What is the primary role of phytoplankton in marine ecosystems?

Phytoplankton play a crucial role in marine ecosystems primarily as producers. They are microscopic organisms that perform photosynthesis, using sunlight to convert carbon dioxide and nutrients into organic materials. This process not only sustains phytoplankton themselves but also forms the foundation of the marine food web, providing energy and organic material for a wide range of marine organisms, including zooplankton, fish, and larger marine mammals.

As the primary source of energy in aquatic ecosystems, phytoplankton contribute to approximately half of the Earth's total oxygen production, making their role even more significant in supporting both marine life and global climate regulation. Their abundance and productivity are vital for maintaining the health and balance of marine environments. Other roles, such as decomposers or scavengers, are fulfilled by different organisms in the ecosystem, which highlight the unique and essential function that phytoplankton serve as primary producers.