What’s behind jellyfish ‘blooms’ and are there actually more of them?

euronews (in English)

Swarms of jellyfish near Mediterranean beaches were worrying local authorities and tourists during summer 2024. But are these animals increasing in numbers?

Transcript

00:00They make even the most experienced swimmers rush back to the shore.

00:06Brown and the yellow and the pepper ones, they're like my enemies.

00:10Often seen as huge gelatinous clusters floating in the water, jellyfish seem to swarm more

00:15and more shores and seas.

00:18But are they really taking over our oceans?

00:25Jellyfish invasions and stings made headlines on beaches in the Mediterranean in the summer

00:29of 2024.

00:30There are a few explanations.

00:35Jellyfish reproduction is complicated, but put simply, they can clone themselves in large

00:40numbers.

00:42When conditions are right, jellyfish reproduce so much that they form large so-called blooms.

00:47The jellyfish life cycle is very dependent on winter and summer condition.

00:53In some years, you have more jellyfish because all the conditions play together to facilitate

00:59reproduction of jellyfish.

01:01In some years, it's not the case.

01:04Not every jellyfish cluster is a bloom though.

01:07Sea jellies aren't very good at swimming, so wind or ocean currents can easily push

01:11them into the same spot.

01:14This is called an aggregate.

01:15However, the increase in jellyfish is likely caused by human activity.

01:21As global warming is changing conditions in the ocean, many species are struggling

01:26to survive, except for jellyfish.

01:29They are a master of adaptation and evolution.

01:32They are primitive and simple, but could cope with unfavorable conditions like the lower

01:38pH, low oxygen, which makes them more robust to cope with environmental changes that all

01:47oceans and seas are facing.

01:50With climate change, seas like the Mediterranean are experiencing longer spells of marine heat

01:54waves all year round.

01:56For some jellyfish, the warmer water is making reproduction easier.

02:01Another driver of blooms is overfishing.

02:03This means jellyfish have less competition for food and fewer predators like tuna or

02:09turtles.

02:10In the Mediterranean alone, the fishing industry accidentally catches up to 150,000 sea turtles

02:16every year.

02:18So what happens when there are too many jellyfish?

02:21The jellyfish feed on fish eggs and larvae, in some cases, and so it could have an impact

02:28on this population that, as long as the jellyfish bloom coincides with the reproduction of that

02:34species, there could be a very intense predation and, therefore, not allow this population

02:40to have their adult stock.

02:43And then this would have an impact on what would be the fisheries.

02:47Jellyfish blooms can also cause structural damage.

02:51Buildings close to the shore are a prime target.

02:54In Sweden, jellyfish swarms have clogged the cooling pipes of the Oscarsam nuclear power

02:58plant several times, even forcing it to temporarily shut down.

03:04And of course, they sting, which can lead to beach closures and negatively impact tourism.

03:09It's like fireballs in every fiber.

03:15But jellyfish are not all bad.

03:17As they glide through the different layers of water, they carry nutrients, which other

03:21marine creatures feed on.

03:23And by eating the offspring of other species, jellyfish help to maintain a balance in the

03:28food chain under the sea.

03:47One solution could be better fisheries management to help jellyfish predators recover from overfishing.

03:57It's also important to mitigate the impact of climate change on the oceans.

04:01This includes reducing greenhouse gas emissions and limiting human stress factors for marine

04:06life, such as large-scale fishing, the proliferation of coastal infrastructures, and pollution.

04:13And as long as you don't get too close, it's worth remembering that they are a beautiful

04:31sight to behold.

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