Marine biologists and physiologists have now discovered at least one use for these eyes in the deep, blue ocean: to see the fluorescent markings mantis shrimp use to signal or threaten one another.
The shrimps' characteristic spots are easy to see in shallow water but only dimly visible 40 meters (131 feet) down, so on the ocean floor the crustacean's spots fluoresce yellow-green to enhance their prominence in the dim blue light.
Though fluorescence in marine animals is common - in corals and squid, for example - this is the first documented case of fluorescence used in signaling in the sea. Fluorescence occurs when a pigment absorbs one color of light, in this case blue, and emits a different color, such as yellow-green.
"If you look at this animal in shallow water or in bright white light, you pick out this set of yellow-green spots it uses in species recognition, and probably in mating as well - it's a typical signal that says, 'Here I am, I'm a Lysiosquillina glabriuscula,'" said marine biologist Roy Caldwell, professor of integrative biology at the University of California, Berkeley. "But this animal also occurs at 40 meters, where there's no yellow light for that pigment to reflect, so that species-specific signal should be gone. But when you go down to 40 meters and you look at it, the yellow spot is still there."
"The stomatopod (or mantis shrimp) apparently is using a yellow-green fluorescence to maintain visual constancy of a species-specific signal," Caldwell said in a phone interview from Brisbane, Australia, where he is on sabbatical.
Caldwell and coauthors Charles Mazel of Physical Sciences Inc. in Andover, Mass., Thomas Cronin of the University of Maryland, Baltimore, and Justin Marshall
Contact: Robert Sanders
University of California - Berkeley