Light as a driver of phytoplankton growth and production in the freshwater tidal zone of a turbid estuary

► Light is usually the main driver of phytoplankton in turbid estuaries. ► We carried out light enrichment experiments under controlled conditions with phytoplankton from the freshwater tidal reaches of the Guadiana estuary. ► Phytoplankton growth was light-limited throughout the year. ► Diatoms were the most light-limited groups, in contrast to cyanobacteria. ► P-E curves suggest that phytoplankton was not acclimated to the low-light conditions that prevail in the Guadiana estuary.