Whale Falls: Carbon and Life in the Deep Sea

What a whale's death delivers to the deep: tens of tons of organic "gift"

The deep sea is a place with little food

Sunlight does not reach below about 1,000 m. Organic matter made by phytoplankton through photosynthesis is eaten or decomposed as it sinks, and very little reaches the seafloor. These sinking particles are called "marine snow" and are the everyday food of deep-sea animals.

Into this quiet dining room, tens of tons of food can suddenly drop: the carcass of a large whale. Adult large whales are reported to weigh 30–160 t (Smith & Baco, 2003), most of it fat, muscle and bone. Where a whale sinks, an ecosystem unlike the surrounding seafloor arises.

The discovery of whale-fall communities

This ecosystem became a subject of science in the late 1980s. In the Santa Catalina Basin off California (about 1,240 m deep), the submersible Alvin found a baleen whale carcass and the animals swarming on it (according to Scientific American and other accounts). Surveys by submersibles and robots followed, and communities that depend on whale carcasses came to be called "whale-fall communities".

For the basic succession, see our article What is a whale-fall community?. Here we go a step further, from research in Japanese waters, the evolution of bone-eating worms, and the history of carbon and whaling.

The three stages: a chain of life as the main players change

Whale-fall communities are generally said to pass through three stages. Their length varies greatly with carcass size, depth, water temperature and surroundings.

Main players and timescale of each stage

In the first stage, hagfish and sharks strip soft tissue; consumption of 40–60 kg per day has been reported, and most soft tissue disappears within months to a little over a year. In the second stage, polychaetes and crustaceans gather in the organically enriched sediment. The next, third stage is the greatest feature of whale-fall communities.

Lipids inside the bone power the third stage

Whale bones contain large amounts of lipids. When bacteria break them down on the oxygen-poor seafloor, hydrogen sulfide is produced. It is poison to many animals, but a feast for chemosynthetic bacteria, which use it as an energy source to make organic matter. Clams and worms that host these bacteria gather, and a food web independent of sunlight lasts for decades.

Hydrothermal vents and cold seeps are likewise chemosynthesis-based. Researchers discuss whether whale falls act as "stepping stones" that share animals with such places.

Bone-eating worms: the discovery and evolution of Osedax

An accidental discovery in Monterey Bay

In February 2002, researchers at the Monterey Bay Aquarium Research Institute (MBARI) used the ROV Tiburon to examine a gray whale carcass at about 2,893 m in Monterey Canyon. They found the bones covered with red, tuft-like worms. In 2004, Rouse, Goffredi, Vrijenhoek and colleagues reported them as the new genus Osedax in Science (vol. 305, pp. 668–671). The name means "bone-eater" in Latin.

No mouth, no gut: how do they eat bone?

Osedax are polychaete worms. According to JAMSTEC, they have no mouth, anus or gut, and take in nutrients by sending "roots" into whale bone. Symbiotic bacteria in the roots are thought to help break down lipids and collagen in the bone. The red tufts act as gills that take in oxygen from the water.

A bone-eating history reaching back to the Cretaceous

The team suggested that Osedax's bone-eating lifestyle began in the Cretaceous (about 145 to 66 million years ago), before marine mammals appeared. European researchers later reported traces thought to be made by Osedax in the bones of plesiosaurs and sea turtles, supporting the idea. Bone-eating worms may have lived on the remains of marine reptiles long before whales.

Relatives of Osedax have also been found in Japanese waters; a species named Osedax japonicus is known. In Japan too, whale carcasses quietly sustain life.

Whale-fall research in Japan: off Cape Noma and Sagami Bay

The sinking experiment off Cape Noma

Off Cape Noma on the Satsuma Peninsula in Kagoshima (about 200 m deep), an experiment was carried out in which the carcass of a stranded sperm whale was placed on the seafloor. According to JAMSTEC cruise reports, surveys were carried out every year for three years from 2003, tracking changes in the community around the bones.

The survey found new species such as bone-eating worms and a lancelet associated with whale bones. A community centered on two mussel-family species hosting chemosynthetic bacteria (Adipicola pacifica and a relative) was also confirmed. The 2005 report notes that the community was changing as the bones weathered, and the 2006 report suggests chemosynthetic communities persisted after soft tissue had almost disappeared.

Why has research advanced in Japan?

Japanese waters have relatively frequent whale strandings and topography that gives easy access to the deep. JAMSTEC's submersibles and robots allow regular surveys of seafloor at hundreds to thousands of meters. The 2008 cruise report set out a policy of continuing experimental surveys in different sea areas and depths to clarify the role of whale bones.

• Sinking experiments let us follow succession over time
• New species discoveries deepen understanding of biodiversity in Japanese waters
• Continued observation shows how communities change as carcasses shrink

Figures and years in cruise reports may be written differently from report to report. Please check the originals published by JAMSTEC/GODAC.

Carbon carried by whale bones: a deep-sea carbon store

Where does a sunken whale's carbon go?

Nearly half of a whale's body weight is organic matter containing carbon. When the carcass sinks, this carbon is cut off from the surface and stays near the seafloor for a long time. Within the ocean's carbon uptake, whale falls are thought to be a small but distinct "carbon pathway".

A 2010 study by Pershing et al. (PLoS ONE) estimated that the decline of large baleen whales through whaling reduced carbon stored in the ocean by about 9.16×10⁶ tons. It also estimated that if whale populations recover, sinking carcasses could carry about 1.66×10⁵ tons of carbon per year to the deep sea. The estimate depends on assumptions such as the fraction of carcasses that actually sink; the study assumed about 50% of rorquals and gray whales and about 10% of right and bowhead whales sink to depth.

Do not over-sell it as a "climate silver bullet"

Carbon transport by whales is small relative to the whole ocean carbon cycle. Commentary on the research also stresses that it is comparable in size to other carbon-management schemes but highly uncertain. Protecting whales matters not only for climate but also for protecting whole ecosystems. When converting numbers into "tons of CO₂ per whale", check the assumptions.

The history of whaling and whale falls: how many "oases" were lost

What happens when carcasses become fewer?

Large whales were greatly reduced by past whaling. Fewer whales mean fewer carcasses reaching the deep sea. Animals that depend on whale falls survive when larvae swim from one carcass to the next oasis. Fewer carcasses widen the gaps and may lower the chance that larvae arrive.

How much whaling affected specialists such as Osedax is still not well understood. Still, large carcasses are clearly a valuable food source, and conservation discussions now pay attention to the roles whales play "after death" as well as alive.

Links between coast and open sea

While alive, whales bring surface nutrients to the sea through their waste, helping phytoplankton grow. After death, they deliver nutrients to the deep over a long time. Having these two faces, alive and dead, shows how heavily whales weigh in the ecosystem.

Why study whale falls: how do we protect the deep sea?

Relation to deep-sea development and fishing

Interest in deep-sea mineral development and deep-sea fishing has grown. Deep-sea biodiversity is still barely surveyed and slow to recover once damaged. Ecosystems that form over decades, like whale falls, call for particular care in impact assessments.

What citizens can do

• Report stranded whales to local aquariums or research institutions (do not touch or take anything away)
• Learn where to send information on whale strandings and drift ashore
• Join exhibitions and events about whale bones to broaden interest in the deep sea

The deep sea may feel far away, yet what happens there is tied to the health of our seas and the climate. Learning about the deep sea through something as familiar as a whale carcass is a first step to protecting the ocean.

Summary: even in death, whales support the ocean

A sunken large whale brings 30–160 t of organic matter to the deep and feeds many animals: hagfish, sharks, polychaetes, bone-eating Osedax and sulfur-powered bacteria. Chemosynthesis using hydrogen sulfide shares its form of sun-independent life with hydrothermal vents and cold seeps.

Off Cape Noma in Japan, sinking experiments with stranded whales produced new species and long-term observations of succession. Research is also advancing on how whaling-driven declines have affected ocean carbon storage and deep-sea ecosystems. Though the numbers are uncertain, understanding that whales contribute to the sea both alive and dead will be a foundation for future ocean conservation.