The world’s oceans generate more than half the oxygen we breathe and half the food we eat. Plus, they regulate our weather and climate. Yet they are perhaps the planet’s most vulnerable ecosystem.

“You see this massive body of water with its power, its waves, and its depth, and you just say, ‘Man, nothing could touch that.’ But we’re wrong. It’s fragile,” U.S. Secretary of State John Kerry said in an interview with National Geographic.

Overfishing has depleted 90 percent of large fish, such as tuna, swordfish, marlin, cod, halibut, skates, and flounder. Agricultural runoff and sewage have polluted coastal waters with nitrogen, phosphorous, and other algae-feeding nutrients, creating more than 500 large dead zones globally. Warming ocean water is 26