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primary productivity
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phytoplankton bloom
phytoplankton bloom
phytoplankton bloom Atlantic Ocean currents collide off the coast of Argentina, causing huge phytoplankton blooms (green and blue swirls). Phytoplankton blooms makes up much of the ocean's primary productivity in Earth's oceans.

primary productivity

biology
Also known as: primary production
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primary productivity, in ecology, the rate at which energy is converted to organic substances by photosynthetic producers (photoautotrophs), which obtain energy and nutrients by harnessing sunlight, and chemosynthetic producers (chemoautotrophs), which obtain chemical energy through oxidation. Nearly all of Earth’s primary productivity is generated by photoautotrophs.

Calculating primary productivity

The total amount of biological productivity in a region or ecosystem is called the gross primary productivity. A certain amount of organic material is used to sustain the life of producers (or autotrophs) in a food chain, and what remains is the net primary productivity, which can be used by consumers (or heterotrophs, which are made up of herbivores and carnivores in each environment). Primary productivity is usually determined by measuring the uptake of carbon dioxide or the output of oxygen. Production rates are usually expressed as grams of organic carbon per unit area per unit time.

Types of primary producers

In marine environments, the two principal categories of producers are pelagic phytoplankton, which float freely in the ocean, and benthic algae, which live at or near the ocean’s floor. In terrestrial environments, primary productivity is generated by trees and other land plants (including planted crops). Most primary producers require nitrogen and phosphorus—which are available as dissolved nutrients in the soil, lakes, and rivers and in the oceans as nitrate, nitrite, ammonia, and phosphorus. The abundances of these molecules and the intensity and quality of light exert a major influence on rates of production.

The annual productivity of the entire ocean is estimated to be approximately 50 × 1015 grams (50 × 109 metric tons) of carbon per year, which is about half of the global total. Most primary productivity in the oceans is carried out by free-floating phytoplankton in the open ocean rather than by bottom-dwelling (benthic) plants, with chemoautotrophs contributing smaller amounts as producers in deep-sea-vent habitats. Benthic plants grow only on the fringe of the world’s oceans and are estimated to produce only 5 to 10 percent of the total marine plant material in a year.

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ecosystem
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Yamal Peninsula
How an ecosystem works: Producers, herbivores, and carnivores
How an ecosystem works
marine food chain terrestrial food chain food web energy pyramid measuring biodiversity ecosystem energy transfer scale in ecological studies
What is biodiversity, and why is it important?
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Chutes d'Ekom - a waterfall on the Nkam river in the rainforest near Melong, in the western highlands of Cameroon in Africa.
Ecosystems
Yamal Peninsula
Yamal Peninsula Tundra and lakes during summer in the Yamal Peninsula of Siberia, Russia. Tundra ecosystems are found primarily in the Low Arctic region of North America and Eurasia. Most regions—with the exception of rock outcrops, dry ridge tops, and river gravel bars—are fully vegetated, primarily by dwarf shrubs, lichens, and mosses.

ecosystem

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Key People:
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ecosystem, the complex of living organisms, their physical environment, and all their interrelationships in a particular unit of space.

A brief treatment of ecosystems follows. For full treatment, see biosphere.

An ecosystem can be categorized into its abiotic constituents, including minerals, climate, soil, water, sunlight, and all other nonliving elements, and its biotic constituents, consisting of all its living members. Linking these constituents together are two major forces: the flow of energy through the ecosystem and the cycling of nutrients within the ecosystem. Ecosystems vary in size: some are small enough to be contained within single water droplets while others are large enough to encompass entire landscapes and regions (see biome).

(Read E.O. Wilson’s Britannica essay on mass extinction.)

Energy flow

How an ecosystem works: Producers, herbivores, and carnivores
How an ecosystem works: Producers, herbivores, and carnivoresUnderstanding energy flow in ecosystems.
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The fundamental source of energy in almost all ecosystems is radiant energy from the Sun. The energy of sunlight is used by the ecosystem’s autotrophic, or self-sustaining, organisms (that is, those that can make their own food). Consisting largely of green vegetation, these organisms are capable of photosynthesis—i.e., they can use the energy of sunlight to convert carbon dioxide and water into simple, energy-rich carbohydrates. The autotrophs use the energy stored within the simple carbohydrates to produce the more complex organic compounds, such as proteins, lipids, and starches, that maintain the organisms’ life processes. The autotrophic segment of the ecosystem is commonly referred to as the producer level.

Chutes d'Ekom - a waterfall on the Nkam river in the rainforest near Melong, in the western highlands of Cameroon in Africa.
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Ecosystems
How an ecosystem works
How an ecosystem worksExplore the different types of organisms that form a forest ecosystem in this video.
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Organic matter generated by autotrophs directly or indirectly sustains heterotrophic organisms. Heterotrophs are the consumers of the ecosystem; they cannot make their own food. They use, rearrange, and ultimately decompose the complex organic materials built up by the autotrophs. All animals and fungi are heterotrophs, as are most bacteria and many other microorganisms.

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