Luminous Squids and Ultra-Black Pacific Blackdragons: Shades of Life, Light, and Survival

1,107 total words    

4 minutes of reading

Photo Credit: Bobtail Squid, by NOAA

The photons appear to be frolicking in the ocean’s soft curls, inchoate at first and then congealing across the water’s broad expanse. The photons lie in a gentle embrace, slowly spreading their limbs out, as if caressing the curls. The ocean’s ripples make little sulci and gyri there, then disappear—just as life and consciousness does, projecting the vitality of myriad and vibrant life forms beneath. Silvery birds of the sea glide through the water, some in shoals, as little crabs make themselves comfortable on the rocky edges, the ocean lapping at them gently—a puppy demanding a walk, prodding the crabs that sat, nonchalant. Some silver finds itself spooned into the orange of a seagull’s beak, becoming a part of her being, allowing her to survive another day. 

Light has been life’s ally, molding and coaxing creation; working—infinitesimally—in tandem with evolutionary processes. Or perhaps life has flourished using the melange of tools at its disposal, light being one such key tool. Maybe both scenarios are at play—light as progenitor and as implement? Light and its antithesis have slotted themselves into the rhythms of life, accounting for the “coos” of some birds at dawn and the crepuscular wanderings of owls and rodents at night. Chronobiology, photochemistry, evolution, physics, mate selection in birds, art and aesthetics are all holding hands. 

As our deep-sea camera slowly inches its way into the burgeoning bosom of the water’s depths, two fascinating life forms catch our eye, bursting forth, with millions of others, from the very bosom that nurtures and sustains them. The Hawaiian bobtail squid (Euprymna scolopes) and the ultra-black Pacific blackdragon (Idiacanthus antrostomus) exist as light-emitting and light-absorbing yin and yang, respectively. The squid owes part of her survival, as well as her very being, to the crucial tenant that is ensconced in the bilobed light organ of her mantle cavity. These cohabitants are the bioluminescent bacteria called Vibrio fischeri. In a process entailing a mutual barter system of sorts (mutualism), the bacteria happily partake of much-needed essential nutrients that the squid has to offer while assisting her in her survival through the process of  “counterillumination.”

The term—scientific though it is—does little to convey the awe-inspiring and surreal nature of this illumination process. Perhaps language itself fails. The process is far richer when captured in one’s imagination, where the words do not form barriers and the images birthed have free reign to flow. Language can describe, delineate, poeticise, paint, philosophize, but without its twin, imagination, it is hollow. One can thus imagine, once the V. fischeri begin to bioluminesce by the light of the moon within the mantle cavity of  the nocturnal Hawaiin bobtail, that a bluish glow is tuned such that it matches that of the downwelling moonlight. 

Bioluminescence occurs as a result of several carefully controlled chemical reactions, genetically mediated, in which the bacterial luciferase is a key player. It is thus a kind of chemiluminescence that involves an enzyme, emitting light as a result. As opposed to appearing conspicuous, the squid in fact blends in, lessening any silhouettes that would have been present were it unable to counter illuminate itself. By doing so the squid is more likely to be hidden away from her prey and possibly to better avoid any dangerous predators. Such is her iridescent survival strategy—or, rather, such is nature’s unique way of equipping these squids with survival mechanisms that guide them in a life of coruscating magnificence, a symbiotic partnership that glows.

As the Hawaiian bobtail squid and V. fischeri go through their life cycle in the shallow waters, emitting light for survival, our deep-sea camera now finds itself in a different location. As it plunges into the water’s depths, an inky blackness starts to envelop it. Idiacanthus (also known as the black-dragon), like a few other ultra-black deep-sea fish, are in some ways a complete antipode to the pole of bioluminescent squid—though both are trying to blend in, just in different ways. They represent the organic embodiment of the darkness, the true nature of reality. What concreteness does light have without life and consciousness? Stripped of its luminosity, the black dragon would be one with the darkness, its absolute truest self. The darkness spills into the infinite; it is beautiful, just as its complementary self (light) is—perhaps more so. Picturing darkness as a mere absence of light diminishes its essence. We are well aware that visible light is only part of the spectrum. Thus, the perception of darkness itself is relative, for when it seems dark for humans (at least, in our technologically non-assisted states), it may not be so for some other species (such as those that can perceive infra-red wavelengths). 

The blackdragon possesses a type of ultra-black skin due to the presence of melanosomes. These are a densely packed, continuous layer, with nary an unpigmented gap, that allows for most of the light from bioluminescent sources to be absorbed. This means that the light blackdragons reflect is very minimal, allowing these sea creatures to meander through the ocean virtually undetected, almost one with the jet-black water at these depths. What distinguishes these fish from the water surrounding them are the patches of aliveness that they encapsulate. The geometry of melanosome arrangement is an important factor as well, in terms of its ability to conceal itself from the searchlights of predators and the defensive mechanisms employed by prey. The slightest misalignments or differences in structure of the melanosomes, and these deep-sea fish may not have had the ability they do. This survival strategy to reduce reflectance, where most of the light is absorbed by the melanin pigment in its melanosomes, is quite unusual when compared to other ectothermic vertebrates. The survival strategies described above may appear foolproof, with no chinks in the armor. However, this is not the case. They are just that—merely strategies that have unfolded over millennia to offer an advantage. Every life form out there has one: some sort of built in mechanism to increase the odds of surviving and perpetuating its kind.

The squid is lighting up; the blackdragon is melding into the abyssal water. Both are trying to exist. One can only wish them well in their fight for survival, until they eventually perish, making room for more squids, blackdragons, and millions of other creatures.


B. W. Jones and M. K. Nishiguchi, “Counterillumination in the Hawaiian Bobtail Squid, Euprymna scolopes Berry (Mollusca: Cephalopoda),” Marine Biology 144, no. 6 (2004): 1151-55.

A. L. Davis et al., “Ultra-Black Camouflage in Deep-Sea Fishes,” Current Biology 30, no. 17 (2020): 3470-76.

J. W. Hastings and K. H. Nealson, “Bacterial Bioluminescence,” Annual Review of Microbiology 31, no 1 (1977): 549-95.

  • Anushikha Bhas

    Anushikha Bhas holds a Master’s Degree in Sport, Health and Exercise Science from the University of Exeter, UK and a Bachelor’s Degree in Microbiology, Zoology, and Chemistry. She has multi domain experience in the field of life sciences, sport and health. Her interests span across domains of sport, art, science, literature, and creative writing.

More Stories & Ideas

Scroll to Top