why are whales important to the ecosystem?

Every part of an ecosystem is at least partially dependant on the other. Every animal plays a role to keep it balanced. Greater species diversity ensures sustainability for all life forms, and healthy ecosystems can better withstand disasters. The whales have a significant role in the global marine ecosystems and declines in whale populations can reasonably be expected to impact many other marine species. Whales play a very important role in the balance of nature. Whales help to keep the populations of their prey species in check

If they were to disappear, their preys would increase dramatically in number, thus overeating other preys, so on and so forth to the point that whole ecological balance of the oceans could be severely affected.