Ever wonder how fish camouflage themselves in the open ocean? Researchers believe they found one piece of the puzzle; specialized nanocrystals in their skin allow them to blend in against a background of polarized light.  Human vision can interpret colors that vibrate and travel through different planes; however, humans cannot see polarized light because it travels in one plane that our vision can’t understand.  There is a growing body of research to support the theory that many different types of marine animals see polarized light and have adaptions based on this ability.  For example, the mantis shrimp uses polarized light to detect other mantis shrimp, evade predators and attract mates. A unique phenomenon occurs in the ocean when visible light breaks through the water’s surface – it becomes polarized.  Researcher, Dr. Molly Kummings, claims that what seems to be an open blue expanse to us, “would probably look something like walking through a kaleidoscope” to marine life who see polarized light. perper4

The recent study published in Science was conducted by Dr. Kummings and Dr. Brady, in order to compare two fish species in the open ocean to two species inhabiting coral reefs, all part of the Carringidae  family.  The Carringidae family includes small schooling fish, such as: mackerel, jack, scad, and pompanos. The goal of the study was to understand how seemingly vulnerable fish survive in the open ocean, and compare their behavior to the coral reef fish.  In order to do this, Dr. Brady built a video polarimeter, which it senses information about the polarized light field while rotating around a live fish specimen.  The 360 degree rotation of the camera showed how much the fish contrasted with the polarized light, at a variety of different angles.  It was basically testing how well the fish camouflaged itself into the polarized light.

Additionally, the researchers examined the platelets, or small skin cells that are responsible for the silvery shin of a fish’s skin.  They noticed that the color produced by these platelets directly correspond to their pattern and arrangement.  It was found that open-ocean species had hexagonal platelets that were aligned parallel to the gills and wrapped around the fish’s entire body.  Dr. Kummings believes that this pattern makes them extremely well camouflaged when viewed head on and from behind, thus could help them avoid becoming someone’s next meal.  The overarching conclusion the researchers developed was data from the video polarimeter confirmed that open ocean species, “minimize contrast with their polarized background” making them well camouflaged, while coral reef species instead were highly visible against the polarized background.  From an evolutionary standpoint, it appears that this adaption of aligning platelets to camouflage against polarized light originated from a common ancestor, but when it was no longer needed to survive life on a coral reef those fish lost it, while open ocean species retained this unique adaption.  So what may look like a fish standing out in an expanse of open ocean to the human eye, could actually be a perfectly camouflaged fish in the eyes of its predator.

Pompano Courtesy of: catchingfish.com

Pompano
Courtesy of: catchingfish.com

Military Applications?

To add another intriguing layer to this research project, it was funded by the United States Navy, “for finding biological phenomenon that may have military applications”.  Though the researchers are not permitted to disclose the possible applications, it is not hard to imagine how this information could benefit the military.  It is often said that nature already fixed all our problems, and the secret to open ocean camouflage could lead to advances in Navy technology.  One possibility, is that the submarines could be equipped with patterns that mimic those naturally occurring in fish, making them harder to detect at sea.  Additionally, more and more research is done on how different marine life perceive the world they live in, and how polarized light could play a vital role in many species ability to survive.

 

http://www.pbs.org/wgbh/nova/next/nature/open-ocean-fish-camouflage-themselves-with-rotating-crystals-embedded-in-their-skin/

http://www.bio.utexas.edu/research/cummingslab/pdfs/Brady-Science-2015.pdf