During ebb tide, for each experiment, fifty Plexiglas circular plates (∅ 7 cm) were placed in an intertidal mudflat located in the Mondego estuary. To ensure the attachment of macroalgal spores to the surface of the Plexiglas plates, because the surface properties greatly affect settlement success (Lobban and Harrison, 1994), the plates had a rough surface,which favoured the adhesion of the spores. The replicates were hung from a rope that became submerged during high tide. They were placed 10 cm apart from each other and 20–30 cm above the sediment surface, in order to prevent sediment particles deposition. Two days later, the plates were collected and transported to the laboratory in a cooler within 1 h.