Bioluminescence in mesopelagic squid: diel color change during counterillumination.

Two species of mesopelagic squid greatly altered the color of their bio-luminescence during counterillumination. The color change was triggered by changes in water temperature corresponding to those normally encountered by these vertically migrating animals. These squid can probably conceal themselves under the different colors of downwelling light that they encounter in their day and night habitats.