Natural predators of polyps of three scyphozoans: Nemopilema nomurai, Aurelia coerulea, and Rhopilema esculentum

Jellyfish blooms have become a hot research topic in recent decades because they pose a serious threat to fisheries, coastal industries, tourism, and the marine ecosystem. The life cycle of scyphozoan jellyfish consists of a pelagic medusa stage and a benthic polyp stage, where asexual reproduction and strobilation of the polyps directly affect the abundance of ephyra and subsequently medusa abundance. The dynamics of polyps are affected by both environmental and biological factors, and predation by natural predators is one of the most important biological factors. Nemopilema nomurai, Aurelia coerulea, and Rhopilema esculentum are three scyphozoan species that are commonly found in Chinese coastal waters, and previous studies reported that the survivorship of polyps differs among the three species when they are exposed to the same benthic community. To identify potential natural predators of polyps of these three species in Chinese coastal waters and to determine whether the predation rates on polyps of the three species differ, we collected 39 species of macrozoobenthos from the Bohai Sea, Yellow Sea, and East China Sea from May 2014 to June 2016 and conducted predation tests and predation rate measurements. We found that the nudibranchs Pleurobranchaea novaezealandiae, Okenia plana, and Chromodoris tinctoria and the sea anemones Paracalliactis sinica, Calliactis japonica, Anthopleura incerta, and Anthopleura midori could prey on the polyps of all three scyphozoan species. The predation rates increased with the body length of the predators. The predations rates were also related to the polyp species, although the different predators showed no consistent preference for a particular species of polyp. Our results indicate that introducing predators to locations inhabited by polyps might be a way to control the benthic polyp populations and prevent subsequent jellyfish blooms.