*2.1. Study Area*

The largest rivers of the Iberian Peninsula other than the Ebro River discharge to the Atlantic coastal waters, draining almost two thirds of the territory along the way. In Portugal, river mouths are mostly situated in the northern part of the country, corresponding to the wettest region of the Iberian Peninsula with around 3000 mm of rain annually (Portuguese Water Atlas, https://sniamb.apambiente.pt/content/geo-visualizador, accessed on 15 April 2022).

Combined with the rain pattern, the concentration of river mouths in the Northwest Iberian coastal zone, such as the Douro, Minho, and Mondego rivers, provides the conditions required for the generation of a significant regional feature: the Western Iberia Buoyant Plume (WIBP; [10]). This is a year-round low-salinity water lens (S < 35.8), and it extends along the Northwest Iberian coast, influencing, among other things, ocean productivity (i.e., [11,12]) and larva and egg dispersal (i.e., [1,13–16]).
