THE OCEAN: LIFE BELOW WATER AND WHY IT MATTERS - National ...Life under water encompasses vast, interconnected marine ecosystems that support an incredible diversity of plants and animals, from microscopic plankton to giant whales. These underwater worlds provide essential services, generating oxygen, regulating the global climate, and supplying food for billions of people. However, this vital aquatic life faces significant threats from human activities, including pollution, overfishing, and climate change, which damage marine habitats and jeopardize the planet's overall health and stability.