The Stages of Whale-Fall Ecosystems.

For the most part, the nutrients found in the depths are supplied by a steady steam of organic debris falling down from shallower waters. It's not much, but it tends to be enough to sustain the sparse and barren depths. But every now and then, something much larger sinks to the seabed. It draws life from miles around to gather for a feast to last for decades. It is known as a whale-fall.

 

Whale-fall ecosystems support an abundance of life in waves of successive communities. The carrion of the whale is first stripped of all its flesh by larger scavengers, like Greenland sharks. Once all the flesh is gone, and any debris in the sediment has been hoovered up by opportunists like ghost sharks, bacteria break down the bone lipids to produce energy that supports an ecosystem of life around the carcass.

It is thought that whale-falls may have been the crucial stepping stone that allowed deep-sea species to colonise the sea floor.

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Occasionally, a whale carcass will sink to the seabed, and can support a complex biological community for up to 50 years.

Most nutrients in the deep sea are supplied by a steady stream of organic debris, known as marine snow.

Mobile scavenger stage

Lasts 4 months - 2 years

When the carcass comes to rest on the sea floor, the first organisms to arrive at the scene are 'mobile scavengers' - these are the larger ocean wanderers, including hagfishes and gigantic sleeper sharks. Whale-falls attract such an abundance of life because their nutrient content is equivalent to 2,000 years worth of marine snow, providing a rich supply of nutrients concentrated in one small area.

The flesh and soft tissue can support this community of scavengers for up to 2 years. After that time, all that's left are bones, and chunks of organic material buried in the sediment.

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Hagfish

Myxini glutinosa

The hagfish makes use of four pairs of thin sensory tentacles around their mouths in order to seek out the whale carcass. Once there, they use two rows of sharp tooth-like structures to burrow down into the carcass. They are also able to tear off chunks and deliberately tie their long tails into knots. This increases the force of their bites by creating torque.

ENRICHMENT-OPPORTUNIST STAGE

Lasts around 2 years

In this 2nd phase of the whale-fall community, mollusks, worms and crustaceans feed on any blubber that remains. As whale-falls are so rare, nothing goes to waste, so the opportunists will spend 2 years burrowing into the surrounding sediment in search of leftovers.

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Osedax worms

Osedax frankpressi

Commonly called the zombie worm or bone-eating worm, this variety of polychaete worm bores away at the bones of the whale carcass. It does so in order to reach the lipids that are sealed away within the bones. Osedax worms rely on these lipids for nutrients. They were first discovered at a whale-fall site in 2002, inhabiting the bones of a decomposition gray whale on the sea floor nearly 10,000 feet (3,000m) deep.

sulfophilic stage

Lasts 10 - 50 years or more

The final stage can last for decades. Only the bones remain. At first look, you might think it impossible for any substantial community of organisms to thrive from bare bones sitting on the sea floor. However, the ecological diversity of species found during the sulfophilic stage is greater than any other deep sea community.

The sulfophilic stage gets its name from the process of chemosynthesis, during which specialised bacteria break down the lipids present in the bones to produce sulphides. 

The presence of sulphides allows other organisms to thrive here, including dense mats of bacteria, mussels and tube worms. More than 30,000 organisms can sometimes be found on a single skeleton.

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