Extremely rare footage of a whale fall in deep, deep sea.

From YT:

Footage of the decomposition of a large whale carcass in the deep sea. Notice the successional changes in the community that is supported by this massive input of nutrients.

From WIKI:

Whale fall is the term used for a whale carcass that has fallen to the ocean floor.[1] Whale falls were first observed in the 1980s, with the advent of deep-sea robotic exploration.[2]

When a whale dies in shallow water, its carcass is typically devoured by scavengers over a relatively short period of time—within several months. However, in deeper water (depths of 2,000 m/6,600 ft or greater), fewer scavenger species exist, and the carcass can provide sustenance for a complex localized ecosystem over periods of decades.[3]

Some of the organisms that have been observed at whale falls are squat lobsters, Osedax (bone-eating worms), crabs, sea cucumbers, octopuses, clams, and even deep-sea sleeper sharks. Whale falls are often inhabited by large colonies of tubeworms. Over 30 previously unknown species have been discovered at whale falls.[citation needed]

A whale fall was first observed by marine biologists in 1987, discovered accidentally by the submersible Alvin. Whale falls have since been found by other scientists, and by military submarines. They can be found by using side-scan sonar to examine the ocean floor for large aggregations of matter.

Some scientists speculate that certain deep-sea species may use whale falls as stepping-stones to extend their range and colonize other ecosystems, such as hydrothermal vents and cold seeps. Given that whale deaths occur at locations that are largely random, carcasses are believed to exist at many locations on the seabed, like oases in the nutrient-poor abyssal plain, with average spacings estimated at 25 km (16 mi). Marine biologists sometimes transport dead whales that have washed up on coastlines, towing them offshore to create a whale fall at a known location that can then be studied over a long period of time.

Similar ecosystems exist when other large volumes of nutrient-rich material fall to the sea floor. Sunken beds of kelp create kelp falls, and large trees can sink to create wood falls.