Abstract：
Blooms of the Rhizostomeae Nemopilema nomurai and the Semaeostomeae Cyanea nozakii have become more prominent in the coastal waters of China since the end of the 20th century. However, the trophic ecology of these jellyfish species remain incompletely understood. In this study, the trophic characterizations of N. nomurai and C. nozakii populations were assessed using stable isotope analysis (SIA), with a focus on the important bloom area offshore of the Yangtze Estuary. Our results indicated obvious trophic differences between two scyphomedusae. The higher trophic position of the C. nozakii population in the coastal planktonic food web was reflected by its relatively large δ15N value compared to that of N. nomurai. The MixSIAR model indicated that small copepods (<1000 μm) and seston were important food sources for N. nomurai, and showed a stable dietary, irrespective of N. nomurai size. Conversely, C. nozakii exhibited a more diverse diet composition, and gelatinous organisms also were an important part of the diet of C. nozakii. Moreover, a pronounced ontogenetic shift in the diet of C. nozakii was observed, consisting of an increase in the proportion of zooplanktonic prey (excluding seston) in the C. nozakii diet with diameter. This study provides isotopic evidence of the substantial difference in trophic ecology between N. nomurai and C. nozakii, which resulted from the variations in SI values and diet compositions. Inconsistent size-based variation patterns were observed in trophic ontogenetic shifts within the N. nomurai and C. nozakii groups, highlighting a need for further investigation. These results will give insights into the characteristics of trophic ecology and functional roles of Rhizostomeae and Semaeostomeae, and indicate the need for a more careful consideration of the representations of Rhizostomeae and Semaeostomeae in coastal ecosystems, so as not to underestimate the knowledge of taxon-specific ecological effects on energy flow.
摘要：
自20世纪末以来，在中国的沿海水域中，根茎Nemopilemanomurai和Cyaostomeanozakii的开花变得更加突出。然而,这些水母物种的营养生态仍未完全了解。在这项研究中,使用稳定同位素分析（SIA）评估了诺马来和诺扎氏梭菌种群的营养特征，重点是长江口近海重要的开花区。我们的结果表明两种镰刀菌之间存在明显的营养差异。与N.nomurai相比，其相对较大的δ15N值反映了沿海浮游食物网中nozakii种群的营养位置较高。MixSIAR模型表明，小型co足类动物（<1000μm）和塞斯顿是N.nomurai的重要食物来源，并显示出稳定的饮食，无论N.nomurai大小如何。相反，C.nozakii表现出更多样化的饮食组成，和凝胶状的生物也是诺扎克氏杆菌饮食的重要组成部分。此外，观察到诺扎氏梭菌饮食中明显的个体发育转变，包括在具有直径的C.nozakii饮食中浮游动物猎物（不包括塞斯顿）的比例增加。这项研究提供了同位素证据，证明N.nomurai和C.nozakii之间的营养生态存在实质性差异。这是由SI值和饮食组成的变化引起的。在N.nomurai和C.nozakii组中的营养个体发育变化中观察到不一致的基于大小的变异模式，强调需要进一步调查。这些结果将为根瘤菌的营养生态学特征和功能作用提供见解，并指出有必要更仔细地考虑沿海生态系统中的根茎和毛藻的表现，以免低估特定分类单元对能量流的生态影响的知识。
