- If we assume a trophic efficiency of 10% , we can calculate how much primary production is required to support a particular fishery.
- For example tuna: tuna have a trophic level of 4, meaning they are secondary carnivores. For example a 175g can of tuna 175, 000g Carbon of phytoplankton is needed.
- Since humans often harvest secondary carnivores, such as fish, a lot more primary production is needed.
- The amount humans can take out of the ocean is largely dependent on the nitrogen and iron levels
2 ways in which productivity of the world's oceans for human food supply could be increased
- Increase the amount of nitrogen in the ocean - causing algal blooms
- Increase the amount of iron in the ocean - causing algal blooms
- Dedicate coastal areas to eutrophication and phytoplankton production
- Genetically engineer phytoplankton which need less nutrients/light