Effect of salinity and light intensity on somatic growth and podocyst production in polyps of the giant jellyfish Nemopilema nomurai (Scyphozoa: Rhizostomeae)

Abstract

Frequent blooms of the giant jellyfish, Nemopilema nomurai, have occurred in the East Asian Marginal Seas since 2000 and have had a devastating effect on commercial fisheries. To determine the probability of future bloom development to permit effective countermeasures, it is essential to assess the influence of environmental factors on polyp development. In this study, the effects of salinity on the polyps of N. nomurai from the coastal waters of Dalian in the northern Yellow Sea were tested at salinities ranging from 2.5 to 45. The combined effects of salinity (15 and 32) and light intensity (800, 400, and 0 lux) in a 12-h light–12-h dark photoperiod were also assessed. The lower and upper salinity limits for N. nomurai polyp survival were 10 and 40, respectively. The salinity range of 20–27.5 was best for podocyst reproduction. Survival and somatic growth of polyps, and their asexual production of podocysts, were significantly greater at low to middle than at high salinities. Polyps survived, grew, and produced podocysts at all light intensities tested; however, differences in light intensity induced few statistically significant changes. These results indicated that N. nomurai polyps are adapted to survive, grow, and reproduce in estuaries and near-shore environments.