Algae have short life cycles, multiply rapidly, do not generate much biomass relative to their numbers, and are eaten rapidly by herbivores. At any given point in time, then, the standing crop of algae in an ocean is likely low, but the turnover rate can be high. Summary Organisms are characterized as autotrophs and heterotrophs. Autotrophs produce their own food by fixing energy through photosynthesis or, less commonly, chemosynthesis. Heterotrophs must feed on other organisms to obtain energy.
Primary production is the creation of new organic matter by plants and other autotrophs.
It can be measured per unit area for individual ecosystems or worldwide. Production also is measured per time unit, while standing crop biomass is the amount of plant matter at a given point in time. Production can be quantified by a simple process by which oxygen or carbon production is measured. Production varies among ecosystems, as well as over time within ecosystems. Rates of production are determined by such factors as climate and nutrient supply.