- Phytoplankton: These are microscopic algae that float in the water column and use sunlight to photosynthesize. They are the foundation of the marine food chain and produce about 50% of the oxygen in the Earth's atmosphere.
- Macroalgae: These are larger algae that attach to the sea floor or other surfaces. They include kelp, seaweed, and rockweed.
- Benthic microalgae: These are microscopic algae that live on the sea floor or other surfaces. They are important in nutrient cycling and provide food for bottom-dwelling organisms.
- Bacteria and archaea: These microscopic organisms use chemosynthesis to produce organic matter from inorganic compounds. They are found in extreme environments, such as hydrothermal vents and cold seeps.