Phytoplankton play a crucial ecological role in marine ecosystems as they are foundational to the marine food web. These microscopic organisms are responsible for producing a significant portion of the world's oxygen through photosynthesis and are primary producers that support fish and other marine life. They act as the base of the food chain, supporting various trophic levels from zooplankton to larger predators. Healthy populations of phytoplankton are essential for maintaining ocean health and stability, impacting global biochemical cycles and serving as indicators of ecosystem changes.