Jellyfish — Open Ocean
Quick Fact
Jellyfish have no brain, no heart, and no bones — yet they have survived five mass extinction events.
About This Species
Jellyfish are among the oldest multicellular animals on Earth, having existed for over 500 million years — predating the dinosaurs by hundreds of millions of years. Despite their simple appearance, jellyfish are sophisticated predators with complex nervous systems and remarkable survival strategies. Some species are biologically immortal, capable of reverting to their juvenile polyp stage when stressed. Jellyfish blooms are increasing globally, partly as a result of ocean warming, overfishing, and nutrient pollution.
Why It Matters
Increasing jellyfish blooms are a sign of ocean ecosystem disruption. They can outcompete fish for food and clog fishing nets and power station cooling systems, with significant economic consequences.
Transcript
Jellyfish have no brain. No heart. No bones. No blood. They're 95% water. And they've been doing just fine for over 500 million years. Jellyfish predate the dinosaurs by hundreds of millions of years. They survived every mass extinction event in Earth's history — including the one that wiped out the dinosaurs. Whatever the ocean throws at them, jellyfish endure. They're not simple, though. Jellyfish have a nervous system — a diffuse network of neurons spread throughout their body that allows them to sense light, gravity, and chemicals in the water. Some species have complex eyes. Some can navigate. Some can learn. And some are biologically immortal. Turritopsis dohrnii — the so-called immortal jellyfish — can revert to its juvenile polyp stage when stressed or injured, essentially resetting its biological clock. In theory, it can do this indefinitely. Jellyfish blooms — massive aggregations of millions of individuals — are increasing worldwide. Warmer oceans, overfishing of their predators and competitors, and nutrient pollution all favour jellyfish. In some seas, they now dominate ecosystems that were once rich with fish. They clog power station cooling systems. They collapse fisheries. They sting swimmers. But they're not the problem. They're the symptom. Jellyfish blooms are what happens when we push ocean ecosystems out of balance. They're the ocean's way of telling us something is very wrong.