
Camouflage is a vital adaptation used by many different types of both aquatic and terrestrial animals. Normally we think of an animal blending in with its surroundings to protect itself from predators, but camouflage can also be used as an effective way of ambushing one’s prey as well. Even when limiting our discussion to marine animals, the variety of camouflaging techniques is pretty impressive.
What I’d like to do here is just take five examples of camouflaged animals and look at how this behavior has been fine-tuned to be best suited for each individual species’ lifestyle.
Flounders

Of all the camouflaged marine life, flounders are perhaps best known for this behavior. In fact, nearly every part of their anatomy contributes to their ability to blend in with the bottom sediments. Although it appears to be flattened top to bottom, like a stingray, a flounder is actually flattened side to side. The fish lives lying on its side and has both eyes on one side of its body. The best way to see that this is true is to look at the tail. All fish have vertical tail fins that move side to side as it swims, as opposed to the flukes of marine mammals which are horizontal and move up and down. Looking at the tail of a flounder you can see that it is horizontal. This can only happen if the fish is lying on its side.

So this flattened body plan allows the fish to settle down into the sand, but it still needs to be able to match the color and pattern of the sea bed. We can use our own dermal layer as an analogy to see how a flounder achieves this. In the lower layer of our skin are cells called melanocytes which produce a brown pigment called melanin when the cells are activated by sunlight. The melanin rises to the surface of the cells and produce what we call a tan. Of course, this whole process is involuntary.
Flounders undergo the same process in their skin, but in this fish’s case both the melanin production as well as the pigment’s migration is completely voluntary based on the surroundings. In other words, melanin is consciously controlled by the fish by simply seeing what’s around it. A blind flounder cannot camouflage itself. A while back I saw a great example of this after one of my flounders lost an eye in a fight. For the rest of its life one half of its body was perfectly camouflaged while the other half was always close but just a little bit off. Without full vision it just couldn’t quite get its skin pattern to match the sand. In the above image are some of my flounders that I keep in a tank with a half-white/half-black substrate. You can see which ones have recently crossed over to the other side (it takes these winter flounder about twenty minutes to completely go from black to white or white to black).
Toadfish

While a toadfish is unable to change the color or pattern of its skin, it is able to imitate an algae-covered rock pretty convincingly. When it’s young this coloration helps it to avoid larger predators. The one above is full grown and almost a foot in length. A toadfish this size doesn’t have to worry too much about getting eaten.
Toadfish are lying-in-wait predators. Rather than actively searching for prey they simply hunker down next to a stone and wait for unsuspecting prey - usually smaller fish - to pass by close enough to snap them up with the huge mouth. You can see the little fleshy tabs along the bottom jaw. These resemble bits of weeds and even wave back and forth with the currents. You can learn more about toadfish in this very early diary in this series.
Pipefish

And speaking of waving back and forth with the currents, the pipefish manages to achieve this effect with its entire body. These fish are related to seahorses and their camouflaging ability sort of combines the techniques of both of the preceding fish. My diary on pipefish is here.
Like seahorses and sea dragons, like the yellow one in the top image, pipefish are covered with overlapping and fused armor plates, which does provide protection but also severely limits their swimming abilities. So camouflage is vital if this little fish is to survive. Fortunately the long, thin body shape blends in perfectly with the eelgrass plants this species favors as habitat. They will often hover among the weeds in a vertical position (either head first or tail first) and allow themselves to be swayed back and forth with the water’s movements.
And like the flounder, pipefish can also control their pigmentation to better blend in with the plants. They are green when living in new growth and brown late in the year as the grass beds turn dark and start dying back. And again, the color change is controlled by their eyesight.
Spider Crabs

It’s not just fish that have evolved the ability to blend in with their surrounds, many invertebrates can do so as well. Spider crabs are especially good at this and have managed to cleverly overcome one big obstacle: The exoskeleton.
The shell of crabs is not actually living tissue, so there are no melanin-producing cells to control. So spider crabs, which are in a large family of crustaceans known as "decorator crabs", blend in with their surroundings by picking up debris such as stones, shells and algae, and actually sticking them on their backs.
The exoskeleton of these animals are covered by what looks like a fine layer of fur. Microscopically this fur actually looks like thousands of tiny coat hooks. By attaching objects to these little hooks the crab becomes virtually invisible from above.
Octopus

Finally, we have the octopus, who’s ability to change the color and texture of its skin is nothing short of astonishing. What’s unusual about this animal is that this color change not only allows them to camouflage, but is used as communication as well. Being very territorial creatures, being able to tell its neighbors when its angry, frightened or receptive to mating helps it to avoid confrontation with other members of its species.
Like the flounder, the color is controlled willfully by manipulating skin cells. In the octopus’ case these cells, called chromatophores, don’t just contain the brown pigment melanin, but also incorporate colored pigments like blue, yellow and red. But nothing I could write about the camouflaging ability of an octopus could compare with seeing one in action. Watch this:
Other diaries in this series can be found here.