When a blue whale, the largest animal on Earth, dies, its massive body embarks on a fascinating journey of decay and renewal, particularly if it dies in the ocean. This process, known as a whale fall, creates a unique ecosystem on the ocean floor, supporting a variety of deep-sea creatures for decades.

Blue Whale Dies

Sinking and Scavenging

Unlike cartilaginous fish, a whale’s body will float for a period due to gas buildup in its stomach. During this time, scavengers like sharks and seabirds will feed on the carcass. Eventually, however, the whale will sink, often to depths of over 1,000 meters, becoming a whale fall on the seabed.

The decomposition of a whale fall proceeds in stages:

  • Mobile-Scavenger Stage: Large scavengers such as hagfish, sleeper sharks, crabs, and lobsters consume the soft tissue, blubber, and muscles of the whale, reducing the carcass to bones within months. A single whale can sustain these animals for up to two years.
  • Enrichment-Opportunist Stage: Once the soft tissue is gone, sea snails, bristle worms, and shrimp consume any remaining scraps and organic matter, while polychaete worms help reduce the carcass to bare bones. This stage also lasts for around two years.
  • Sulphophilic Stage: This final stage is characterised by bacteria that consume the fat inside the whale bones, producing hydrogen sulphide. This stage can last from 10 to 50 years.

A Deep-Sea Ecosystem

The whale skeleton itself becomes a substrate for various organisms, creating a localized ecosystem. The organic fragments from the decaying whale enrich the surrounding sediments, providing a food source for more than a year.

Chemoautotrophic organisms thrive during the sulphophilic stage by converting the hydrogen sulphide released by bacteria into usable energy. These organisms include molluscs and tube worms and are similar to those found at cold seeps and hydrothermal vents. The whale fall provides a unique stepping stone for these specialised animals to spread across the ocean floor.

The Role of Zombie Worms

Among the strangest inhabitants of a whale fall are Osedax worms, also known as “zombie worms” or “bone worms”. These invertebrates bore into the bones, using specialised methods to break down elements like collagen and fat. They have root systems filled with bacteria that help them digest the whale’s bone fat. The worms also push oxygen into the bones, speeding up decay. Osedax males are dwarfed by the females and live on the outside of their tubes, fertilising eggs as they are released. The Osedax larvae can then settle on nearby bones or drift to another whale carcass. These worms can spend up to 10 years harvesting the remains of a whale.

A Cycle of Life

Whale falls provide energy and nutrients to the deep-sea food chain. The amount of carbon tied up in a whale carcass is substantial, equivalent to the amount that falls to 10 square kilometers of seabed in 150 years. This is a significant contribution in the otherwise food-scarce environment of the deep ocean. A single whale carcass can support over 12,000 individual organisms from an estimated 43 different species.

Although the death of a whale might seem tragic, the resulting whale fall demonstrates the vital role these giants play in the marine ecosystem, even in death. They become a source of life for hundreds of marine animals for up to 50 years.

It is important to note that not all whales sink to the ocean floor after death. Sometimes, they get beached. In such cases, the whale can become a hazard if not disposed of properly.

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