The term for ocean plants that produce oxygen is phytoplankton. These microscopic organisms are vital to Earth's ecosystems, as they perform photosynthesis and convert sunlight, carbon dioxide, and water into oxygen and organic matter. Phytoplankton constitutes the base of the marine food web, serving as a primary food source for various marine animals, including zooplankton, small fish, and larger marine creatures. They thrive in sunlit, nutrient-rich surface waters and are responsible for producing approximately 50% of the global oxygen supply, making them essential for sustaining life on our planet and contributing to global carbon cycling.