Are jellyfish taking over the ocean?

Bobbing on the surface of the waves or letting themselves be carried by the current, jellyfish are among the oldest creatures in the oceans. 

However, they are increasingly seen as a problem: some scientists have observed that so-called ‘jellyfish blooms’ are occurring more frequently.

A ‘bloom’ is a rapid, temporary increase in jellyfish reproduction rates. It can lead to gigantic clusters composed of hundreds of thousands of these marine animals.

Two factors have been identified as contributing to this natural phenomenon: climate change and human impact on the seas, such as overfishing.

Both have created better conditions for jellyfish, which can thrive in environments where other species struggle to survive.

At the same time, jellyfish blooms are having negative effects on both human and marine life.

These swarms of sea jellies can compete for food with fish, damage fishing nets and coastal infrastructure, and pose a threat to swimmers.

The Spanish Mediterranean is one of the areas where scientists have observed increasing numbers of jellyfish. Data from 11 Catalan beaches shows that, in the summer of 2024, 43% of beach injuries were caused by jellyfish stings. 

In an attempt to find solutions, experts are shifting their focus, using jellyfish as a resource or trying to mitigate the root causes of their proliferation. 

But some scientists are advocating for a more cautious approach, not least because jellyfish also have a positive role to play in their ecosystem.

Watch our explainer above to find out more.

Journalist • Cristina Coellen

Video editor • Jean-Christophe Marcaud