The study shows that phytoplankton is both bottom-up controlled by low availability of nutrients and top-down controlled by secondary producers. The estuary imports nutrients from the sea, which are transported to the middle estuary by diffusion generated by tidal oscillation and exports phytoplankton, organic matter and zooplankton. Residence time is in the order of two weeks, being in the order of days in the lower estuary.

Concentration of phytoplankton is more than 95% of the time, below 5mg Chl a/L showing that the trophic level of the estuary can be classified as low, as it was classified by IMAR, which as collected historical field data and applied the NEEA-NOAA index for classifying the trophic level of the estuary.

A scenario of doubling the nutrients load was also simulated. In this scenario, the bottom-up limiting factor of phytoplankton was reduced, the carrying capacity of secondary producers was increased, but the estuary would still import nutrients from the sea. The maintenance of phytoplankton biomass and the increase of zooplankton biomass is a result of top-down control of phytoplankton concentration