Which organisms is a producer in a marine ecosystem?

In a marine ecosystem, phytoplankton are the primary producers. These microscopic plants, including various types of algae, use photosynthesis to convert sunlight into energy, forming the foundation of the food web. They produce oxygen and serve as a crucial food source for a wide range of marine organisms, from small zooplankton to larger fish and whales. Additionally, larger seaweeds and seagrasses also contribute to primary production in these environments.