Jellyfish have outlived dinosaurs, outsmarted evolution, and still can’t be bothered to grow a brain. Somewhere, natural selection must be laughing. Yet for all their apparent simplicity, these soft, drifting marvels play a far more powerful role in our oceans than most people realise — and the planet is better for having them.
Often dismissed as little more than beach-ruining blobs or villainised for the occasional sting, jellyfish are, in truth, one of Earth’s oldest and most resilient lifeforms. They’ve been gliding through the seas for more than 500 million years, which means they were here before trees, sharks, and even the first insects took their first evolutionary breath.
But beyond their longevity, jellyfish are ecosystem engineers. Remove them, and marine life as we know it would begin to unravel.
Architects of the Ocean Food Web
It’s tempting to write jellyfish off as little more than oceanic vacuum cleaners, hoovering up plankton and fish larvae. True, they’re voracious predators, but what’s less known is how many species rely on them for survival.
The endangered leatherback sea turtle eats almost exclusively jellyfish. An adult can chomp through up to 200kg a day, a dietary devotion that keeps jelly populations in check. Tuna, sunfish, swordfish, seabirds, and even some whale species dine on them too.
The endangered leatherback sea turtle eats almost exclusively jellyfish. An adult can chomp through up to 200kg a day, a dietary devotion that keeps jelly populations in check
Marine biologist Dr. Lisa-ann Gershwin, author of Stung!, puts it simply. ‘Jellyfish are a crucial part of ocean food webs, and their removal would have a cascade of unintended consequences.’
And here’s the plot twist: jellyfish don’t just feed predators, they protect prey too. Juvenile fish often hide beneath their bells or weave between their tentacles, using jellyfish as floating, sting-protected nurseries. Think of them as the ocean’s slightly eccentric babysitters — unpredictable, but fiercely protective.
Perhaps the most impressive thing about jellyfish is what they do after they die. They keep feeding the ocean.When jellyfish sink to the seabed in what scientists call ‘jelly-falls’ – carcasses from decaying jellyfish blooms – they deliver vital nutrients to deep-sea ecosystems that rarely receive fresh food.
Perhaps the most impressive thing about jellyfish is what they do after they die. They keep feeding the ocean.When jellyfish sink to the seabed in what scientists call ‘jelly-falls’, they deliver vital nutrients to deep-sea ecosystems that rarely receive fresh food.
One study published in Proceedings of the Royal Society B found that these jelly-falls can fuel deep-sea communities for weeks, feeding worms, crustaceans, and microorganisms that form the base of deep-ocean food webs.
Jellyfish also play courier while alive. They migrate vertically — rising at night to feed at the surface and descending by day — moving nutrients, carbon, and nitrogen through different ocean layers. It’s an elegant system, minus the cost of petrol or air miles.
As oceanographer Dr. Monty Graham, a leading jellyfish expert at the University of South Alabama, notes, ‘jellyfish are important movers of energy through marine systems. They play a much bigger role than people realise in transporting carbon and supporting plankton communities.’
And planktonm the microscopic plants at the heart of ocean life, produce at least 50 per cent of the oxygen we breathe. So yes, jellyfish contribute, indirectly, to the air in your lungs right now.
Indicators of Ocean Health
Jellyfish are often portrayed as signs of environmental doom, and to an extent, they are excellent early warning alarms. Because they respond quickly to changes in temperature, salinity, and oxygen levels, jellyfish numbers can reveal the health of a marine system long before other species show visible distress.
A surge in jellyfish can indicate declining fish stocks, warming oceans, or increased pollution. A sudden absence could suggest deeper ecological imbalance. They are, in their own silent way, the ocean’s flashing dashboard lights.
While jellyfish blooms often get a bad reputation, an increase in their numbers doesn’t always spell disaster. In some cases, more jellyfish can actually benefit marine ecosystems because of what they eat.
Certain jellyfish species feed on organisms that would otherwise upset the balance of the ocean — for example, the larvae of invasive species that could spread rapidly if left unchecked, or zooplankton that graze heavily on phytoplankton. When zooplankton populations explode, they can wipe out phytoplankton, the tiny ocean plants responsible for producing a large share of the world’s oxygen. By consuming these grazers, jellyfish can help prevent harmful algal blooms and stabilise plankton populations, indirectly supporting oxygen production and keeping ecosystems in check.
Jellyfish blooms can clog power plant intakes, derail fishing nets, and ruin holiday swims — but blaming the jellyfish is like blaming bees for stinging when we poke the hive.
Most jellyfish ‘booms’ today are human-made. Overfishing removes the predators that would normally keep jelly populations in check, while pollution and fertiliser runoff create low-oxygen ‘dead zones’ where fish struggle to survive but jellyfish flourish.
Add to that the rapid warming of the oceans – a climate shift that jellyfish tolerate far better than most marine species – and it becomes clear that their population surges are less an invasion, and more a consequence of the conditions we’ve created.
In short: jellyfish aren’t the problem. They’re often the symptom of ecological imbalance — and the ones picking up the slack when other species disappear.
As National Geographic puts it, ‘Jellyfish aren’t taking over the oceans. We’re handing them the keys.’
Imagine a world without jellyfish. Sea turtles would lose their main food source. Deep-sea ecosystems would be deprived of jelly-falls. Fish nurseries would become exposed buffets for predators. Nutrient cycles would slow, impacting oxygen production and carbon absorption. The effects would ripple through food webs with alarming speed.
For creatures with no brain, no heart, and no central nervous system, jellyfish demonstrate an astonishing level of influence
Perhaps it’s time we rethink our relationship with jellyfish, not as nuisances, but as vital custodians of the ocean. They are survivors, nurturers, nutrient couriers, climate contributors, and ecological indicators. They keep systems functioning that would otherwise falter.
Next time you see one pulsing along the shoreline, resist the urge to recoil. What looks like a floating blob is, in fact, a quietly brilliant piece of ancient engineering.
The jellyfish isn’t the ocean’s villain, it’s one of its oldest protectors. And the more we learn about them, the clearer it becomes: the ocean needs jellyfish far more than jellyfish need us.
