Light in the Deepest Depths, Part 2

Welcome to the deep sea. No sunlight penetrates this far down; pitch blackness, no sense of direction. Out of nowhere, a dim flicker of light…

In Part 1 of this two-part series, we looked at how these denizens of the deep survive their virtually inhospitable habitats under 1,000 times standard atmospheric pressure. In this installment we will look at another marvelous adaptation of these creatures: generating light.


Hello world. (Flickr)

Bioluminescence is the ability of a living organism to produce its own light. Amazing in itself. But when we contemplate that it is simply energy released from a chemical reaction, sort of like a light bulb, the simple complexity breathtaking.

Well, it is completely unfair to compare bioluminescence with light emitted from a bulb. That would be sort of like comparing a maglev to a steam engine.


Okay, so the steam engine looks wicked.

In a light bulb, ~90% of energy is converted to heat, giving it a measly 10% efficiency, emitted as direct light. In bioluminescence, the efficiency of light production is much higher at ~41%1 – such that the organism expends only a small amount of energy sustaining this ‘cold light’.

The molecules responsible for all bioluminescence are known as luciferins, which release light via a catalyzed oxidation/excitation followed by an electron transfer reaction as the molecule returns to the ground state. These luciferins – as well as their catalyst partner luciferases – differ from species to species, and most have yet to be studied in detail.

(For those interested in the electron transfer mechanism for firefly luciferin)

Deep sea creatures are known to possess the luciferin known as vargulin, but they catalyze their vargulin using a different array of luciferases. These catalysts are therefore what lend deep sea creatures their myriad of exciting colours.


What, then do they use all this light that they produce for? I mean, they don’t have good eyesight to begin with. So why the fuss? Because many reasons, that’s why. Shown below is a list (not exhaustive, of course) as to what these creatures can do with a little light.


Extremely cute infographic, complete with confused-looking fish2


  1. Yue, L., Lan, Z., & Liu, Y. J. (2015). The theoretical estimation of the bioluminescent efficiency of the firefly via a nonadiabatic molecular dynamics simulation. The journal of physical chemistry letters, 6(3), 540-548.
  2. Haddock, S. H., Moline, M. A., & Case, J. F. (2010). Bioluminescence in the sea. Annual Review of Marine Science, 2, 443-493.

(Post featured image via Flickr)

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