The world seems cloaked in an array of tones of gray: light gray skies, dark gray streets covered in gray mud, and my car — which used to be blue — is now also gray from mud. Looking out my office window, I see a gray ocean sometimes whipped into patterns of white wave crests.
Sometimes I pull out the red pants or the bright orange sweatshirt simply to signal my presence in this sea of gray. Sea of gray? What does it look like in the sea? How do fish and other sea animals see the world of colors — or the lack of colors?
As I was curious about the topic of colors in the sea, I came across a graphic that showed the predominant coloration of animals at different depths in the ocean. At the surface, most animals were blue. In the top layers below the surface, most animals were blue on top but white or silvery from below. Deeper down, there were a lot of transparent animals, some of whom had red stomachs.
Red became more dominant at depths where sunlight does not penetrate. In the lightless deep ocean, animals were either red or black, and many can produce light through a process called bioluminescense.
Considering these color schemes, it becomes evident that the color of animals at sea has everything to do with camoflage. Unlike my orange sweatshirt, which shouts “here I am,” the red color of deep-sea animals does not show up against the abyssal darkness unless light is directed at it.
Toward the surface, where some light penetrates, animals are subject to predators from above and below. From above there are birds; from below there are other fish, including sharks and marine mammals on the hunt. Where do you hide from these predators when all around you is only seawater?
The answer is countershading. A white belly can blend in with light from the sun when a predator approaches from below. From a bird’s perspective, a dark bluish back in the sea is difficult to make out. In addition, most animals swarm in these surface regions, hiding them in the crowd.
As light enters the ocean, some of it is reflected off the water surface. The light beams that enter the water are refracted, which means they change direction slightly. If you ever wondered about the light of a rainbow, you know that light can have different colors and those colors have to do with the wavelengths of the light.
Red light has the longest wavelengths and the lowest energy, while blue light has much shorter wavelengths and much higher energy. Sending light through water — about 800 times thicker than air — takes energy. Thus, blue can travel further through the water than red. This is why we can’t see the red color more than a little ways down, but underwater pictures are usually all blue.
Fish have especially adapted eye lenses to see underwater. Their eyes see more detail in the world of blues. It has been found that fish in deeper regions of the ocean have a different lens and thus different vision that those that spent their lives closer to the surface.
The most complex eye known in the animal kingdom belongs to the mantis shrimp, an inhabitant of tropical waters. This eye features over 16 different photoreceptors and over 10,000 ommatidia (clusters of photoreceptor cells), organized in three distinct regions of the eye. Mantis shrimp can see in the ultrviolet sprectrum, which means they can see heat waves. Researchers can only guess at how the shrimp use this ability, but one thought is that they can send secret messages to potential mates.
The ocean may be gray on the surface, but below there are uncountable wonders and creatures with amazing abilities. As my eyes begin complaining from computer strain I can close them a little and dream about the colors of coral reefs, in which fish in yellow and orange show off or hide amid the colors of the coral.
Switgard Duesterloh Ph.D., is an assistant professor of natural sciences at Kodiak College. She operates the Kodiak Ocean Science Discovery Lab and teaches ocean science to students throughout the Kodiak Island Borough School District.