A survey of animals that live on the sea floor suggests that they are less likely to be bioluminescent than are species that swim freely at similar depths.
Sönke Johnsen at Duke University in Durham, North Carolina, and his colleagues dredged species (examples pictured) from 500–1,000 metres below the sea surface around the Bahamas, and examined them in tanks. Fewer than 20% of the creatures glowed, whereas roughly 80% of free-swimming species from similar depths are bioluminescent.
In a separate study, Johnsen, along with Tamara Frank of Nova Southeastern University in Dania Beach, Florida, and another colleague eased eight species of floor-dwelling crustacean up from the sea floor 500–700 metres down around the Bahamas and in the Gulf of Mexico.
The researchers kept the animals in light-tight boxes to protect their sensitive photoreceptors, and found that the creatures could best detect blue light — that is, wavelengths similar to those that filter through the water from the surface and are emitted by bioluminescent species. Some of the crustaceans had eyes that were sensitive to dim light, but were much less responsive to movement.
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Glowing is rare on the sea floor. Nature 489, 338 (2012). https://doi.org/10.1038/489338a
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DOI: https://doi.org/10.1038/489338a
