Having affinities with the oceanic waters off the Iberian peninsula.
The "Lusitanian fauna" was discovered by Fraser, 1955. He originally defines it as "...that fauna which, originating in the outflow from the Mediterranean, has become modified by admixture with fauna from the area between the Azores and Bay of Biscay."
Fraser, 1955 continues: "It is used as a convenient term to distinguish it from the fauna of the North Atlantic Drift on the open Atlantic to the west of the British Isles..."
The northward subsurface inflow of Lusitanian plankton runs along the western side of the British Isles and reaches the surface layers due to upwelling NW off the Hebridies. From there, it flows to the east, mixing with coastal waters and it may reach the Orkneys, but rarely penetrates beyond the Shetlands. Once near the Orkneys, frequently Lusitanian plankton enters the Northern North Sea.