Intraguild predation by polyps of three scyphozoan jellyfish: Nemopilema nomurai, Aurelia coerulea, and Rhopilema esculentum

Abstract

Jellyfish blooms occur worldwide and have resulted in serious problems in tourism, fisheries, coastal industries, and the marine ecosystem. The life cycle of scyphozoan jellyfish consists of a pelagic medusa stage and a benthic polyp stage. Success of asexual reproduction of the polyps determines directly the number of medusae; thus, the polyp stage is the key to understanding the population dynamics of medusae. Nemopilema nomurai, Aurelia coerulea, and Rhopilema esculentum are three scyphozoan jellyfish commonly inhabit in Chinese coastal waters. Polyps of A. coerulea are easily visible, while those of N. nomurai and R. esculentum remain yet to be found in the wild. However, distribution of the medusa indicates that the polyps of all three species may occur together. To evaluate the distribution pattern of polyps of the three species and explore intraguild predation by the polyps, we conducted a laboratory experiment that considered the attachment sequence and size relationship of calyx diameter of the polyps. We found that the polyps of A. coerulea preyed on polyps of the other two species in all treatments, except when polyps of R. esculentum were bigger than those of A. coerulea. The polyps of R. esculentum preyed on the polyps of N. nomurai only when polyps of R. esculentum attached first and were bigger than those of N. nomurai. Colonies of N. nomurai polyps were rarely found in the places inhabited by A. coerulea polyps. In addition, A. coerulea polyps are known to inhabit at depths of less than 20 m in coastal sea, thus, we speculate that N. tnomurai polyp colonies might occur at depths of more than 20 m. Therefore, our finding that polyps of A. coerulea aggressively preyed on polyps of other species may help understand other such systems of jellyfish bloom in the world.