Final answer:
The trophic level with the smallest biomass is typically the quaternary consumers, as depicted in an ecological pyramid which shows a decrease in biomass from lower to higher trophic levels.
Step-by-step explanation:
In a food chain, the trophic level that supports the smallest biomass of organisms is typically the highest level: the quaternary consumers. These are organisms that feed on tertiary consumers, which in turn feed on secondary consumers and so forth down to producers at the base of the food chain.
An ecological pyramid illustrates the decrease in available energy, number of organisms, and biomass as one moves from lower to higher trophic levels. With the energy transfer being inefficient (only about 10 percent of the energy is transferred from one trophic level to the next), most energy is lost at each level, resulting in a smaller biomass at higher levels.
This is why apex predators, such as the Chinook salmon in Lake Ontario, have a much lower biomass compared to the producers at the base of the pyramid.