In general, there are two types of plants in the ocean: those that have roots attached to the bottom of the ocean and those that do not have roots and drift in the waters. Rooted plants live in only shallow waters because they need sufficient sunlight for photosynthesis. Sunlight does not reach the deeper parts of the ocean, which is why rooted plants cannot thrive in these regions.
Most of the oceanic surface waters have plants. Phytoplankton are the most common plants found in the ocean. These are single-celled plants that float throughout the surface waters. They need plenty of sunlight and nutrients from seawater to grow. Examples of phytoplankton are diatoms, which exist in a large number. A bucket of seawater can hold a million tiny diatoms. The presence of phytoplankton give a certain color to the sea. In cooler waters, where there are lots of nutrients from the sea floor due to storms, phytoplankton blooms give the sea vivid colors.
Seaweed, which is a type of phytoplankton, is commonly found floating on the surface of the ocean. It is harvested by people for food and material for housing, baskets and ropes. Seagrasses are rooted marine plants that live on the ocean floor. These flowering plants provide habitat for small fish and other marine life. Types of seagrasses include shoal grass, manatee grass and turtle grass.
Red algae live in warm tropical water, while coralline algae grow on rocks. The ocean also has an abundance of kelp beds that grow in cold temperate regions.