Short answers, pulled from the story.
The Messinian salinity crisis occurred around 5.97 million years ago when the connection between the Mediterranean Sea and the Atlantic Ocean progressively restricted until total closure. This event lasted approximately 640,000 years before the Atlantic-Mediterranean connection was completely reestablished by the Zanclean flood around 5.33 million years ago.
A resident orca pod of some 36 individuals lives around the Strait of Gibraltar, which is one of the few remaining pods in Western European waters. Hundreds of thousands of seabirds including Scopoli's shearwaters, Balearic shearwaters, Audouin's gulls, lesser black-backed gulls, razorbills, and Atlantic puffins use the area annually to migrate between the Mediterranean and the Atlantic.
Evidence of the first human habitation of the area by Neanderthals dates back 125,000 years ago with their presence there dating as recently as 24,000 years ago. Archaeological evidence of Homo sapiens habitation of the area dates back thousands of years while various groups including Carthaginians, Romans, Vandals, Moors, and Berbers have crossed the strait throughout history.
Water flows more or less continuously eastwards and westwards because a smaller amount of deeper saltier and denser waters continually flow westwards as the Mediterranean outflow while a larger amount of surface waters with lower salinity and density continually flow eastwards as the Mediterranean inflow. The Camarinal Sill at the far western end limits mixing between the cold less saline Atlantic water and the warmer more saline Mediterranean waters creating distinct layers.
During the Second World War German U-boats used the currents to pass into the Mediterranean Sea without detection from September 1941 to May 1944 when Germany managed to send 62 U-boats into the region. Nine U-boats were sunk while attempting passage through the British-controlled Strait of Gibraltar and 10 more had to break off their run due to damage before reaching their destination.