Region IV – Bay of Biscay and Iberian Coast
In Region IV, branches of the North Atlantic Current bend round towards the south. Beyond the shelf break, Atlantic water interacts with salty Mediterranean water, which then moves northward along the continental slope. Off the Iberian Peninsula, northerly winds cause an upwelling of cold and nutrient-rich deeper water to the surface during summer.
Region IV corresponds to the Lusitanean zone and is highly diverse with many different types of coastal habitat, such as rocky cliffs, shingle, sandy and muddy shores, rias, coastal lagoons, open bays and estuaries. The waters of the shelf host maerl beds and sea-pen and burrowing megafauna communities. Many northern species reach the southern limit of their distribution in Region IV and many southern species reach their northern limit of distribution. Mediterranean species occur in the south. Areas of upwelling off the Iberian coast are responsible for the spring bloom occurring earlier than in the other Regions. These areas are highly productive and have supported large populations of pelagic fish such as sardine. The continental shelf hosts cold-water corals and deep-sea sponge aggregations and is dissected by large submarine canyon systems which provide a pathway to the deep sea for sediment and nutrients and contain diverse biological communities with many endemic species.