Factors that limit the type of life forms able to live in an ocean environment include temperature, sunlight, pressure, oxygen concentration and nutrient availability. Because of its many varied attributes, the ocean offers a unique home to aquatic life.
The various organisms living in the sea are suitably adapted to temperatures at differing depths. Because sunlight can penetrate water to only about 100 feet, water temperature falls with the ocean's floor. Sunlight is not only important to water temperature, but is necessary for the production of oxygen and other important substances. The weight of the water exerting pressure on life forms in the ocean increases with depth, limiting life at increasing depths. Finally, supplies of nutrients often run short in different regions, with nitrogen being the primary limiting nutrient to saltwater life.