The first link in ocean food chains, the primary producers , are often single-celled plants called phytoplankton . These plants, like those on land, require sunlight, nutrients, carbon dioxide gas, and water. Using the pigment chlorophyll , the phytoplankton harvest the sun's energy for use in photosynthesis in which they convert the carbon dioxide and water to high-energy organic compounds which form new plant material. This production of new plant material is primary production . A by-product of photosynthesis is oxygen gas which is required for respiration by plants and animals.
Respiration provides all organisms with the energy for their life processes.
The rate of primary production can be limited by the amount of sunlight, the nutrient supply and the stability of the surface water in an area. At polar latitudes the availability of sunlight limits the phytoplankton growth while in the tropics it is the nutrient supply which limits production. At temperate latitudes light, nutrients and water column stability vary with the seasons. Glossary Global Primary Production Where sunlight is not limiting, coastal waters are more productive than the open ocean because along the coasts rivers and land runoff supply nutrients. Also, tidal currents cause mixing and turbulence that bring nutrients from shallow depths to surface layers.