The oceans are home to awe-inspiring biodiversity, much of which is yet to be discovered. They also play a crucial role in our fight against climate change and are essential for the survival of millions of people around the world. And yet, we often forget about their importance and rarely realize how seriously they are threatened by human activity. Francois Simard is Deputy Head of IUCN’s Global Marine Programme. He explains the difference between marine ecosystems and terrestrial ecosystems.