Researchers from the Queensland Brain Institute at The University of Queensland have uncovered a new form of secret light communication used by marine¹ animals. The findings may have applications in satellite remote sensing, biomedical imaging, cancer detection, and computer data storage.

 

Dr Yakir Gagnon, Professor Justin Marshall and colleagues previously² showed that mantis³ shrimp⁴ (Gonodactylaceus falcatus) can reflect and detect circular polarising light, an ability extremely rare in nature. Until now, no-one has known what they use it for. 

 

The new study shows the shrimp use circular polarisation as a means to covertly⁵ advertise their presence to aggressive competitors. 

 

"In birds, colour is what we're familiar with; in the ocean, reef fish display with colour. This is a form of communication we understand. What we're now discovering is there's a completely new language of communication," said Professor Marshall.

 

Linear polarised light is seen only in one plane, whereas circular polarised light travels in a spiral - clockwise or anti-clockwise - direction. 

 

The team determined⁶ that mantis shrimp display circular polarised patterns on the body, particularly on the legs, head and heavily armoured tail; these are the regions most visible when when they curl up during conflict.

 

"These shrimp live in holes in the reef," said Professor Marshall. "They like to hide away; they're secretive and don't like to be in the open."

 

Researchers dropped a mantis shrimp into a tank with two burrows⁸ to hide in: one reflecting unpolarised light and the other, circular polarised light. The shrimp chose the unpolarised burrow⁷ 68% of the time - suggesting the circular polarised burrow was perceived as being occupied by another mantis shrimp.

 

"If you essentially⁹ label holes with circular polarising light, by shining circular polarising light out of them, shrimps¹⁰ won't go near it," said Professor Marshall. "They know - or they think they know - there's another shrimp there.

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