Jellyfish

Jellyfish are ancient marine animals composed mostly of water. Their umbrella-shaped bell contracts rhythmically, pushing them forward, while trailing tentacles contain stinging cells called nematocysts used to capture plankton or fish. Most jellyfish drift with currents, though some can steer slowly.

The jellyfish life cycle alternates between a sessile polyp stage and the free-swimming medusa stage. Polyps bud off tiny medusae that grow into adults, reproduce, and release eggs and sperm into the water. Some species skip stages or reproduce asexually, allowing rapid population booms when conditions are right.

Jellyfish inhabit every ocean depth, including polar seas. Leatherback sea turtles, sunfish, and certain seabirds depend on them for food. In balanced ecosystems, jellyfish help recycle nutrients, but when predators decline or waters warm, jellyfish blooms can clog cooling systems, damage fishing gear, and compete with fish for plankton.

Human actions—overfishing, coastal pollution, and climate change—sometimes create favorable conditions for jellyfish swarms. However, not all jellyfish are harmful; some species glow beautifully at night, and scientists study jellyfish proteins such as GFP (green fluorescent protein) for medical research.

Beachgoers should learn local jellyfish advisories, wear protective clothing, and rinse stings with seawater (not freshwater) before seeking medical help if symptoms persist. Protecting ocean food webs and reducing pollution help keep jellyfish populations in balance.