Jellyfish blooms cause trouble for humans. For one thing, a jellyfish has venom in its/it’s tentacles. The venom gets released when the jellyfish brushes against something. If that something is a person, the person gets stung. So when a jellyfish bloom appears at a beach, a whole lot of people can get stung. Its/It’s not fun getting stung by a jellyfish. But most stings cause nothing worse than a bit of pain and a rash. However, some jellyfish stings can cause vomiting or muscle aches, and a few can be fatal.
Jellyfish blooms also interfere with the operation of power plants that use ocean water to cool their machinery. If jellyfish clog up a cooling system, the power plant may have to shut down. Jellyfish can also clog up ship engines and fishing nets.