Strange Deep-Sea Crabs May Color-Code Their Food

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Topics in Chemistry Article #1: Strange Deep-Sea Crabs May Color-Code Their Food

A.    Reading questions (5 points each):

1.      What are three concepts discussed in the article?

2.      Define bioluminescence.

3.      What is the difference between blue and green light (e.g., their energy and wavelength)?

4.      What would happen if crabs ate the green anemones?

B.     Pose one question to post in the discussion about the article (20 points).

C.    Cite literature read in addition to the article presented (20 points).

D.    Discussion questions (5 points each):

1.      How does bioluminescence apply to this case?

2.      Explain why the crabs can sense the difference in blue and green light.

3.      Why is it important for crabs to sense the difference between blue and green?

4.      What happens if they cannot sense the difference between blue and green?

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 Strange Deep-Sea Crabs May Color-Code Their Food

Stephanie Pappas, LiveScience Senior Writer

Date: 06 September 2012 Time: 01:36 PM ET

Gastroptychusspinifer(squat lobster) has a body

that is about 1/2-inch wide and 1-inch long. Its eyes

are quite large for such a small animal.

CREDIT: Image courtesy of Bioluminescence Team 2009, NOAA-OER.

What good is color vision in the dark of the deep sea? For somecrabs, an ability to see blue and ultraviolet light may mean thedifference between chowing down on a good meal versus a toxicone.

A new study published today (Sept. 6) in the Journal of ExperimentalBiology finds that some seafloor, or benthic, crabs can see in color.But the crustaceans live in darkness of the deep Caribbean where

sunlight does not penetrate, making their sensitivity to blue andultraviolet light mysterious.

The reason for the color vision, however, may be explained by theconcurrent discovery of bioluminescent deep-sea plankton in thisenvironment, which glow blue when they bump against objects alongthe seafloor. It's possible that the crabs see this blue glow as a sign ofa hearty meal, said study researcher Tamara Frank, a biologist atNova Southeastern University in Florida.

At the same time, the ability to see blue and UV light would also enable the crabs to tell the difference between bioluminescent blue plankton and the dim greenish glow given off by the anemones where the crabs like to perch. "They just hang out in these plantlike things, and every so often — they have these amazingly long claws — they reach over and they're clearly picking something off and bringing it to their mouths," Frank told LiveScience."It would be really cool if they're picking it off because it glows blue and not green," she added.Frank and her colleagues conducted an exploratory deep-sea mission at three sites near the Bahamas in 2009 on the Johnson-Sea-Link submarine, a Harbor Branch Oceanographic Institute manned submersible. Using the sub's delicate tools, theresearchers are able to gently suction seafloor-dwelling crustaceans into opaque boxes, which are then brought to Frank's lab onthe expedition ship. Lit only by dim red light so as not to upset the dark-oriented crabs' vision, Frank places electrodes on the

crustaceans' eyes to measure their response to different wavelengths and intensities of light. If the eyes respond with anelectrical signal, it means that the crab can detect that type of light.

Frank has found two species, Eumunidapictaand Gastroptychusspinifer, with the ability to see UV and blue light.Meanwhile, on the same voyage, Frank's Duke University colleague SönkeJohnsen was sitting in the submersible, waiting forhis eyes to adjust to the darkness, when he noticed a greenish glow coming from some of the anemones and other plantlikeanimals that live on the seafloor. The plankton bumping into the anemones glowed blue.

Anemones would be toxic to crabs, Johnsen realized, while plankton would make a good meal. That's when he came up withthe idea that perhaps the deep-sea crabs have kept their sensitivity to light in order to differentiate between the bioluminescenceof the two, essentially color-coding "food" versus "toxin."

The idea is only a hypothesis at this stage, and thanks to federal funding cuts to deep-sea research, Frank and her colleaguessaid they may not be able to test it anytime soon, she said.

Bioluminescence is well known in the open ocean, but little is known about the light shows on the seafloor, Frank said: "Thosestudies are just really rare."

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