Trophic diversity of the bloom-forming jellyfish community in the coastal waters of China assessed by stable isotope analysis.

A growing realization indicates that the trophic ecology of jellyfish is more diverse than once thought, yet a holistic view reflecting the trophic structure and trophodynamics in bloom-forming jellyfish community remains rare. Based on stable isotope δC and δN analysis, we estimated the trophic characteristics of common blooms jellyfish Nemopilema nomurai, Cyanea spp., Aurelia coerulea and Aequorea spp. in the coastal waters of China (CWC). Our data indicated that most of the isotopic niche space in the overall planktonic food web was occupied by the bloom-forming jellyfish community. The large spectrum of isotopic niche highlights the diverse ecological roles and potentially broad trophic relevance of these jellyfish in the food web. The substantial trophic diversity of these jellyfish resulted from the various trophic positions occupied by different taxa, complicated niche differentiation and overlap patterns, inconsistent size-based trophic variation, and spatial and temporal variation patterns. Isotopic niche comparisons indicated the presence of niche differentiation, reflecting the difference and individual-specific characteristic in resource exploitation and feeding preference among different jellyfish. Additionally, the inconsistent size-based trophic variation among groups derived from an increase in trophic level with size for Cyanea spp., A. coerulea and Aequorea spp. medusae to no change for N. nomurai medusae, which suggests the complexity in size-related trophic shift patterns within the jellyfish group. Additional diversity also arose from variation in the spatiotemporal structuring of jellyfish trophic ecology, which might be caused by the occurrence of trophic heterogeneity at the base of the planktonic food web. In conclusion, our study characterized the trophic structures of the bloom-forming jellyfish community in the CWC, and revealed their trophic diversity resulting from interspecific, intraspecific (ontogenetic), and spatiotemporal variation. These results hold strong potential to further improve the understanding of the trophic ecology and functional roles of the jellyfish community. Furthermore, this study provides a systematic and valuable isotopic data set, spanning from the food web baseline to zooplanktonic organisms and jellyfish community, against which compare with trophic investigations in future in planktonic food web of the CWC.