7.1 Primary Production
is the creation of new organic matter from inorganic substrates, and it is this organic matter that serves as the base of the food web for most marine consumers. Primary production generally refers to the process of , or the utilization of light energy to produce chemical fuels that is undertaken by plants and algae according to the reaction:
6CO2 + 6H2O → C6H12O6 + 6O2
Here, powered by light energy, carbon dioxide and water combine to produce glucose and oxygen. However, primary production is also carried out by bacteria in the absence of light through . Instead of light providing the energy for the reaction, the energy comes from the oxidation of inorganic materials, such as hydrogen sulfide (see section 4.11 on ). Here we will concentrate on photosynthesis because it plays a much larger role in total oceanic productivity than chemosynthesis.
The organisms responsible for oceanic primary production include a wide diversity of marine plants and algae. While many people may be more familiar with the larger seagrasses and macroalgae (seaweeds), by far the greatest amount of photosynthesis in the ocean comes from microscopic algae, the . The term “” refers to organisms that drift with the currents, and the phytoplankton are the free-floating algae that undergo photosynthesis (contrast this with the , who are the drifting animals). In section 7.2 we will take a closer look at the organisms responsible for oceanic primary production.
The total amount of organic material created by the producers is called the , or total production. However, the primary producers consume a portion of this organic matter themselves through respiration, so the total amount that is left to support the consumers in the ocean is called (gross productivity – respiration). Gross production can be divided into two components, new production and regenerated production. is supported by brought in from outside of the local ecosystem through processes such as or ocean currents. results from the recycling of nutrients within an ecosystem.
Overall, marine productivity is similar to terrestrial production. Marine net production is about 35-50 billion metric tons per year, while terrestrial production reaches 50-70 billion tons per year. However, the biomass responsible for that production in the ocean is about 1-2 billion metric tons, compared to 600-1000 billion metric tons of biomass in terrestrial systems. So the oceans are producing almost as much organic material as terrestrial producers, but are doing it from only a fraction of the amount of producer biomass. One reason for this discrepancy is that the phytoplankton are constantly being consumed, while much of the terrestrial biomass is much longer-lived than the plankton.
the synthesis of organic compounds from aqueous carbon dioxide by plants, algae, and bacteria (7.1)
the production of organic compounds from carbon dioxide and water, using sunlight as an energy source (5.5)
the creation of organic compounds using the energy from inorganic chemical reactions (4.11)
area of the seafloor where superheated water seeps out of the crust (4.11)
drifting, usually single-celled algae that undergo photosynthesis (7.1)
an organism that cannot swim effectively, so it drifts with the currents (7.1)
small, drifting carnivorous organisms (7.1)
the total amount of organic material created by primary producers (7.1)
total primary production minus the organic compounds used up by respiration by the producers (7.1)
primary production supported by nutrients brought in from outside of the local ecosystem (7.1)
in the context of primary production, substances required by photosynthetic organisms to undergo growth and reproduction (5.6)
process by which deeper water is brought to the surface (9.5)
primary production resulting from the recycling of nutrients within an ecosystem (7.1)