Breeding places, population dynamics, and distribution of the giant jellyfish Nemopilema nomurai (Scyphozoa: Rhizostomeae) in the Yellow Sea and the East China Sea

Abstract

In East Asian waters, concern about giant jellyfish blooms, including Nemopilemanomurai (Cnidaria: Scyphozoa: Rhizostomeae), has increased in recent decades. Based on surveys in 2012 and 2013, as a part of the Chinese Jellyfish 973 Program, we investigated the life cycle in situ of the planktonic stages of this species in the Yellow Sea and the East China Sea. We found the following results: (1) Offshore of the Changjiang River is one of its principal breeding places, and is the area where the pelagic stages of N. nomurai appear earliest in the YS and ECS. (2) The general distribution pattern of pelagic stages of N. nomurai described previously in the YS and ECS is confirmed from the 2012 and 2013 surveys: From this small area (31.50–33.00°N, 122.00–122.75°E) usually in late May and early June, it expanded into the 31.5–36°N sea area (aggregating in 32–34°N) in June, then continued to expand northward and southward to 30–37°N by August, and then shrank to 34–37°N in October. (3) The biomass and abundance of N. nomurai in 2012 both in June and August were higher than those in 2013. (4) We confirmed that almost all pelagic stages of N. nomurai in the YS and ECS were confined north of 30°N. The breeding places, population dynamics, and mechanism of formation of the distribution pattern of N. nomurai in the YS and ECS in recent years are presented.