Mako sharks weigh about 1000 pounds when they reach maturity. suppose that in a gulf near south america, the following food chain exists

diatom algae -> sardines -> blackfin tuna -> mako shark

a plankton tow estimates that there are about 100 million pounds of diatoms in the gulf. how many adult mako sharks can the gulf support?

The correct answer is 100 adult sharks.

Approximately 10% of the energy is stored in the organisms of each trophic level is available as a food for the next trophic level. Rest of the energy is used by the organism itself for the metabolic function. In this question 100 million pounds of diatoms is present in gulf, out of which 10 million pounds of diatoms available for sardines and 1 million pound is available at black fin tuna and 0.1 million pound is available for mako shark. Each adult mako shark weighs 1000 pounds. Therefore, 0.1 million pound of diatoms can supports 0.1 million divided by 1000 is equals to 100 sharks.