Mantis shrimp eyes use polarized light to locate objects underwater (2 min read+audio: scientific discovery)

 

Recently, a group of scientists from Australia and the US used a special camera, which mimics the eyes of a mantis shrimp, to show that polarized light can be used underwater to determine the geolocation of an object.

The team took recordings at depths of 2-20 meters underwater at locations all around the world and showed that they could then relocate the camera from the recorded images. They managed to get to within 61 kilometers, or 6 metres of error for every 1 kilometer travelled. This is about the same as the desert ant, which also uses polarized vision.

While this might seem like a large error, marine creatures don’t travel in straight lines or follow fixed compass points. Rather, they make adjustments to their route, changing direction along the way, as you would in a boat. So for the mantis shrimp to have only 6 metres of error per kilometer is actually quite significant.

Until now, it was believed that polarized vision was only used by marine animals to detect predators or for covert communication, such as in cuttlefish. This new study shows that, similarly to many terrestrial animals, marine animals have the ability to utilise polarization-sensitive vision for navigation and geolocalization.

Underwater polarization patterns are the result of mainly two optical phenomena; refraction and scattering. This model didn’t allow for the Sun to be lower than 40 degrees above the horizon, due to the colour of the sky. The colour blue refracts at 40 degrees, therefore was removed due to the large amount captured by the camera when the Sun coincidently dropped below the 40 degree angle.

Despite the many environmental factors that challenged this study, such as wind, waves and the colour blue, there is room for more research to help explain this very interesting scientific development.

 

Picture: Schematic of in-water polarization patterns. (A) The cylinder shows the polarization states that the detector observes, in false color. (B) Polarization states predicted by the single-scattering model, in false colour (see key at right), for Sun elevations of 10°, 45°, and 80° above the horizon. For clarity, lines oriented at the polarization angles are overlaid on the graphs. Neutral points in the polarization occur where the polarization state of the scattering event cancels that of the refraction (Powell et al., 2018).

Journal article:

  1. B. Powell, R. Garnett, J. Marshall, C. Rizk, V. Gruev, Bioinspired polarization vision enables underwater geolocalization. Sci. Adv. 4, eaao6841 (2018).

http://advances.sciencemag.org/content/4/4/eaao6841

 

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