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Geosciences LibreTexts

11.1: Primary Productivity

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  • The oceans encompass most of our planet therefore it makes sense that they represent the largest habitat on Earth. The oceans are home to a variety of different types of organisms. These organisms can be grouped into one of two groups: the autotrophs and the heterotrophs. Autotrophs are organisms that use inorganic compounds like carbon dioxide to produce organic products such as sugars and proteins. Heterotrophs on the other hand consume these organic products and release inorganic compounds as a by-product. An example of an autotroph would be phytoplankton who carry out photosynthesis. An example of a heterotroph would be a whale which consumes plankton and releases carbon dioxide as a by-product of cellular respiration. As you can see, there is a cyclic relationship between the biological processes of autotrophs and heterotrophs.

    Primary productivity is known as the synthesis of organic materials from inorganic substances. Two examples of primary productivity include photosynthesis, the synthesis of organic compounds using the sun as a primary source of energy, and chemosynthesis, the synthesis of organic compounds from inorganic molecules found in the environment. Chemosynthesis usually occurs in places where the sun is not present, such as the deep sea. Photosynthesis is more widely used by autotrophs to convert the sun’s energy into food energy.

    There are a variety of factors that determine the effectiveness of primary productivity. The amount of water, carbon dioxide, inorganic nutrients, and sunlight all play a major role in how productive primary producers are. However, water and carbon dioxide are not limiting factors in the ocean, as these are both abundant to the organisms. Primary producers, or autotrophs, are responsible for this phenomenon. Examples of primary producers include diatoms, dinoflagellates, and coccolithophores.

    Primary production is the most basic building block for the entire ecosystem and biosphere of not only the ocean but every environment in the work. It is the process in which autotrophs produce complex organic molecules through photosynthesis. During this process the autotrophs convert sunlight, carbon dioxide, and inorganic nutrients into organic material that are used as the basis for the rest of the food web. In the ocean the autotrophs which are responsible for primary production consist of phytoplankton, plants, and macroalgae since they all perform photosynthesis. All autotrophs performing photosynthesis do so through capturing solar energy in their pigmentation chlorophyll a. This pigment is especially effective in capturing light energy in the blue and red wavelengths of light.

    Primary production is often referred to in two ways: gross and net primary production. The entirety of the organic compounds produced by the primary producers is referred to as gross primary production. As with everything it is impossible to have 100% efficiency, the autotrophs require a part of the organic compounds that they produce for their own respiration processes. The amount of organic matter produced by the autotrophs that is not used by them and is available for consumption for heterotrophs represents the net primary production.