| Aurelia sp.1(Linnaeus,1758), also called moon jellyfish, is a kind ofthe cosmopolitan, neritic scyphomedusa animal which belongs to Cnidaria,Scyphozoa, Semaeostomeae, Ulmaridae, Aurelia. It distributs along the seacoast reef and shallow sea area of the Bohai Sea,yellow sea, the East ChinaSea, the south China sea. In recent years, with the influence on oceanecosystem caused by human activities, the discountinuity outbreak ofAurelia sp.1in various waters has caused serious ecological problems.Some researches on this jellyfish had been regarded as one of hot issues inecology field in china. However, research achievements in this field werenot sufficient. This study not only supply some evidences to distinguish thetwo species morphologically and revealed the predatory effects ofCharybdis japonica to various life stages of Aurelia sp.1and Rhopilemaesculentum preliminarily, but also provided theory reference usingbiological method to prevent and control Aurelia sp.1outbreaking alongChina’s coastline.1. Comparison on ephyrae characteristics of Aurelia sp.1andRhopilema esculentumIn order to solve the difficulty of distinguishing Aurelia sp.1and R.esculentum in the ephyrae stage of their life cycles in ocean resourcesinvestigation and morphological classification, some characteristics of organ forms of Aurelia sp.1and R.esculentum were observed andsummarized in ephyrae stage. The umbrella diameter, sensory tentaclelength and width of ephyrae of Aurelia sp.1and R. esculentum was about250~350μm,50~80μm and800~1200μm, respectively. Besides thesecommons, some distinctions between the two species were showed: thebody color variation and oral arms’ development were the most remarkabledissimilarities. This study showed that the body color of Aurelia sp.1in theearly ephyrae stage was red purple, and it turned to be light in late ephyraestage while the color of R. esculentum was white and transparent. There arefour oral arms developing into dagger-shaped tentacles in larval stage ofAurelia sp.1; however, each of the four oral arms turned into two parts andgrew out filiform and baculiform tentacles in R. esculentum. There aresome significant differences in body color, oral arm’s appearance andswimming behavior in ephyrae stage of Aurelia sp.1and R. esculentum;particularly, the change of body color and the characteristics of oral armmay be regarded as evidences to distinguish the two speciesmorphologically.2. The mutual predatory relationship of jellyfishes in different stagesof life circle between Aurelia sp.1and Rhopilema esculentaA laboratory experiment was conducted to study the predator-preyrelationship of different life stages between Aurelia sp.1and R. esculenta.The results showed that Scyphistomae of Aurelia sp.1, with1mm oral diskdiameter, could prey on ephyrae and medusa of R. esculenta whose oraldisk was no more than8mm in diameter; and in the ephyrae larval stage,Aurelia sp.1was able to prey on R. esculenta’s; Aurelia sp.1medusa with100mm bell diameter could still feed upon both ephyrae larval and earlymedusa (bell diameter30mm) of R. esculenta. However, the early medusa of R. esculenta with the diameter of umbrella was no less than10mm couldabsolutely prey on Aurelia sp.1ephyrae larval. This study suggests thatAurelia sp.1had stronger ability to prey on R. esculenta rather than waspreyed by the other one. These results not only revealed the relationshipbetween the outbreak of Aurelia sp.1and the decrease of R. esculentaresource in some way,but also be helpful to improve the artificialenhancement and releasing effect of R. esculenta.3. Predation abilities on five kinds of small organisms by Aurelia sp.1A laboratory experiment was conducted to reveal the predation abilityon Artemia nauplii (0.50±0.10mm), Sebastodes fuscescens (5.8±0.30mm),Mysis (2.50±0.20), Harpacticus Uniremis Kroyer (1.28±0.05) and CrabZoea (1.500.30) by2.5cm umbrella diameter’s Aurelia sp.1in24h. Theresult showed that preyed rate of Artemia nauplii and Mysis by jellyfishwas much higher than those of Harpacticus Uniremis Kroyer and CrabZoea at500ind./L level. Almost Sebastodes fuscescens were killed orpreyed in100ind./L level, and the predation rate reached93.2﹪. The resultalso suggested that palatability, swimming speed, escaping strategy andsome morphological characteristics (body style and structure) of prey hadnegative influence on predation effects. It indicated that was the mutualeffect among all factors decided the predation effects not just by one.4. Study on predatory relationship among Charybdis japonica, Aureliasp.1and Rhopilema esculentaA laboratory experiment was aimed to study the predatory effects of C.japonica (body weight:37.58±6.09g, body length:5.59±0.35cm, bodyheight:3.95±0.29cm) to various life stages of Aurelia sp.1and R. esculenta.There was no apparent predacious phenomenon happened when fed polypsor ephyrae of Aurelia sp.1and R. esculenta to C. japonica respectively. The consumption of R. esculenta larval with1~2cm umbrella diameter byJapanese swimming crab was about102.08g per day; but fewer larval with4~4.5cm or7~8cm umbrella diameter was caught and consumed. Theresult also showed that C. japonica consumed all size classes Aurelia sp.1medusa (3~5cm;7~10cm and17~20cm in UD), and it took177.12g~196.56g medusa per day. C. japonica also caught and ate themixed baits synchronously which consisted of1~2cm UD R. esculentalarval and one of the three size classes of Aurelia sp.1medusa diameters(3~5cm;7~10cm and17~20cm), while the selectivity indicted for preyshowed that Aurelia sp.1medusa was preferred (p<0.05). This study notonly revealed the predatory effects of C. japonica to various life stages ofAurelia sp.1and R. esculenta preliminarily, but also suggested theinfluence on population quantity of Aurelia sp.1medsusa and R. esculentaby C. japonica along china ocean area from a food chain perspective. Thissuggested that Aurelia sp.1could not provid wild crabs the main nutritionalrequirements for normal growth. Therefore, the nutritional value of Aureliasp.1for predators need further research. |
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