Imagine this scene.

     It is a moonlit night in the Hawaiian Islands.  A bobtail squid is gliding along through shallow waters.  But despite the moonlight, the squid casts no shadow on the seafloor as it swims.  Why not?

     Since a moving shadow in the moonlight could alert the squid’s predators to the animal’s presence, this creature has evolved an incredible mechanism to avoid casting a shadow.  When darkness alone won’t serve to hide the squid, it produces its own light, which shines downward onto the seafloor.  The squid can even modulate the brightness of the light it generates, so that it matches the intensity of the surrounding moonlight on the seafloor!

     How is the squid able to protect itself in this amazing way?

     Scientists have discovered the squid’s secret.  The bobtail squid has a bioluminescent organ on its underside.  Inside this organ is a population of bacteria that glow in response to changes in oxygen concentrations in the squid.  Inside cells around the bioluminescent organ, as well as in cells in the skin, ink sac, and around the eyes, are reflective, iridescent structures, called platelets, that reflect the bacterial light. 

     While many aquatic creatures can reflect light, they cannot modulate their light to match surrounding light, as the bobtail squid can.  The platelets of these other light-reflecting animals have a rigid structure that does not allow for changes in reflectivity.  The squid’s platelets, however, are made of flexible protein structures that allow the animal to alter its reflectivity.   Hence, the bobtail squid’s ability to match its own downard shining light with the intensity of the moonlight shining on the seafloor.

     Amazing, huh?– April Moore

Hawaiian bobtail squid

 

 

 

 

   

This entry was posted on Tuesday, April 20th, 2010 at 8:42 am and is filed under Insights and Visions on the State of the Earth. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.