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