Phytoplankoton are the primary energy producers of the ocean ecosystem. They create the energy from the light sources such as sun. They convert the obtained light energy into carbohydrates by the process of photosynthesis. The energy produced by the phytoplankton is not consumed by it. These are the important food sources for the aquatic animals in order to support the food chain. These are considered as the foundation of the aquatic food web. These phytoplanktons even cause death of the organisms. When the phytoplankton die it sinks to the bottom of the water body and the bacteria which feed on the dead phytoplankton release oxygen making the marine life suffocating. These phytoplanktons produce chemical energy from sun light. These produce carbohydrates by utilising carbon dioxide from atmosphere resulting in water and oxygen as the end product.
Therefore, Phytoplanktons act as PRODUCERS in an ocean ecosystem.