Biomass (ecology)

Biomass, in ecology, is the mass of living biological organisms in a given area or ecosystem at a given time. Biomass can refer to species biomass, which is the mass of one or more species, or to community biomass, which is the mass of all species in the community. It can include microorganisms, plants or animals. The mass can be expressed as the average mass per unit area, or as the total mass in the community. It might be measured in grams per square metre or tonnes per square kilometre, or it might be measured as the total mass present in a system such as a lake.

Just how biomass is measured depends on why it is being measured. Sometimes the biomass is regarded as the natural mass of organisms in situ, just as they are. For example, in a salmon fishery, the salmon biomass might be regarded as the total wet weight the salmon would have if they were taken out of the water. In other contexts, biomass can be measured in terms of the dried organic mass, so perhaps only 30% of the actual weight might count, the rest being water. For other purposes, only biological tissues count, and teeth, bones and shells are excluded. In stricter scientific applications, biomass is measured as the mass of organically bound carbon (C) that is present.

Ecological pyramids

An ecological pyramid is a graphical representation which shows, for a given ecosystem, the relationship between biomass or biological productivity and trophic levels.

• A biomass pyramid shows the amount of biomass at each trophic level.
• A productivity pyramid shows the production or turn-over in biomass.

Ecological pyramids provide a snapshot in time of an ecological community. They begin with producers on the bottom and proceed through the various trophic levels to the highest at the top. As the trophic level increases, the biomass decreases. That is, producers, such as grass, trees and scrubs, have a much higher biomass than animals that consume them, such as deer, zebras and insects. The level with the least biomass are the highest predators in the food chain, such as foxes and eagles.

Global biomass

The most successful animal species, in terms of biomass, is probably the Antarctic krill, Euphausia superba, with a biomass of about 500 million tons. However, as a group, the small aquatic crustaceans called copepods form the largest animal biomass on earth.

Humans comprise about 100 million tonnes of the Earth's biomass, domesticated animals about 700 million tonnes (1.0%), and crops about 2 billion tonnes. The total biomass of bacteria is estimated to equal that of plants .

Global primary production can be estimated from satellite observations. Satellites scan the normalised difference vegetation index (NDVI) over terrestrial habitats, and scan sea-surface chlorophyll levels over oceans. This results in 56.4 Gt C yr^-1 (53.8%), for terrestrial primary production, and 48.5 Gt C yr^-1 for oceanic primary production.. Thus, the total photoautotrophic primary production for the Earth is about 104.9 Gt C yr^-1 This translates to about 426 g C m^-2 yr^-1 for land production (excluding areas with permanent ice cover), and 140 g C m^-2 yr^-1 for the oceans.

However, there is a much more significant difference in standing stocks - while accounting for almost half of total production, oceanic autotrophs account for only about 0.2% of the total biomass.

See also

• Biota (ecology)
• Lake Pohjalampi (in Finland)
• Natural organic matter (NOM)
• Water mass

References

External links

• Counting bacteria