The Giant Jellyfish Nemopilema nomurai in East Asian Marginal Seas

Abstract

The giant jellyfish Nemopilema nomurai is unique in both its enormous body size and its propensity for occasional population explosions in the East Asian Marginal Seas (i.e., the Bohai, Yellow, East China, and Japan Seas). Its frequent blooms in the last decade (i.e., in 7 out of 10 years between 2002 and 2011) have caused severe damage to local fisheries in Japan and Korea. The blooms may be attributable to environmental/ecosystem conditions conducive to such outbreaks that have prevailed in Chinese coastal waters, which are a seeding and nursery ground. One of the most characteristic features of the asexual reproduction of this species lies in its podocysts, a resting stage capable of dormancy for at least 6 years prior to excystment into active and strobilating polyps. Thus, the abundance and behavior of podocysts in a given season may determine the population size of medusae in the next season. At present, the year-to-year variation in bloom intensity can be forecast in early summer based on on-deck sighting surveys from ferries of young medusae en route from the seeding waters to the Japan Sea. Thereby, fishermen can prepare countermeasures well in advance for likely jellyfish outbursts.