What is the most important animal in ocean?

The most important animal in the ocean is arguably the phytoplankton. Although very small in size, phytoplankton forms the base of the marine food chain on which everything else ultimately depends. They are microscopic, single-celled algae that drift in the water and use photosynthesis to convert sunlight, water, and carbon dioxide into food and oxygen. They have adapted to live in any body of water around the world, from the tropics to the polar ice caps. Phytoplankton provides much of the oxygen that we breathe and is an essential part of the Earth’s carbon cycle. They are also the foundation of the food web, providing sustenance to a vast array of marine life, including krill, fish, whales, birds, and even humans. Without phytoplankton, the ocean ecosystem would collapse and life on Earth would not be the same.