Top-down and bottom-up control of phytoplankton in a mid-latitude continental shelf ecosystem

•The top-down control by mesozooplankton is a determining factor for the dynamics of phytoplankton biomass in the Gulf of Cadiz.•Resource availability influences phytoplankton dynamics, but grazing-induced top-down control limits biomass magnitude.•The relative importance of top-down and bottom-up control exhibits a complex pattern dependent on spatiotemporal variability.