Whale Fall: Food Bonanza on the Ocean Floor
The pygmy blue whale is a subspecies of the blue whale and is found in the Indian and Pacific Ocean. At 70-80 feet in length, it is the smallest of all blue whales. Photo: Umeed Mistry
Published on Roundglass Sustain - December 2020
In October 2019, scientists using a remotely operated vehicle to explore the seabed off central California’s coast came upon an unusual scene 3,240 m below the surface: a motley crew of deep-sea dwellers feasting on a whale carcass. Octopuses, eel pouts, and colonies of Osedax worms (sometimes known as bone-eating snot flower worms) were eating through the four-to-five-metre-long body. The scientists of the Exploration Vessel Nautilus had discovered one of the marine world’s most unique ecological communities — a whale fall.
When whales die, their bodies either wash ashore or plummet to the depths of the ocean; in the latter situation the carcass is known as “whale fall”. These corpses are food bonanza on oceans floors where nutrients often only come from organic matter sinking from the surface (like animal poop or decaying corpses of small creatures). According to the authors of a 2016 article entitled “Deep-sea whale fall fauna from the Atlantic resembles that of the Pacific Ocean” published in Nature, “Whale carcasses are considered the largest organic inputs reaching the deep ocean floor in a single event.”
Video: EV Nautilus
What’s fascinating about these remains is the energy-rich habitats they create and how long they last. “Whale falls are interesting to study as they form an ecosystem in the oceans from scratch — everything from microorganisms to large marine megafauna depend on them as time passes,” said ecologist Dipani Sutaria. “Evolutionary processes happen here, new species might also arise, and even reefs may form around the skeleton.” Research has shown that whale falls can last from a few years to decades, given how the body degrades over multiple stages.
As the carcass decomposes, it supports a succession of marine life or communities. The first stage of what is called “whale-fall community succession” is the mobile-scavenger stage. This sees the likes of hagfish and sleeper sharks tearing away at the carcass’s flesh. Next is the enrichment-opportunist stage, where the bones and nearby organically enriched seabed are taken over by crustaceans, molluscs, and polychaete worms. A 2002 article on whale falls from the Monterey Bay Aquarium Research Institute states that “Worms often carpet the seabed at densities of up to 45,000 animals per square metre — higher densities than in any other deep-sea environment.” This is followed by the sulfophilic stage, during which bacteria break down fats in the bones and produce hydrogen sulfide as a result. That gas, in turn, supports other microbes and bacteria. “You get these thick bacterial mats, that grow all over the bones, and are white and yellow and orange and sort of can glow,” deep-sea biologist Diva Amon told NPR in 2019.
When a whale dies and sinks to the bottom of the ocean floor, it sparks a series of processes that generate an entire ecosystem, and support multiple creatures living around the ocean floor. The Bryde's whale’s skeleton was photographed in the South Andaman Sea in Thailand. Photo: Sineenuch J/Shutterstock
In addition to being a food source, whale falls also support unique creatures. A 2015 study entitled “Whale-Fall Ecosystems: Recent Insights into Ecology, Paleoecology, and Evolution” states that “a total of 129 newly described and putative new species from seven phyla have been collected on whale remains, of which 37 have been formally described and 102 are potentially whale-fall specialists.”
One such creature is the bone-eating Osedax worm, various species of which have been found on whale falls around the world. As per the 2015 study mentioned earlier, the worms are characterised by “a bizarre palm-tree like morphology, with a crown of reddish palps/gills, a mucus-clad trunk, and bulbous green or yellow root-like structures (large ovisacs) that penetrate cavities in bones.” They burrow into bones with their roots and digest fats from the marrow using bacteria in their tissue.
According to the 2016 Nature report, natural whale falls are likely to occur along migratory routes and in breeding and feeding areas. To allow for better research, scientists have resorted to intentionally sinking carcasses that wash ashore. An example of this is Rosebud, a sixty-foot, twenty-three-tonne whale that was sunk off the coast of San Diego, California, using “five tons of rusty chains” and “two tons of iron shackles,” as described in a 2019 New Yorker story.
What we know about whale falls so far is just part of the story; there is a lot that remains unknown. These marine giants continue to intrigue researchers, in life and in death.