Throughout my scientific career I have addressed several aspects related to the ecology of marine zooplankton. Starting from a focus on marine secondary production and the function of mesozooplankton (mostly copepods) in the dynamics of marine ecosystems, I gradually switched to the study of the function of microzooplankton in pelagic food webs. This is the line that defines my current research, and which I intend to continue developing in the future. Some of my work in the field of marine microzooplankton ecology is used today as obligated reference when describing the relevance of this group in the flow of matter and energy in the marine ecosystem. From a first generalist approach, I have tried to open the black box of the microzooplankton and estimate the specific function of some of its groups (or species) in the plankton trophic networks. Also, I have been quite interested in studying particular aspects of the ecophysiology of microzooplankton in response to ambient variables. My latest interest is on the role of mixotrophy in the marine food web.