Jellyfish swimming in the Pacific, Guerrero, Mexico (© Christian Vizl/TANDEM Stills + Motion)

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.