The Effect Of Temperature And Food Supply On The Asexual Reproduction And Ontogeny Of Aurelia Sp.1

In recent decades,a significant increase in jellyfish blooms has been observed worldwide,which is regarded as a response to climate change and anthropogenic disturbance.The moon jellyfish Aurelia spp.are among the main blooming jellyfish species,causing greate damage to the health of marine ecosystem and the sustainability of fish resources utilization.In this study,Aurelia sp.1,the common blooming species in China coastal waters,was studied via laboratory controlled experiments to determine the effect of temperature and prey concentration on the polyp,ephyra and medusa stage of its life history.The prey used was Artemia nauplius.Major findings and conclusions are listed as follows:To determine the combined effect of temperature and food conditions on Aurelia sp.1 asexual reproduction(budding and strobilation),the rising-and decreasing-temperature experiment was designed to simulate the warming and cooling process on the basis of annual sea temperature.Results showed that food condition would affect both the size of the Aurelia sp.1 polyp population and juvenile medusa population,whereas temperature adjusts the reproductive energy distribution between budding and ephyra release to regulate the strobilation process.Among the temperatures tested,13oC was most appropriate for polyps to release ephyrae,while bud production was highest at 15oC.By using the law of effective accumulated temperature,the thermal constant and threshold temperature of Aurelia sp.1 strobilation were calculated for the first time.Results showed that in the rising-temperature experiment,the thermal constant was 265.4 daysoC,and the threshold temperature was 4.7oC.While in the decreasing-temperature experiment,the thermal constant in 147.2 daysoC,and the threshold temperature was 2.7oC.The increase of effective accumulated temperature would contribute to increase the strobilation rate of Aurelia sp.1 polyp population,however it had no significantly effect on the number of ephyrae released.When the accumulated temperature exceed the strobilation thermal constant,increasing in water temperature as a stimulation could accelerate the development rate of polyps and shorten the process of ephyrae releasing.This experiment revealed the gene expression change of Aurelia sp.1 during polyp strobilation process.AureStrolin was supposed to be the gene regulation to induce strobilation reproductive.Retinoic acid pathway might alter gene expression pattern to induce the differentiation of polyp muscle tissue and through GTP-binding regulatory proteins signal transduction pathway,furthmore to undergo metamorphosis process.The methylation process also played an important role in the process and maintenance of Aurelia sp.1 strobilation.The experiment in ephyra stage was designed to determine the effect of temperature and prey concentration on ephyra production,initial bell diameters,mortality,and the ontogenetic process.The result showed that temperature and food availability affect the condition of the Aurelia sp.1 parental polyp population,which in turn determines the ephyra population size and the initial organic content of each ephyra.As the food supply increases,the production of ephyrae increases,duration of development shortens and mortality decreases.For this reason,in spring a longer strobilation temperature and relatively higher zooplankton biomass contribute to blooms of Aurelia sp.1.However,the ephyrae released in autumn and winter would face severely food limited conditions,their low resistance to starvation must lead to increased mortality.Therefore,the Aurelia sp.1 ephyrae produced in autumn are not the main source of the medusa population in the next year.Laboratory experiments were designed to obtain the feeding data of Aurelia sp.1.Result showed that,in the range of prey concentration(0.25—26.11mgC/L),individual ingestion rates of Aurelia sp.1 increased linearly with the increase of the prey concentration.A significantly linear relationship was also found between the bell diameters(1-8cm)and individual feeding rates of the medusae.The medusae still fed actively,with even superfluous feeding at high prey concentration.The diel continuous feeding experiments indicated that there was no significant diurnal feeding rhythm in Aurelia sp.1 when food resource was sufficient.