Understanding the zooplankton ammonium excretion: from biogeochemical implications to intracellular regulatory mechanisms

[EN] This thesis focuses on the zooplankton NH4+ regeneration that supports about the 80% of the phytoplankton requirements. In its more oceanographic facet, it elucidates the control that the mesozooplankton community exerts on the primary productivity in the northern Benguela, and models the N-fluxes from zooplankton NH4+ excretion. At the physiological level, it examines the relationship between the NH4+ excretion and its associated biochemistry. Assuming the substrate availability as the critical factor in regulating the velocity of NH4+ production, a bisubstrate model was developed to predict its actual rate in zooplankton. Overall, this research provides knowledge about the implications of zooplankton NH4+ excretion on the biogeochemical cycles, and introduces new insights into the study of this process from enzymatic measurements.

Understanding the zooplankton ammonium excretion : from biogeochemical implications to intracellular regulatory mechanisms

[EN]Zooplankton play a key role in marine ecosystems and their biogeochemical cycles. They exert control over the primary productivity through the consumption of organic matter and, at the same time, the release of nutrients that sustains the phytoplankton growth. This thesis focuses on the NH+ 4 excretion processes related to these heterotrophic organisms that support, at a global scale, about the 80% of the phytoplankton requirements. However, thereisno clear constant pattern in the zooplankton contribution to theNH+ 4 regeneration throughout thedifferent pelagic ecosystems, so continuousmonitoring of thismetabolic processisessential at widetemporal and spatial scales...