Jellyfish numbers are increasing worldwide for several reasons. These include overfishing of their predators, declining populations of other fish that compete with jellyfish for food, warmer ocean temperatures that help jellyfish thrive, and pollution from fertilizers that boost plankton growth, a key part of jellyfish diets. Check out the map to see how sea surface temperatures have changed globally over 25 years (data provided by the Copernicus Marine Service).