There are thousands of different species of ocean plant life, including phytoplankton, algae, kelp and seagrasses. There are over 130,000 species of algae alone, but the most common forms are red and brown algae. Red algae is what is commonly seen on coral reefs, and brown algae is considered the most complex form of algae.
Although similar in name, seagrasses are different than seaweed, and they are flowers that grow entirely submerged in the ocean. Kelp is a form of brown algae and can be found in cold temperate waters. Phytoplankton are a single-celled species of microalgae that can be found across the globe and serve as a primary food source for many forms of marine life.