What type of organism in the ocean makes up most of this biomass?

In the ocean, phytoplankton are the primary organisms that make up most of the biomass. These microscopic plants, which include various types of algae, play a crucial role in the marine food web and are responsible for producing a significant portion of the Earth's oxygen through photosynthesis. Their abundance and efficiency in converting sunlight into energy contribute to their dominance in oceanic biomass.