What is whale fall?

Deep Dives V

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Welcome to another edition of Deep Dives by Beached - an in-depth exploration of everything oceanic, from scientific discoveries to marine mysteries.

Expect a bit of history, science and adventure, as we dive deep into the big blue 🤿

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Photo by Brooke Pyke.

Whales are the makers of a healthy ocean. Their poo fertilises the carbon-offsetting phytoplankton, key to fighting climate change. They spread essential nutrients on their migratory journeys around the world, feeding microorganisms and sustaining marine ecosystems as they go. These perfect custodians of our planet are fundamental to the ocean even in death. For when a whale’s life ends, another story is just beginning. 

Referred to as ‘whale fall’, when a whale dies and its body falls to the ocean floor, it provides a wealth of sustenance to deep sea inhabitants. A ‘true whale fall’ occurs when the carcass sinks to the bathyal or abyssal zone, finally coming to rest on the ocean floor. Bathyal, also known as the midnight zone, is somewhere between 1000 to 4000 metres deep, and the abyssal zones, where life is lived in perpetual darkness, is anywhere between 4000 to 6000 metres below the ocean surface. 

The conditions of these deepwater regions are ideal for slow decomposition as fewer large scavengers live this far down. In coastal oceans, the high rate of predators in the shallow, warmer waters quickens the decomposition process, and if decompositional gases are keeping the carcass afloat then those higher up in the water column will have their feast before those on the ocean floor even know about it. They are instead left with the scraps of the skeleton, which are still nutritious for some organisms, but a fully formed ecosystem has lost the opportunity to flourish. 

Fortunately, the cold temperatures of the deep sea significantly slow the rate of decomposition and high hydrostatic pressure increases gas solubility. Based on these perfect conditions, it’s no surprise that scientists have estimated a whopping 690,000 carcasses or skeletons of the nine largest whale species are in one of the four stages of decomposition at any one time.

Photo by Craig Smith - NOAA.

The four stages of whale fall decomposition 

Stage 1

Speedy scavengers are first in line at the buffet, consuming the soft tissue including the much sought after fat stores. Hagfish and sleeper sharks are among those who build the foundations of a blossoming blue ecosystem and though they’re quick off the mark, this stage can last for as long as 18 months. 

Stage 2 

Dubbed the “enrichment opportunists’”, those introduced in Act II Scene I prefer to seize the bones and the surrounding nutrient-rich sediment or any other remaining detritus that’s up for grabs. Worms, crustaceans, mollusks and other critters will gorge themselves for around five years in this second stage of decomposition.

Stage 3

Whale bones are rich in lipids so when bacteria breaks down these fatty parts it nourishes deep sea shellfish like mussels, clams, limpets and sea snails. The lipids make up 4-6% of the whales body weight which means this stage can last for up to 100 years. The term ‘all you can eat’ was coined here in stage 3. 

Stage 4

The final stage is known as the ‘reef stage’. When only minerals from the bones are left and all other organic matter is gone, filter feeders will rest on these solid surfaces. This final process can last for decades or until there is no more space for any more animals, whichever comes first. 

Photo by OET/NOAA.

How this benefits the ocean

A whale’s carcass is a concentrated food source that can support a rich community of over 200 species for more than a century. It also provides evolutionary stepping stones for multiple lineages to move and adapt to growing threats such as climate change. It’s important that those in the deep ocean learn to adapt to the coming onslaught of the effects from the climate crisis, effects that will be evident to them in the bodies of fallen whales.  

How this benefits us 

The depletion of large whales (and therefore a reduction in whale falls) by the whaling industry is believed to have cost the deep ocean a total biomass loss of 30%. This means the massive amounts of carbon that would have otherwise been stored in the deep ocean in the event of a whale fall, is also lost. 

Whales help to sequester carbon throughout their lives, but in a single whale fall around two tonnes of carbon (in relation to a 40-tonne carcass) can be locked away for hundreds or thousands of years. By other means, this would take almost 200 years for the same amount of carbon to reach the abyssal zone, and it would take thousands of trees to reach an equivalent in carbon sequestering. In just one Californian marine sanctuary, whale fall accounts for 60% of their annual carbon sequestration.

This is the benefit of whale fall. 

As I write Beached each week, I often wonder if there is anything that whales do which doesn’t benefit us or the oceans they live in. Their daily habits of pooing at the surface, travelling vast distances with key nutrients on their back, and even encouraging their curious calves to say hello to a whale-watching tour: are all a blessing. 

Just by existing whales keep our planet healthy. Save the whales. Save the world.

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Amie 🐋