When you decrease the pH in the simulation, the ocean’s acidity increases. What do you expect to happen over time to the population of the corals, algae, and fish in the coral reef as the pH of the ocean decreases?

With decrease in pH of ocean water, the survival rate of corals, algae, and fish in coral reef reduces.

Explanation:

Coral reefs find difficulty in living in acidic ocean water. It is so because the coral’s shell that is made up of calcium carbonate is unable to sustain in acidic environment.  

Not only this the skeleton of snails, clams, algae , fish etc is also made up of calcium carbonate. Increased acidity leads to death of these species.  

Thus, the lower is the pH of ocean water, the higher is its acidity and hence the lower is the probability of survival of corals, algae, and fish in the coral reef