Evidence of gregarious settlement of planula larvae of the scyphozoan Aurelia aurita: an experimental study

Abstract

Laboratory and field experiments investigated whether the aggregated distribution of polyps of the scyphozoan Aurelia aurita is a result of attraction by the established polyps on the planula larvae, i. e. gregarious recruitment. Planula larvae showed an increased rate of metamorphosis in the presence of established A. aurita polyps in laboratory experiments. Petri dish experiments showed that the planula larvae were attracted to established polyps. If the polyps were replaced by mimics (sandgrains), no such attraction was observed. Transplant experiments in the field tested whether different densities of 4-d old established A. aurita polyps could affect the recruitment of conspecific planula larvae. A significant treatment effect was observed, viz. a positive correlation to initial polyp density. Results are interpreted as suggesting that the planula larvae of Aurelia aurita show gregarious behaviour. This is the first report of gregarious behaviour in the class Scyphozoa.