三种大型钵水母幼体对牙鲆和许氏平鲉仔稚鱼的捕食选择性

为探讨中国近海常见大型钵水母对鱼类资源补充的影响,本实验利用清除率法比较研究了伞径4 cm的3种大型水母幼体—海月水母(Aurelia aurita)、海蜇(Rhopilema esculentum)和沙海蜇(Nemopilema nomurai),对不同发育阶段的牙鲆(Paralichthys olivaceus)和许氏平鲉(Sebastes schlegeli)仔稚鱼的捕食量。结果表明,3种水母均可捕食牙鲆和许氏平鲉仔稚鱼,其捕食率随仔稚鱼生长而降低,其中海月水母可捕食规格15 mm牙鲆和20 mm许氏平鲉,海蜇能够捕食规格20 mm牙鲆和30 mm许氏平鲉,沙海蜇可捕食30 mm许氏平鲉;仔稚鱼密度对水母捕食率影响不显著,牙鲆的变态和底栖生活是其逃避被水母捕食的有效手段;不同水母物种对仔稚鱼的捕食效率主要与其活力相关,水母结构和毒性也是重要因素,相同规格3种水母对仔稚鱼捕食率由高到低为海蜇沙海蜇海月水母。本研究结果可为阐明水母与鱼类的动态关系,研究海洋鱼类的自然资源补充机制提供参考。

Predation of three juvenile scyphomedusa species to Paralichthys olivaceus and Sebastes schlegeli larvae

Jellyfish bloom has had numerous deleterious effects in the marine ecosystem worldwide in past decades. In particular, jellyfish bloom impedes the recovery of fish stocks by preying on fish eggs and larvae, and competing strongly for food with fish. Recently, studies have focused on the predatory relationship between fish and jellyfish. However, the species involved vary among different jellyfish-bloom areas.Aurelia aurita,Rhopilema esculentum and Nemopilema nomuraiare, the three common jellyfish species along Chinese coastal seas, of whichA. auritais a cos-mopolitan jellyfish species, and the other two species were indigenous. To the best of our knowledge, the predatory ability of different jellyfish species has not been estimated, as well as the predation of jellyfish on larger fish larvae (more than 10 mm). In this study, the predation of three common jellyfish species (A. aurita,R. esculentum andN. no-murai), as 4-cm medusae, in Chinese coastal seas on fish larvae ofParalichthys olivaceus and Sebastes schlegeli, was studied using the clearance method. All three jellyfish species could prey on fish larvae, and their predatory abilities decreased as the fish grew. The ranges ofA. auritato P. olivaceus and S. schlegeli were not bigger than 15 mm and 20 mm, respectively; the ranges ofR. esculentumto P. olivaceus and S. schlegeli were not bigger than 20 mm and 30 mm, respectively; and the ranges ofN. nomuraito S. schlegeli were not bigger 30 mm (the experiment ofN. nomurai toP. olivaceuswas not done). Clearance rates were similar between the different prey concentrations, and metamorphosis of P. olivaceushelped to avoid predation. The clearance rates of different jellyfish species mainly depended on their vital-ity, though body structure and toxicity of jellyfish were also important factors. Accordingly,R. esculentum had the highest vitality and predatory ability toward fish larvae, followed byN. nomurai andA. aurita. The results provide theoretical evidence of the relationship between fish and jellyfish, and will further the study of the recruitment mecha-nisms of natural fish resources in Chinese seas.