Bioluminescence: Lighting up a lightless world. 

While bioluminescence is everywhere throughout our Ocean, it’s the only source of light in the deep-sea. 

A staggering 76% of all Oceanic marine animals are capable of bioluminescence, which means that they can produce their own light through chemical reactions inside their body.  

How does bioluminescence work in the deep Ocean?  

Bioluminescence is a chemical reaction that occurs when the light-emitting molecule called luciferin reacts with a luciferase enzyme, releasing energy in the form of light. 

It’s an active process, meaning it can be turned on/off, as opposed to the passive traits of fluorescence and phosphorescence. 

Some bioluminescent organisms generate their own light. Others take up bioluminescent bacteria from the water column and house it in their light organs in a symbiotic relationship. 

Marine bioluminescence is commonly expressed as blue/green light. This is most likely because these wavelengths travel further distances through the water. They’re more also easily visible in the deep Ocean.   

In rarer cases, red and yellow bioluminescence have also been observed in marine creatures.  

Why do marine animals emit light at all?   

In the lightless world of the deep Ocean, marine creatures have adapted to use bioluminescence to their advantage:  

1. Deep-sea anglerfish have a specialised lure to attract prey. 

Perhaps the most famous bioluminescent predator is the deep-sea anglerfish.

This ferocious hunter has a large head, incredibly sharp teeth and a long, fishing-rod-like structure that extends out from the top of its head. At the end of this rod is a ball (called the esca) which contains glowing bacteria called Photobacterium. Ringing any bells? You may recognise her from Finding Nemo.

This lure is used to attract curious prey and is also useful for finding a mate in the vast, dark expanse of the deep Ocean. 

2. Vampire squid expel bioluminescent mucus to deter predators. 

When threatened, the vampire squid inverts its body, raising its arms over its head to expose rows of spikes to deter attackers.

And if that’s not deterrent enough, they also eject a sticky, bioluminescent mucus which can startle, disorient, and confuse predators.

This defensive tactic can buy the squid enough time to escape, while also covering its predator in brightly lit fluid, leaving them vulnerable to attack.  

3. Stoplight loosejaw dragonfish have red flashlights to see in the dark. 

Stoplight loosejaw dragonfish have special red-emitting light organs beneath their eyes that can be activated to look for prey.

The stoplight loosejaw is the only known animal to use chlorophyll pigments (usually found in plants) inside its eyes, which allows it to see red wavelengths of light. 

They use these red beams as a flashlight to search for prey. Since most deep-sea fish can only see blue light, these predators have a huge advantage. They can see their prey, but their prey can’t see them.

4. Lanternfish use light to blend in. 

Lanternfish have adapted an ingenious ability to camouflage themselves using light. 

These masters of disguise have rows of photophores (light-emitting organs) on their underside. They emit a faint glow which allows them to blend in with any remaining light that filters down from the surface.

This process is known as counter-illumination and renders them almost invisible to attackers hunting from below.  

Some marine animals use counter measures against bioluminescence in the deep Ocean.   

Light from bioluminescence has the potential to reveal the whereabouts of creatures that hide in the darkness of the deep Ocean. 

To counter this, many take measures to disguise themselves or break up their outline. 

Many deep-sea creatures are dark red in colour. Red wavelengths of light are the first to be absorbed in the Ocean, and very few deep-sea creatures can see red light (the stoplight loosejaw being a notable exception). Red-coloured creatures therefore appear black and blend in against the near-lightless backdrop.  

Others have ultra-black skin that can absorb light from bioluminescence. For example, pelican eels are found in the midnight zone (where there’s no sunlight, and life exists in complete, constant darkness). Their skin can absorb up to 99.7% of light, rendering them virtually undetectable, even when exposed to bioluminescence. 

Transparency is another technique used for camouflage in the deep Ocean. The glass squid has been observed as deep as 2,000m, and is almost completely transparent. The only organ visible through the tissue of this small-tentacled, swollen-bodied squid is the red-coloured digestive gland. This makes it difficult to be spotted by even the most astute predator. 

Human ingenuity often takes inspiration from nature, and bioluminescence is no exception. 

Due to its unique ability to produce light without the need for an external light source, bioluminescence has been utilised in the field of medical research.

Particularly in imaging and probe techniques for cancer detection and cell culture research, bioluminescence has helped us to detect and respond to disease more effectively.  

With so much of the deep Ocean left to discover, each unique finding may lead to new and exciting medical applications.  

Bioluminescence, therefore, not only lights up the lightless world of the deep Ocean but can also shine a light on our human mysteries too.  

Post by

Jemma Sargeant

A dead whale descends into the darkness of the deep-sea abyss.

In life, these majestic creatures travel vast distances playing an important role in surface ecology. But even in death, their decaying remains become a haven of life on the black Ocean floor.

Here in the deep Ocean the environment is sparse, offering fewer resources to sustain life. What falls from above, marine snow, is the steady trickle of dead organic material and supports an array of life on the seabed. 

A dead whale is a 30-tonne avalanche of fat and organic carbon, equivalent to more than 1000 years’ worth of marine snow across 100 square meters. 

Eventually, a whale fall (a whale’s death) becomes an island of biodiversity in the deep-Ocean.

1. It all starts with a feeding frenzy. 

Soon after the whale falls, a variety of species descend upon it and the dinner party begins.

The first to arrive are the large Ocean wanderers such as hagfish (eel-shaped jawless fish) or gigantic sleeper sharks. These mobile scavengers remove soft tissue by rasping or tearing at the flesh exposing the energy-rich skeleton, giving the name of this phase the mobile-scavenger stage.

2. As the pieces get smaller so do the scavengers. 

It can take up to two years for the mobile-scavengers to finish feeding on the whale, where the next wave of guests arrives in a second phase known as the enrichment-opportunist stage.

Animals like polychaetes (a class of marine worms) and crustaceans including amphipods (shrimp-like crustacea) will move in to feed on remaining blubber and burrow into the nutrient enriched sediments surrounding the whale.  

3. Finally, only the bones of the whale remain.

These would seemingly have no further use. However, ecological diversity is about to flourish in the sulfophilic stage of the whale fall. The whale’s bones provide a large reservoir of energy-rich lipids, a shining prize to deep-sea organisms. 

Bacteria break down fatty lipids in the bones, releasing sulphides. The sulphides can be used to generate energy, in a process called chemosynthesis (producing food using chemicals as an energy source instead of sunlight).

These chemosynthetic bacteria have become resistant to sulphides’ toxicity and can establish bacterial mats which act as a foundational food source, supporting a huge array of marine biodiversity: sponges, mussels, limpets, sea spiders and snails.

The breakdown of bone-lipids can take 50-100 years and these mini-ecosystems are highly significant for seabed ecology. Even then, after the complete extraction of nutrients, it isn’t over.  

Decades after a whale dies, the whale-fall is still essential to marine ecosystems:  

Some scientists believe there’s a further stage of succession: the reef stage. Even after the feeding frenzy, the whales’ bones can remain for more than 100 years, acting as hard surface for suspension feeders to settle.

These ‘habitat islands’ act as evolutionary stepping stones between other seafloor ecosystems like hydrothermal vents. This may have allowed sulphide-specialised organisms to spread across the seafloor and diverge into new species. 

Despite whale-fall ecosystems being poorly sampled, 407 species have been found living off the carcasses globally, which is high for the bottom of the sea. Of these, 21 species can only be found on whale-fall, known as whale-fall specialists.

Whale-fall specialists are species that require a whale carcass to complete their lifecycle and maintain their populations. These marine organisms will jump from habitat island to island to survive.

For example, Osedax, Latin for “bone-eater”, are a genus of polychaetes (marine worms) found worldwide.  They are important ecosystem engineers by eroding whale bones and allowing rarer species to colonise the whale skeleton.  

How whale populations impact the global Ocean? 

Whale-falls also contribute to the conversion of inorganic carbon (CO2) into organic carbon (marine life), a set of processes known as the Biological Carbon Pump (BCP). This carbon is sequestered (stored) in the deep Ocean.  

Whales deliver huge amounts of carbon in their biomass to the seafloor, which is then locked-away for centuries within deep-sea sediments.

Any threat to whale populations will threaten entire ecosystems and disrupt the process of carbon sequestration.

Commercial whaling, for example, has been depleting whale populations for around 1000 years, beginning in 1000CE. Experts agree that tens of millions of whales were likely killed during this period, pushing many whale species to extinction and causing the extinction of whale-fall specialist species, who rely on whale falls for survival.

A single whale-fall can provide everything a whale-fall specialist needs for 50-100 years, meaning there is a lag-time of at least 30-40 years before the decline in whale populations is felt. Which is to say, if whale populations can recover, we may be able to mitigate the impacts on deep-sea ecosystems

As we follow the timeline of a whale’s life, we can see the incredible contribution whales make to the Ocean.

From enhancing surface ecology in life, to supporting entire ecosystems in death. 

Post by

Olivia Jones