Consider this ecological pyramid found in the great lakes ecosystem. ecological pyramids are diagrams that are used to show how much energy, the number of organisms, or how much biomass may be found at each trophic level of all the food webs of a community. why are the autotrophs, in this case the algae, always placed at the base of the pyramid?

Autotrophs are organisms that uses light energy or energy stored in chemical compounds to make energy-rich compounds. The reason why autotrophs always occupy the lowest level of ecological pyramids is because they are the link between the sun's energy and the organisms that cannot manufucture their own food. Without an abudant amount of autotrophs we would be severely lacking in atmospheric oxygen and food. 

True, for example the gulf of mexico is surrounded by the us and spain& mexico.