Giant jellyfish are taking over Japan.

Giant jellyfish are overpopulating the world’s oceans, especially around Japan. Overfishing is reducing the amount natural predators and competition for jellyfish, so they are getting bigger and more populous. Increasing temperatures in ocean are also providing jellyfish with an ideal environment for growth. This is problematic, since the huge jellyfish are capable of destroying fishing nets and spoiling the fishing industry. Some of these jellyfish can get as big as 6.5 feet in diameter.
(source)