Mediterranean

The Mediterranean nearly vanished 5.5 million years ago—evaporating into a salt desert three kilometers below sea level—then refilled in a megaflood so violent it carved 1,000 cubic kilometers of bedrock and created most of today's genetic diversity in under two decades. The basin now hosts 7.5% of the world's marine species in 0.7% of its ocean area, a tenfold concentration that makes it simultaneously the planet's most productive and most vulnerable maritime ecosystem.

The Mediterranean's story begins with catastrophe. Between 5.96 and 5.33 million years ago, tectonic shifts closed the Strait of Gibraltar, isolating the basin from the Atlantic. Within a thousand years, evaporation exceeded river inflow, and the sea dried to hypersaline lakes surrounded by salt flats—the Messinian salinity crisis. Salt deposits exceeding one million cubic kilometers accumulated, some more than three kilometers thick. Rivers like the Nile carved canyons 2,400 meters deep pursuing the retreating waterline. Of 779 endemic species, only 86 survived. The Mediterranean had become biology's greatest extinction event outside the dinosaur era—and its greatest comeback story was about to begin.

Then, 5.33 million years ago, the Gibraltar barrier broke. The Zanclean megaflood refilled the basin in an estimated 2 to 16 years—sea levels rising ten meters per day at peak flow, discharge rates 1,000 times greater than the modern Amazon. This catastrophic recolonization created one of evolution's most productive founder events. Species radiating from refugia into empty niches generated the endemic richness that defines the basin today: 48% of sponge species found nowhere else, 35% of sea squirts, 24% of echinoderms, 22% of seagrasses. Among those seagrasses, Posidonia oceanica is entirely endemic to the Mediterranean, building unique carbon-storing "matte" structures that persist for millennia and provide the basin's primary blue carbon sink.

For five thousand years, this nearly enclosed sea served as the incubator of Western civilization. Phoenician traders, Greek colonists, Roman galleys, Byzantine merchants, Venetian convoys, and Ottoman fleets all exploited the same geographic logic: a narrow sea connecting three continents, with predictable winds, sheltered harbors, and island stepping-stones that reduced open-water crossings. The "Mediterranean trinity"—wheat, grapes, and olives—emerged from the unique climate: wet winters, dry summers, and reliable seasonality that enabled agricultural planning impossible in wetter northern Europe.

The 1869 opening of the Suez Canal fundamentally altered the ecosystem's trajectory. Before the canal, Mediterranean and Red Sea biota had been separated for millions of years. Lessepsian migration—named for canal builder Ferdinand de Lesseps—has since introduced nearly 1,000 alien species. Red Sea species, adapted to higher salinity and lower nutrients, outcompete Atlantic-derived Mediterranean natives through competitive exclusion. The goldband goatfish displaced native red mullet in Israeli waters; warming enables tropical invaders to colonize ever-farther north and west. The Mediterranean faces another phase transition, this time measured in decades rather than millennia.

The Mediterranean basin houses 512 million people across 22 nations, generating $5.6 trillion in ecosystem services. Tourism dominates at 92% of Gross Marine Product: Italy, Spain, France, and Turkey contribute the largest shares. The Strait of Gibraltar sees 110,000 vessel transits annually; the Suez Canal normally handles 12% of global seaborne trade, though Houthi attacks diverted most major carriers around Africa through 2025—CMA CGM's Jacques Saade, one of the world's largest container ships, returned to the Suez route in December 2025, signaling fragile recovery.

Yet the productivity masks fragility. Over 80% of assessed fish stocks are overfished, with hake, sole, and red mullet populations collapsed along many coasts. Posidonia meadows have declined by 13-38% since the 1960s. The African-Eurasian flyway funnels 2 billion birds through Gibraltar and the Bosphorus twice yearly, but an estimated 25 million are killed annually in the crossing. Climate projections show the eastern Mediterranean warming faster than almost any marine region on Earth; under high-emissions scenarios, the basin becomes functionally tropical by 2100.

The lesson from the Messinian is clear: the Mediterranean has survived phase transitions before, but recovery took 1.7 million years. The sea that nearly vanished and came back stronger is facing another transformation—but this time, humans are running the clock.