Mesoscale in situ iron fertilisation experiments have resulted in the build-up of phytoplankton biomass and established beyond doubt that iron availability is the key factor limiting growth rates of oceanic phytoplankton in high-nutrient, low-chlorophyll (HNLC) regimes (see poster Assmy et al.). The response of important groups (microproto-, mesoproto- and small metazooplankton) of the pelagic community and the processes within the food web were studied in detail and compared with processes in the surrounding water during two iron fertilisation experiments in austral spring (EisenEx) and summer (EIFEX)