A whale fall occurs when the body of a cetacean falls to the ocean floor. This creates a complex and localized ecosystem for a huge variety of animals and other organisms. The depth of the ocean creates the perfect conditions for this, due to enormous pressure and cold temperatures which prevent the body from decomposing too quickly. A whale fall has three main stages of activity, and a single whale can provide shelter and food for microorganisms for decades.
The first phase occurs just after the fall, when scavengers locate the carcass. These mobile scavengers can include hagfish, ratfish, sharks, crabs, and amphipods. They feed off of the remains until they can no longer gain anything from it. This phase lasts for days or months, depending on the depth and the size of the body.
The second phase is known as the enrichment opportunist phase. Smaller animals like worms, mollusks, and a variety of crustaceans feed on organic material in the bones and leftover blubber. The nutrient-enriched sediment that surrounds the whale after it falls also makes a great place for these species to burrow. Many of these species appear to be unique to deep-sea whale falls. After a year or two the majority of the easily digestible organic material has been consumed. Sulfur-reducing bacteria can continue to feed on fats and oils inside of the whale bones, which gradually releases hydrogen sulfide. This provides the basis for the third and final stage.
The last stage is called the sulfophilic (sulfur-loving) stage. This stage can last decades – at least one whale fall community has lasted over 50 years. At this point, only the skeleton of the whale remains. Bacteria begins to break down fats and oils inside of the whale bones, creating sulfur in the process. This in turn attracts more bacteria to the whale fall, along with a large number of highly diverse and rare species including different mussels, snails, worms, and more.
The diversity of species that are found in the final stage is larger than any other known community on the deep seafloor. Up to 190 different species of macroscopic animals have been found on a single skeleton! Most of them have specifically adapted to make the most of whale-falls as a food source and substrate.
While it is always sad when a whale dies, it is an amazing and beautiful part of nature that allows it to provide life on an otherwise barren seafloor. There are so many species that depend on whale falls to thrive!
Video credits: Sharon Shattuck & Flora Lichtman for Sweet Fern Productions