In Homer’s epic poem, the Iliad, we are introduced to the κητος (pronounced care-tos) a most ghastly and terrifying serpent dwelling in the depths of the Mediterranean Sea. When Queen Cassiopeia of Ethiopia claimed that her daughter Andromeda was fairer and more beautiful than the Neirids, nymphs that often accompanied Poseidon, the God of the Sea was so enraged that he sent the κητος to destroy the Ethiopians. Cassiopeia and the King consulted a wise oracle, whose advice was to sacrifice Andromeda to the great beast. And so Andromeda was lashed to a rocky outcropping, abandoned to the mercy of the terrible beast. Just as the κητος prepared to devour Andromeda, she was saved by Perseus, who used Medusa’s head to end the beast’s tyranny once and for all. That beast’s classical name, latinised as ‘cetus’, is the basis for the modern te
rm ‘Cetacea’, which is used to describe a large group of aquatic animals including whales, dolphins and porpoises.
The death of κητος described by Homer – petrification, a sudden transformation into cold, ossified stone – reflects greatly our perception of our own deaths. We so often liken our deaths to the extinguishing of a flame. Our skin, marked by experience, cracks and grimaces. Our unique and powerful brains slow and meander. Humans die in monochrome. Cold and rigid, the End creeps into the periphery of our vitality, lapidifying us until the final flicker of warmth has faded away. However the death Homer describes couldn’t be further from the actual processes that would have taken place at the natural end of κητος ’ life. Whales do not grow cold. They get hotter, boiling inside their coat of blubber. The same processes and pressures that generate this immense heat are responsible for blooms of appalling colour that begin to adorn the carcass: pinks and reds emerge from the bloated specimen as immense pressures building from deep within the animal push organs, blood vessels and fluids to the surface. Every now and again – though with increasing regularity as whales become the landfills of our putrefying oceans – we become witnesses to this gruesome spectacle as these behemoths become irreversibly beached.
We are so fascinated by whales largely because they seem so alien. Incomprehensibly vast, they live long, mysterious lives in our deepest oceans – habitats that lack anything that we consider necessary for life. The deep ocean is indeed an unforgiving place. Darker than any night experienced on the surface, as quiet as the depths of space and dishing out pressures one hundred times those on land. For nearly all of human history, we have considered life at these depths to be an impossibility. However, work in the last few decades has revealed a startlingly diverse group of organisms thriving in the depths. One of the major bodies of work that yielded such discoveries was carried out by oceanographer Craig Smith off the coast of California in 1987. Smith and his group had set out to map the ocean floor at depths of around 1 km with their trusted Alvin submersible, when the tiny vessel identified something massive in the darkness below. As group descended lower, Smith and his team were astonished to find an almost entirely intact skeleton of a blue whale, slowly decomposing on an outcropping on which it had settled. However, this was no ordinary collection of bones. Smith and his team observed a teaming, diverse collection of organisms thriving in amongst the decomposing tissue. Smith’s team – and countless others in the years since – observed a myriad of crustaceans and thread-like worms crawling over the remains of the creature – grass on its grave. So to did industrial fishing vessels as they hauled aboard bones and skulls tempestuous with life.
So-called ‘Whale Falls’ have since been found to a crucial source of biodiversity, harbouring as many as 30 species found only in these niches. As the species feasting in the depths were characterised in greater detail, Smith and his team discovered the presence of a range of chemosynthetic organisms – organisms that derive their energy through the metabolism of a range of organic molecules – that have been previously shown to underpin entire ecosystems. Smith suggested that with an estimated 690,000 whale carcasses decorating the sea floor, as close to 12 km away from each other along feeding routes, these chemosynthetic organisms could maintain so-called “hotspots” of life, close together enough for larvae, bristle worms and other small organisms to drift between them.
In the years since Smith’s discovery, three distinct phases of the prolific afterlife of whales have been identified (see Figure 1). Most whales that die a natural death are in poor nutritional health. This, coupled with the fact that there is no longer a large volume of air filling their lungs, makes whale carcasses negatively buoyant. As they begin their descent, larger fish strip away the soft tissue and underlying organs in a process that can take up to two years.
As the carcass settles, a large but relatively poorly diverse pool of opportunists scavenge the remaining tissues spreading through the sediment and feed on the newly exposed bones. The skeleton takes on a new form, a canvas of marine hieroglyphs dotted with bristle worms and crustaceans.
Finally, after another two years, even smaller organisms arrive to break down the invisible morsels – fine dining on a molecular scale. Organisms housing specialised bacteria arrive to break down lipids contained deep in the bones. With little oxygen dissolved in the water at these depths – most atmospheric oxygen has been used up by bacteria at shallower depths – anaerobic bacteria break down the lipids in the heart of the bones. This process releases hydrogen sulphide gas, a highly toxic substance. However, exemplifying the nature of the highly interconnected ecosystems that centre on whalefalls, sulfophilic bacteria – which are able to chemosynthetically derive energy from sulphur-containing molecules – rapidly oxidise this hydrogen sulphide into energy that can be transferred to other nearby organisms, either through symbiotic relationships or through direct feeding. Termed the sulfophilic stage, this continuous lipid digestion and energy production is thought to last up to one hundred years and be the major energy source that perpetuates the burgeoning ecosystem.
Groups in both Japan and Sweden have reported the same findings as Smith, adding fuel to the theory that whale falls provide stepping stones for sulfophilic bacteria and the organisms that interact with them to spread along the ocean, from niche to niche. There are, however, some who believe that the story is more complicated than that. Smith’s version of events relies on there being little dissolved oxygen at the point at which the whale carcass settles. With greater oxygen concentrations come a wider variety of aerobic bacteria that would speed decomposition and hence allow less time for an ecosystem to establish itself.
Additionally, the prevalence of certain organisms could speed up the decomposition in whalefall communities.
Recent studies have discovered the presence of a genus of worm called Osedax (see Figure 2) derived from the latin meaning ‘bone-eating’, at whalefall sites. These curious organisms, whose alien features range from devouring on decomposing bones to all adults being female, with all males never reaching adulthood and whose only function is to produce sperm, can rapidly increase the timeline of the sulfophilic stage as they compete with the sulfophilic bacteria for the breakdown of bone lipids. If, as is now being considered, Osedax are a major presence in the decomposition of whales, the stepping stone theory – which relies on whalefall communities developing on a consistent and long-term basis – may be under threat.
Regardless of just how whalefall communities interact with each other, it is clear that the prolific afterlife of whales provides the stage for a century-long bloom of biodiversity, transforming the cold, dark waters of the deep oceans into a thriving thoroughfare. With as many as thirty species found only in whalefall communities, it would appear that whales – far from the terrible κητος – are just as valuable to the deep oceans in death as they are in life.
‘Til next time…