Oceans cover more than two-thirds of the surface of the planet - yet they are still not fully understood.
The world's oceans play an important role in the Earth's climate system, and millions of people depend on them directly for sustenance. People also traverse the oceans, and use them to transport goods. Yet the world's oceans are in trouble, as warming and acidification take their toll. They've also become a garbage dump for the planet, with consequences for marine life.
Much of the CO2 we emit through the burning of fossil fuels ends up in the ocean, making the water more acidic. Because ocean acidification happens particularly fast in cold water, that spells trouble for cold-water corals. How do they cope as their environment becomes warmer and more acidic?
Dressed in shark costumes, protesters marched to Maxim's Palace, a popular restaurant in Hong Kong, demanding an end to shark fin sales. Many species of shark are endangered. The restaurant said it has sharply reduced its shark fin sales volume in recent years.