This video is called Whale Fall (after life of a whale) and was produced by Sharon Shattuck and Flora Lichtman of Sweet Fern Productions. A whale fall is the name given to what happens a whale dies, and its carcass sinks to the ocean floor. All the stored energy in the whale’s body is released.
Countless organisms, hagfish being the most obvious, feed on its remains for decades afterwards. Some species only live on whale carcasses, and when they spawn it is a lottery whether their offspring will find another dead whale to settle on. This is a beautiful illustration of the (sorry to be cheesy) circle of life.