Blooms of the giant jellyfish Nemopilema nomurai: a threat to the fisheries sustainability of the East Asian Marginal Seas

Abstract

The rhizostome jellyfish Nemopilema nomurai, which is endemic to the East Asian Marginal Seas (i.e. the Bohai, Yellow, East China and Japan Seas), is unique both by its enormous body size (ca. 2 m maximum bell diameter and 200 kg wet weight) and propensity for occasional population explosionss. Massive blooms of this species have historically been reported only once per ca. 40 years (i.e. in 1920, 1958 and 1995), but have become increasingly frequent recently (i.e. in 2002, 2003, 2005 and 2006). Both accumulated knowledge on the spatiotemporal distributions and physical modeling of the water circulation show that the medusae are released from benthic polyps during April–June in the Yellow Sea and East China Sea, and transported by the Tsushima Current to the Japan Sea. The bloom in 2005 might be the largest ever in history; as many as 3–5×10⁸ medusae passed through the Tsushima Strait daily during the summer and there were more than 100,000 complaints from commercial fishermen. The recent blooms of N. nomurai may have been caused by environmental changes, such as increased water temperature, eutrophication, coastal modification, and over-fishing in Chinese coastal waters. Frequent jellyfish blooms can apparently be a threat to the fisheries sustainability of the East Asian Marginal Seas, one of the world's most productive fisheries grounds.