QUESTION:
Do krill really glow in the dark at sea?  How do they do this?  How would
this help them survive?

        Fourth Graders in Ms. Heisler's Class
        Meeker Elementary School
        Greeley, CO, USA



ANSWERS from Karen Haberman, Antarctic Research Team
            Palmer Station, Antarctica
            Wed, 26 Feb 1997 03:40:53 -0500

Dear Students,
 
Yes, krill really do glow in the dark.  They have photophores
("light spots") along their sides, their ventral surface (facing
downward), and beneath their eyes.  These photophores produce a
blueish-purple light using a special chemical reaction common to many 
light producing animals. It is quite beautiful to see.  

It is not fully understood why many marine plants animals glow in the 
dark.  Generally, they only glow when disturbed, for example when 
they are approached by a predator, so some scientists think this 
glowing serves to startle the predator.  Another idea is the "burglar 
alarm" hypothesis.  It is also possible that glowing in the dark 
allows them to somehow communicate with each other, perhaps as a 
warning system that can spread throughout a krill school.

Thanks for your question!
Karen