Answer:
Where is the question photo
I think if the whale population decreased the surface fish populations would decline due to reduced populations of algae. This can be simply explained by the fact that, if the whale population is decreased, it means that the nitrogen rich feces that is supply nutrients to the algae would also decrease and therefore decrease the population of the algae and as a result the population of of the surface fish would also decline.
B. law of conservation of mass
This is why the total amount of and element before and after a chemical reaction is constant.
Answer:
I think it's b but good luck and nice profile pic :D