The deep ocean biome consists of the lowest areas of the ocean. Because sunlight is unable to penetrate water at this depth, this deprives plants from their traditional source of nutrition. Plants use a process called photosynthesis to convert sunlight into energy. As a result, plants that live in the deep ocean biome may have different appearances compared to a land-based plant. However, some plants do manage to make the deep ocean their home.
Red algae are a collection of plant species that exist in the ocean. These algae are typically multicellular plants, and they too receive energy from photosynthesis. However, red algae contain special pigments called phycoerythrins, which absorb blue light and reflect red light. Blue wavelengths of light penetrate the ocean farther than other types of light, allowing red algae to produce energy in much deeper waters than most other plants.
Sea grasses are a type of flowering aquatic plants that blanket many seafloors. These plants typically exist in shallow, warmer waters where they can absorb the sunlight they need for energy. However, in specific areas of the ocean, specifically around the Great Barrier Reef near Australia, various species of sea grass have been observed living in waters as deep as 60m -- perhaps possible in the Great Barrier Reef because of the particularly clear water that allows sunlight to penetrate much deeper than normal.
Seaweeds like kelp anchor themselves to the ocean floor and grow large leaves that can reach the surface of the ocean. Kelp typically grow in shallower waters but some research has suggested that groups of kelp, called kelp forests, have grown to depths of more than 60m. Kelp forests may exist that originate in even deeper depths.
Plankton are microscopic creatures that may be either plants or animals. Plant plankton are also typically known as phytoplankton. These phytoplankton need sunlight in order to generate food production, and so rarely exist alive in the deep ocean biome. However, when phytoplankton die, they float down to the deep ocean. Phytoplankton exist in such numbers that dead phytoplankton form an important source of nutrients to fish and other animals that live in the deep ocean.