What Is Primary Productivity? A Definition and Explanation

What Is Primary Productivity? A Definition and Explanation
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Primary Production

To adequately define primary production we must first have a basic understanding of the food chain. All organisms feed off from the organisms below them on the food chain. The base, the very first level of organism has to feed on something too. These organisms create their food through the process of photosynthesis or chemosynthesis. This is what a primary producer does, makes its food from inorganic materials.

In the ocean, this is done in one of two ways in one of two places. Photosynthesis is performed by phytoplankton on or near the surface of the sea. This process takes carbon dioxide and water and combines them with the help of the energy contained in sunlight creates a monosaccharide and oxygen. We often hear about photosynthesis as a way to produce oxygen but very rarely do we talk about this equally essential product, the building block of the food chain.

CO2 + H2O + light CH2O + O2

The other process, chemosynthesis, doesn’t get as much press as photosynthesis because it only happens deep in the ocean around thermal vents. Here there is no sunlight, so organisms adapted to into lithotropes able to transform carbon dioxide, oxygen and hydrogen sulfide and creates a monosaccharide, sulfur and water.

CO2 + O2 + 4 H2S CH2O + 4 S + 3 H2O

Both processes create the basic organic unit of energy, monosaccharide (CH2O). This energy is then either used by the creating organism or consumed by a larger organism, further up on the food chain. Now that we’ve answered the question What is primary productivity? Who are the producers?

Primary Producers

Primary producers, or autotrophs, in the ocean are either plants (near the shoreline) phytoplankton (at the surface of the ocean), lithotropes (near deep ocean thermal vents) or bacteria.

Plants – Most plant-based photosynthesis is limited to various grasses in the littoral region of the ocean where plants can root and still reach a height that they can take advantage of the photons in sunlight. There are some notable exceptions including the free-floating Sargassum, which floats out away from the littoral zones. Root bound and free-floating plants contribute a tiny amount to the total monosaccharide and oxygen production of the ocean.


Phytoplankton is a term for all of the small photosynthetic organisms that populate the region in the upper level of the ocean. Several different types of autotrophs often inhabit the same area creating a base area for zooplankton to feed. The exception to this rule is Cyanobacteria, which is often the only autotroph in its area.

Prokaryotic Bacteria -

  • Lithotropes are symbiotic bacteria that live in the bodies of tubeworms near hydrothermal vents in the ocean floor. The worms filter hydrogen sulfide laced water through their digestive tract where the lithotropes create monosaccharides for both the bacteria and host to feed on.
  • Cyanobacteria, or blue-green algae, are the largest producers of primary materials in the world. These bacteria, under the right conditions, multiply rapidly and can cause large-scale “blooms.” These blooms are often the result of a high concentration of available iron and sunlight.

Eukaryotic Algae -

  • Red Algae is a group of 5,000 to 6,000 different variations. Each of these is similar in pigmentation and has a closed membrane that contains all of the parts of the plant. This is the major difference between Prokaryotic and Eukaryotic algae, the presence of a membrane.
  • Green Algae is also a group of about 6,000 individual types of algae. Most are single cells but some form colonies, long filaments, or macroscopic seaweeds.
  • Dinoflagellates are flagellate protists or single-celled plants with whip-like structures that allow for stabilizing themselves in the water. Not all dinoflagellates are primary producers but those that are, usually have two to four flagella.
  • Coccolithophore are algae with the ability to swim. These calcium covered single-celled organisms straddle the line between plant and animal and usually travel as large clusters although they can maneuver individually.
  • Diatoms are one of the largest groups of algae. There are over 100,000 variations, but all have similar lifestyles. They group together and under favorable conditions reproduce at an astronomical rate, often dominating an entire region of phytoplankton. Once the nutrients level off or decrease the diatoms, lose the ability to maintain their buoyancy and fall out of the upper level of the ocean.

Why Primary Producers Are Important

Primary producers are the base level of the food chain. They are the only organisms on the planet that can create their own food from inorganic materials. Phytoplankton, as a primary ocean producer, is fed on by zooplankton, which is fed on by small crustaceans and fishes, which are in turn fed on by larger fishes and so on and so forth.

Without the phytoplankton, there would be no food for zooplankton and thus no food for creatures further up the food chain. All life in the ocean would starve to death if there were a sudden removal of all primary producers.