Study On The Key Processes Of Life Cycle Of Aurelia Sp.1

Jellyfish blooms occurred all over the world in recent years, especially the giantjellyfish blooms in the Far East seas including China coastal waters. Jellyfish bloomsdamage the structure and function of the marine ecosystem, causing many economicand social problems to the tourism because of jellyfish sting, to the coastal industriesby blocking the pipeline of its cooling system and to the fishery resources and fisheryactivities.The jellyfish Aurelia spp. appears in estuaries and bays, causing more damage tohuman because of higher frequency of human activities. Life history of Aurelia spp. iscomplex with various ecological forms, recent research showed there are manysubspecies. In this research, we studied the key process of life cycle and the life cyclecharacter of Aurelia sp.1which blooms in coastal of China. Analyzed the effect ofenvironmental factors on the life cycle and reproduction strategy, intend to reveal thekey process and mechanism of the blooms of Aurelia sp.1in coastal of China. At thesame time, Aurelia sp.1can serve as a model organism of large jellyfish, providingconsult to the research of other scyphomedusa.In this study, we examined planula of Aurelia sp.1settlement on living-oyster,oyster shell, scallop shell, floor plates, netting and PV-pipe, proliferation of polyps onthe surfaces of bamboo and cement block. The planula and polyps preferredman-made materials （floor plates, netting, and PV-pipe）. The underside of floor plateswas strongly favorable for settlement. Polyps can form new polyps population through asexual reproduction on new habitat, the expanding process was limited bypolyps population density. When the density was relatively low, polyps populationincreased rapidly, and this increase was slower when density was relatively high.Increasing litter （plastics, glass, and wood） pollution and submarine constructions（mariculture and ocean engineering） provide more attachment surface and thusenlarge the areas of polyps distribution and form larger number of polyps populations.Temperature and food play a vital role in determining asexual direction of jellyfish in its polyp stage. The combinations of four temperature grades （10,15,20and25℃） and three food levels （no food, feed once a week and feed everyday） were setup to exam Aurelia sp.1life cycle strategy. Temperature could determine thestrobilation and ephyrae release. Food determined the number of polyps. Temperaturechanging from20℃to15℃and10℃induced ephyrae release. In suitabletemperature range for strobilation, relatively higher temperature and sufficient foodenabled polyps to produce more ephyrae. At temperatures beyond range forstrobilation, sufficient food condition enabled polyp produce polyps. Highertemperature and lower food level induced higher polyp mortality. In the range ofannual temperature of Jiaozhou Bay, polyps go through low temperature process（5℃，2month） can strobilation and release ephyrae when temperature increased.Response of polyps to light density are different under different temperature, theeffect of light density on polyps number, strobilation process and number of ephyraeare not significant.Environmental factors such as temperature and food type affect the rate ofasexual reproduction of jellyfish at the polyp stage. Combinations of threetemperatures （10,15, and20°C） and four food treatments （Prorocentrum donghaiense,Skeletonema costatum, Artemia sp, nauplii, and no food） were established to examinethe asexual reproduction strategy of Aurelia sp.1. Temperature and food typedetermined the strobilation of polyps. A change from20to15°C or10°C, induced polyps to release ephyrae when food was present, but without food, polyps did notstrobilate. Groups with Artemia sp. nauplii as prey produced more polyps and ephyraethrough buds, podocysts, and strobilation. Animal prey was better than plants as food.At20°C, the mortality rate of polyps exceeded50%in plant fed and unfed polyps.The number of polyps increased rapidly with Artemia nauplii as prey. We concludethat, when animal prey is limited, plants can serve as a nutrient source and satisfy theenergy requirements for polyps at lower temperatures. High densities ofphytoplankton can be lethal to polyps at high temperatures. Abundant animal prey andsuitable temperatures are essential conditions for polyps to strobilate and releaseephyrae, leading to jellyfish blooms.Both Aurelia sp.1and Noctiluca scintillans are unwanted species that can bloom.Though low N.scintillans abundance had been recorded when Aurelia sp.1massivelyoccurred, no robust evidence exists on their interaction. In this study, inter-annualvariation of N.scintillans abundance was analyzed with field sampling data in theJiaozhouBay, and predation rate of Aurelia sp.1on N.scintillans was estimated withlaboratory incubation. During the existence period of Aurelia sp.1（April-July）,average N.scintillans abundance was1112.3and712.5ind m^-3in bloom years of2009and2011, and varied between2381.1and17565.4ind m^-3in non-bloom years. Inlaboratory, Aurelia sp.1in both ephyrae and medusa stages ingested N.scintillans insignificant amount. The feeding rate linearly increased with both the bell diameter（0.5-8cm; R²=0.3663, p<0.01） and prey concentrations (10-2000cell L^-1; R²=0.955,p<0.01). At the lowest concentration of10, the removal rate varied from0.02h^-1inephyra to0.36h^-1in8cm sized medusa. It was suggested that massively occurredAurelia sp.1can potentially depress N.scintillans abundance in natural environments.In Jiaozhou Bay, ephyrae of Aurelia sp.1appeared from May to June, whentemperature was in the range of12to18℃in spring in Jiaozhou Bay. Survival rate ofephyrae is high in low temperature but can’t develop to medusa, growth rate of ephyrae is high when temperature beyond15℃. Polyps of Aurelia sp.1survivalduring the whole year, and can go through asexual reproduction through buds andpodocyst, ephyrae released when temperature increasing in spring, planula wereproduced through sexual reproduction of adult medusa of Aurelia sp.1during July andAugust, bell diameter of Aurelia sp.1decreased and medusa of Aurelia sp.1die out atthe end of September.