While diving in the sea near the West Indies, Dr. Darian and Brock are startled when they are attacked by a bizarre mutant life form...a creature composed entirely of seaweed, which continues to grow increasingly larger as the plant beast merges with more and more seaweed. The two divers barely escape the plant creature's two huge tendrils as they frantically swim back to the Calico. There they call upon Godzilla to deal with the creature, and while the Seaweed Monster is no match for Godzilla, the Kaiju King can't seem to severely injure the plant creature's physical substance. As the Seaweed Monster menaces a nearby inhabited island, Dr. Darian notices that a severed piece of the creature completely dried up after excessive exposure to sunlight. Thus, she directs Godzilla to drag the Seaweed Monster onto land, where the searing tropical sunlight eventually causes the plant creature to wither and die.