Single and combined effects of two trace elements (Cd and Cu) on the asexual reproduction of Aurelia sp. polyps

Jellyfish blooms are an increasingly common event in our seas. Occurring via polyps’ asexual reproduction induced by human stresses, they represent a hazard for ecosystems equilibrium. The aim of this study is to highlight polyps underrated role during these events by investigating cadmium (Cd) and copper (Cu) exposure on Aurelia sp. polyps under laboratory conditions. Cd treatments seemed to not cause toxic effects on polyps up to 1000 μg/L, while 150 μg/L of Cu resulted above polyps’ tolerance for the metal, leading to a 62% of mortality and inducing the regression-regeneration cycle of polyps. Surprisingly, combined treatments of Cd and Cu had lesser effects, working antagonistically. Our results show how, in natural conditions, the chosen concentrations and combinations could not represent a hazard for polyps, instead, they stimulate the asexual reproduction, supporting the hormesis and, through jellyfish blooms, altering the Good Environmental Status aimed by the Marine Strategy Framework Directive.