They don't have brains, bones or even hearts, yet jellyfish have pulsed through Earth's oceans for half a billion years. Their habitats face growing threats from pollution, nutrient-rich runoff and ocean acidification—pressures that make marine conservation essential to restoring coral health and sustaining the species that depend on these waters.

Don't be fooled by the 'fish' in their name: they belong to the invertebrate club called Cnidaria and they're made up of about 95% water. With their bell-shaped bodies and trailing tentacles, they're more like ocean drifters than deep-sea athletes. Some glow like the one pictured here in the Pacific Ocean off Guerrero, Mexico, while others pack stings. India's coasts have had their notable encounters too. Off the east coast, scientists recorded a bloom of venomous box jellyfish in the Gulf of Mannar in 2021.

Jellyfish are vital links in the food chain, feeding turtles, sunfish and seabirds. Their sudden population booms also act as alarms, signalling changes in the ocean caused by warming waters and overfishing. These brainless blobs have outlived dinosaurs, mastered the art of drifting and proved that sometimes being spineless is actually a strength.