A Living Light Show Beneath the Waves
Finning his way along the base of a rocky ledge, a scuba diver saw a two-foot- [60 cm]long cuttlefish hovering in a recess, almost perfectly camouflaged in its blue-gray surroundings. When the diver got closer, the cuttlefish flushed a brilliant, shimmering crimson. When he backed off, it returned to its original color. Have you ever wondered how these amazing mollusks accomplish that feat—an ability they share with certain species of octopus and squid?
Their secret lies in chromatophores, pigment-bearing cells in the skin. Nerves cause muscular contractions that regulate the size of these cells, thus causing the creature to vary its color and create changing patterns of color.
In addition to controlling color, many species of squid even produce their own light, doing so in a way similar to that of the common firefly. This bioluminescence, which is seen in many other marine creatures—from jellyfish to shrimp—results from complex chemical reactions in cells called photocytes or in organs called photophores. It can also result from the activity of luminous bacteria that enjoy a symbiotic relationship with their host.
In the former case, the light-emitting cells and organs contain a chemical called luciferin, which reacts with oxygen in the presence of an enzyme, creating light that is usually blue to green in color. Some luminous organs, says the journal Scientific American, “are elaborate devices with lenses for focusing, a color filter, or an adjustable flap that serves as an off/on switch. Squid that have both photophores and chromatophores within their skin can control both the color and the intensity of light produced.”
Creatures that glow by employing luminous bacteria accommodate their microscopic guests in special light organs, which are endowed with a rich supply of blood. The blood carries nutrition to the microbes, in effect paying the “light bill.”
[Picture Credit Lines on page 31]
Inset: Courtesy Jeffrey Jeffords/www.divegallery.com
© David Nicholson/Lepus/Photo Researchers, Inc.