Jellyfish blooms or invasions could be detected in an early phase of development if the youngest medusa stages (ephyrae) and their early growth stages (post-ephyrae) were identifiable in plankton samples but a useful identification key for ephyrae in early growth stages is lacking for most species. In the present study, the identification characteristics of adult North Sea scyphomedusae (Aurelia aurita, Cyanea capillata, Cyanea lamarckii, Chrysaora hysoscella, Rhizostoma octopus) collected around the island of Helgoland (German Bight) in July–August 2003 and 2004 are described. Planula larvae were measured and reared to polyps in the laboratory. The process of ephyrae development asexually produced by the polyps (strobilation) was photo-documented. Photographs of the ephyrae growth stages were combined with drawings of features useful for the species identification. The provided identification key allows discrimination among post-ephyrae from plankton samples, probably leading to conclusions on the development of jellyfish blooms and their causes. |
