers may need to prepare for more frequent encounters with these marine creatures.
Josep Maria Gili, Marambio’s colleague at the Institute, added, “There’s no immediate solution because this is tied to climate change. We’ll have to adapt to sharing our beaches with jellyfish.”
