Response of the proto- and small metazooplankton assemblage during an iron fertilization experiment in the Polar Frontal Zone of the Southern Ocean

Abstract

This thesis provides a comprehensive assessment of the response and vertical distribution of major components of the pelagic ecosystem and highlights the species interactions shaping this open ocean environment and its associated biogeochemical cycles.During the iron fertilization experiment (EisenEx), carried out in the Polar Frontal Zone of the Southern Ocean in austral spring (November), the composition, succession and temporal development of the nano-, microprotozooplankton (protozoa between 2 and 20 µm and 20 and 200 µm respectively), mesozooplankton (protozoa > 200 µm) and small metazooplankton (copepod nauplii, copepodites and adults of small species) assemblage was successfully followed for three weeks and compared with non-fertilized, surrounding water. The grazing impact of microprotozooplankton on the natural phytoplankton assemblage was also studied under controlled conditions using the dark incubation method. These experimental results combined with data on microphyto- and microprotozooplankton composition and temporal development were used to estimate microprotozoan grazing impact on primary producers, in particular the diatoms, during the fertilization experiment. The temporal development of particles produced by proto and small metazooplankton (empty diatom frustules, fecal pellets, skeletons and empty loricae) and their contribution to carbon and silica vertical fluxes during EisenEx were also investigated.