Top-down control in a neritic plankton system by Aurelia aurita medusae - A summary

This paper summarizes earlier published results obtained for the scyphomedusa Aurelia aurita to elucidate the role of this species in the pelagic system of the Kiel Bight (western Baltic Sea). With the data now existing, it appears that the standing stocks of various plankton components are regulated by the medusae. Comparisons between different years show that increasing densities of A. aurita are associated with a sharp decline of mesozooplankton, a shift in species composition, and a pronounced increase of chlorophyll a and ultraplankton (<15 mu m) abundance. No changes were, however, observed for microphytoplankton (diatoms and dinoflagellates). A. aurita seems, therefore, to exert top-down control over the plankton community and is considerably more important than previously supposed. The medusae influence, as a result of trophic cascading, the abundance and composition of both the secondary and the primary producers. Mass occurrence of medusae leads, however, to scanty food for themselves, smaller body size and another reproduction strategy compared with years poor in medusae.