Planktic foraminifers (PF) are heterotrophic mesozooplankton of global marine abundance, being ubiquitous proxy in paleoceanography, and climate reconstruction. In turn, the individual and biomass (Corg) of PF was largely unknown due to methodological problems. To quantitatively understand the trophic position of PF within the regional and global plankton, we have developed a new analytical method, and quantified the individual biomass of 952 specimens of 26 PF species. The new non-destructive protocol is derived from the bicinchoninic acid (BCA) method, and a nano-photospectrometer is used to measure protein biomass. We tested the method on the benthic foraminifer Ammonia tepida, from fresh and frozen samples, and from culture experiments. We then applied the new method to measure PF protein-biomass of specimens from oligotrophic and eutrophic regions, including the subtropical to temperate ocean. The average individual PF biomass amounts to 0.845 μg. Our results indicate neither inter-specific differences nor any influence of the shape of test on the individual biomass. In turn, Individual PF biomass is highly correlated with test size and mass, and independent of ecologic conditions (i.e., e.g., trophic state, water depth, and temperature). Following our new method, the PF assemblage biomass was calculated from 1128 locations and water depth from the North Atlantic, Arabian Sea, Red Sea, and Caribbean, and literature data from off Japan and Oregon. A first-order estimate of the average global PF biomass production amounts to 25-100 Tg C yr−1 including juvenile individuals. The organic to inorganic carbon (Corg : Cinorg) ratio of PF populations between the surface and subsurface water column down to 2500 m water depth seems to stay constant at ~2/3, as indicated by a case study from the Azores region. Those results show an export of both Corg and Cinorg to the deep ocean, making PF part of the biological carbon pump. The results obtained in this thesis make PF a potential proxy to quantify the biomass of paleo-assemblages, and to improve our understanding of past carbon cycle and biological carbon pump.
