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How does the bobtail squid use bioluminescent bacteria for camouflage?

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time-lapse photo of fireflies — Bioluminescence Time-lapse image of fireflies in the Catskill Mountains, New York. Firefly light is a cold light, with approximately 100 percent of the energy given off as light and only a minute amount as heat. Only light in the visible spectrum is emitted.

The bobtail squid utilizes bioluminescent bacteria for camouflage through a sophisticated process known as counter-illumination. The squid houses these bacteria within specialized cavities located on the underside of its body.1

When the squid emerges from the sand at night, it adjusts the openings of these cavities in response to the intensity of moonlight penetrating the water above. By modulating the amount of light emitted by the bacteria, the squid effectively matches the downwelling light, which obliterates its silhouette and makes it less visible to predators lurking below.123

The light itself is produced through a specific chemical reaction involving the bacteria. Unlike organisms that produce their own light via the oxidation of luciferin by the enzyme luciferase, these luminescent bacteria employ the enzymatic oxidation of reduced flavin mononucleotide (FMNH $_{2}$ ). In this process, bacterial luciferase catalyzes a reaction between FMNH $_{2}$ and oxygen to form a long-lived intermediate complex, which then reacts with a long-chain aliphatic aldehyde to emit light.45