Why do some jellyfish blooms appear in huge swarms?

Jellyfish blooms happen when environmental conditions strongly favor survival and reproduction. Warmer seas can speed up development, and nutrient-rich waters can boost plankton, which many jellyfish and their larvae eat. Overfishing may also reduce predators and competitors, allowing jellyfish populations to expand. Some species, such as the moon jellyfish, can produce large blooms in coastal waters around the world when conditions line up. Scientists have reported major blooms in places like the Mediterranean Sea and the Sea of Japan, where blooms can disrupt fishing, tourism, and power plant intakes.