The focus is on marine zooplankton, a taxonomically highly diverse assemblage (~7000 described species in 11 phyla and 27 functional groups). The aim is to provide general insight into the processes that generate and maintain diversity in the open ocean and to help make better predictions of the consequences of global change. Specifically, we study holoplanktonic gastropods because they are the only metazoan plankton with a fossil record and they are vulnerable to ocean acidification.