Category: General Article
Thursday, December 7, 2017
Summary: Many deep-sea animals are red in color to help them hide in the darkness, but in this blog Dr. Tammy Frank explains why so many are silver.
When we think about camouflage, we usually think about blending in to the background, something like a tomato hornworm happily chomping tomato plants. Its bright green body blends in perfectly with the green stems and leaves of the plant. Many animals living in the deep-sea spend their entire lives in the water – not at the surface and not on the ocean floor. With many hungry predators and nowhere for prey to hide how do they stay out of sight? These animals have come up with different methods of camouflage.
In other DEEPEND blogs, might have read about transparency or being black or red as kinds of deep-sea camouflage. There is another kind of camouflage found in the deep-sea — silver. As you can see in the photo of the hatchetfish below, it has silvery side s like a mirror.
How does it work? Any light blocked by the fish’s body is reflected back into the eyes of the predator. You can see how this works by putting a mirror on its side in a sink full of water. If you think of the mirror as the fish, you’ll see the mirror side pretty much disappears as it reflect the other side of the sink.
Now, that works great during the day. But what about at night? Many deep-sea animals have photophores. Those are light producing organs. Many have them under their eyes to send out blue light. When they use this at night, and hit the mirrored sides of the fish, the blue light reflects back to the predator’s eyes. That makes the poor mirrored fish very easy to find. But, don’t worry. The mirrored fish know this is a problem and have come up with an elegant solution. They have “melanophores.” Those are little sacs of black pigment. At night, these melanophores expand and make the sides of the fish less shiny.
During the day, when the fish wants to be more like a mirror, the melanophores contract You can see the contracted melanphores in the hatchetfish photo.