As Korea enters the height of summer, warming seas are bringing an unwelcome visitor to its coasts: jellyfish. Marine experts say rising water temperatures are driving a sharp increase in venomous jellyfish, posing growing risks not only to beachgoers but also to fishermen and coastal industries. The greatest concern is Nomura's jellyfish, one of the world's largest jellyfish species that usually originates off the coast of China and drifts into Korean waters on ocean currents. It can grow up to