Beaked whales feed at various depths, but they defecate at the ocean's surface. nitrogen-rich whale feces deposited in surface waters supply nutrients for algae that are eaten by surface-dwelling fishes. predict what would happen if the whale population decreased?

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. 

Its either a) or b),wind and water erosion gradually widen the canyon