Anew company has just opened near the lake where this food chain takes place. the new company accidentally dumps in a poison which kills most of the algae. what would one expect to happen to the population of clams?

they will decrease due to lack of food

Explanation:

If you remove the algae they will decrease due to lack of food. The clams need the algae for food. if you remove that food source, the clam population will not have enough food to survive and thus will die.