Monster Jellyfish
Credit: Dan Martin/Dauphin Island Sea Lab

The Australian spotted jellyfish, Phyllorhiza punctata, have invaded the Gulf of Mexico. With plenty of food, they grow as big as dinner plates and weigh up to 25 pounds (11 kilograms), although in their native waters they tend to be much smaller. They are not dangerous to humans, but pose a threat to shrimping and fishing industries.