The potential role of podocysts in perpetuation of the common jellyfish Aurelia aurita s.l. (Cnidaria: Scyphozoa) in anthropogenically perturbed coastal waters

Abstract

Common moon jellyfish, Aurelia spp. bloom seasonally in eutrophic or polluted coastal waters around the world. We hypothesized that podocysts, a part of asexual reproduction of the benthic polyps, were important in perpetuating populations of Aurelia aurita s.l. in anthropogenically perturbed waters. We examined the effects of temperature, salinity, dissolved oxygen concentrations, and food on the encystment and excystment of A. aurita podocysts. Podocysts were formed only by unfed or poorly-fed polyps (≤4.8 μg C polyp−1 day−1), indicating that starvation was the primary cause of encystment, while increased temperatures accelerated podocyst production rate. Encystment was never induced by changed salinity (15–32) or dissolved oxygen concentration (1–5 mg O2 l−1). Excystment occurred only when podocysts were returned to 19°C from 28°C and to oxic waters from hypoxic (0.2–1.0 mg O2 l−1). The podocysts were capable of surviving for up to 3.2 year. Histology revealed that newly-formed podocysts contained rich organic reserves (e.g., carbohydrate, protein, and lipid) that were gradually consumed while encysted. Podocysts may contribute minimally to increasing A. aurita polyp abundance, but they can insure maintenance of the population in adverse environmental conditions and in predator attacks. Podocysts may also enable the population to extend to areas where polyp survival is marginal.