Plants are known as primary producers, because they take energy from the sun and, through a process known as photosynthesis, create sugars, which translate into "fuel" for living things. On land, plants tend to be large and quite easily noticed. Trees, for example, can grow to heights exceeding 300 feet. In the sea, on the other hand, marine plants tend to be small, sometimes too small to distinguish with the naked eye.

There are, however, marine plants that grow large, such as the kelp found on the west coast of the U.S. Some can resemble terrestrial plants with structures that appear similar to leaves, including caulerpa, sometimes known as feather algae, and many other species of sea weed. Many marine plants (algae) are microscopic and occur in large blooms, providing a basic food source at the very bottom of the food chain. Disruptions in these blooms of marine algae can affect animals all the way at the top of the food chain.