Abstract:The size of medusa populations in most scyphozoan species can be affected by the size of their benthic polyp populations, which reproduce asexually to give birth to planktonic ephyrae, but also are subject to predation by natural enemies. In this study, five gastropod species (Calliostoma unicum, Pleurobranchaea japonica, Hermissenda crassicornis, Sakuraeolis enosimensis and S. sakuracea) and three crustacean species (Rhynchocinetes uritai, Latreutes anoplonyx and Hyastenus diacanthus) were found to prey on polyps of the moon jellyfish, Aurelia aurita s.l., in Japanese coastal waters. In particular, C. unicum, P. japonica, H. crassicornis, R. uritai and H. diacanthus consumed more than 300 polyps per predator per day in the laboratory. These predators are common on natural rocky or pebbled seabeds, but are very scarce on various substrates in concrete-walled fishing ports, particularly on the undersurfaces of floating piers, where A. aurita polyps are attached in abundance. Transplanting natural predators to substrates with dense polyp colonies, just prior to their seasonal strobilation, is a possible countermeasure to prevent recurrent medusa blooms.

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Infections with the pennellid Peniculus minuticaudae Shiino, 1956 occurred on three species of marine fishes, the unicorn leatherjacket filefish, Aluterus monoceros (L.), the hairfinned leatherjacket, Paramonacanthus japonicus (Tilesius), and the brown-banded butterflyfish, Roa modesta (Temminck & Schlegel), held at a public aquarium in Kagoshima, Japan. Using specimens from the aquarium and type material, the postmetamorphic and premetamorphic adult females of P. minuticaudae are redescribed. The adult male, copepodid I, and late chalimus stages are described for the first time. The three fish species represent new host records for P. minuticaudae. Fishes were found heavily infected with P. minuticaudae, and extensive lesions associated with infections were found on the skin and around the fin rays of R. modesta. While pennellids usually use two hosts during their life cycle, it is very likely that P. minuticaudae completes its life cycle using one host, as suggested by copepodids, chalimi, adult males, premetamorphic adult females, and postmetamorphic adult females of the parasite all being found on a single fish.