On ocean floor, a shrimp that vomits light

The submersible had an arm that allowed researchers to poke creatures to determine if they glowed. Only one out of every five bottom-dwellers cast a glow, a relatively low number, the researchers said.

In 2011, researchers with the University of Aberdeen’s Oceanlab used a remote ultra-sensitive camera to capture bioluminescence at the Atlantic Ocean floor at depths two to three times that of the Caribbean research. The U.K. researchers found relatively high levels of bioluminescence on the ocean floor, much of which came from organisms bumping into rocky terrain.

Color vision?

At half a mile below sea level, the water above filters out most of the sunlight spectrum and leaves only blues. Because of this, researchers figured that ocean bottom creatures would be colorblind — after all, most of them are foraging in nearly complete darkness. [Vision Quiz: What Can Animals See?]

To their surprise, the researchers found some sea creatures such as crabs could detect blue light along with ultraviolet and violet light.

"There is absolutely no UV and violet light coming down at that depth, it's long gone," Johnsen said. So why do the creatures use their resources to detect UV and violets?

The duo-color detection could help animals distinguish between the bluish edible plankton and the greenish potentially poisonous animals that live at the ocean bottom, researchers hypothesized.

"It is only a hypothesis, we could be wrong," Johnsen said. "But we can't think of another reason why an animal would use this ability to see UV and violet light because there isn't solar light left."

In the future, the researchers hope to verify their color-coding hypothesis with behavioral experiments of the deep-sea creatures in a lab setting and eventually to return to the deep sea to find more benthic animals that detect UV and violet light.

The Journal of Experimental Biology published the results in two separate papers today (Sept. 7).

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