Many animals have evolved camouflage, but nobody quite pulls it off as beautifully as the octopus and its tentacled cousin the cuttlefish. These invertebrates, which belong to a group called cephalopods, are covered in microscopic pigment organs that they can squeeze and stretch to take on the patterns around them. They can curl their tentacles to assume different shapes, and they can even change the texture of their skin to bumpy or smooth, as necessity demands.
Nobody knows the tricks of cephalopods better than Roger Hanlon, a biologist at the Marine Biological Laboratory in Woods Hole, Massachusetts. As I wrote in this New York Times profile of Hanlon, he has documented their powers of disguise both in the wild and in his lab. You can see some of the cephalopods in action in this Times video I narrated, as well as in these videos at Hanlon’s web site. Hanlon has carefully documented how cephalopods can melt away into their backgrounds; he’s also shown that male cuttlefishes can disguise themselves as females to sneak past bigger males to get a chance to mate. There’s still a lot Hanlon has yet to study about cephalopod camouflage, though; many of the most spectacular displays of shape-shifting are one-offs that Hanlon or a wildlife videographer happened to catch on a few seconds of video.
The video shown here is the latest addition to the repertoire of cepahlopod camouflage. As Hanlon and his colleagues write in a paper to be published in Biological Bulletin, the Atlantic longarm octopus (Macrotritopus defilippi) does an uncanny impression of a flounder.
Hanlon first saw this trick before he actually knew what it was. In the early 1980s, he captured a young Atlantic longarm octopus and reared it in a tank at Texas A&M University. It was the first time anyone had ever paid close attention to the biology of this obscure creature, which lives on sandy expanses of the Caribbean sea floor. While observing the octopus, Hanlon noticed that sometimes it would flatten out its tentacles and swim close to the bottom of the tank. At the time he didn’t know what to make of it.
In 2000 wildlife photographers took pictures of Atlantic shortarm octopuses in their natural habitat and suggested that they took on the strange shape to mimic flounders. Four years later, Hanlon took another picture that showed the octopus not just flat against the sea floor, but assuming the pattern of the surrounding sand–a trick that flounder use as well. The next year Hanlon and his colleagues spent 51 hours diving of the coast of the island of Saba searching for the octopuses on the sand plains. They managed to film one animal apparently pretending to be a flounder. And since then, professional photographers have supplied Hanlon with still more videos.
Hanlon and his colleagues have compared the footage of the octopus to footage of the peacock flounder, which lives in the same waters. The similarities are uncanny. Flounders hug the sandy bottom as they swim, even following the sand’s ripples. So do octopuses. The octopuses swim in the same short bouts as the flounder, and at about the same speed. They form their tentacles into a sheet-like mass with the same body outline as the flounder. The big difference between the octopus and the flounder is the way they blend into the background. The flounder are relatively slow at matching their surroundings, while the octopuses can change their skin quickly and with great precision. If there are white rocks scattered around on the sandy plain, Hanlon has noticed, a stationary octopus will produce a white spot on its body as well.
The Atlantic longarm octopus is not the only octopus to pretend to be a flounder. On the other side of the world, off the coast of Indonesia, Hanlon and his colleagues have documented two other species that pull off the same trick. (Here’s a video of one of the Indonesian species.) Pretending to be a flounder is such a useful strategy that three distantly related species of octopus have independently evolved it.
With flounder-mimicking octopuses now firmly established in the Atlantic Ocean as well as the Pacific, it’s high time to ask what is so great about flounders? Sandy plains are dangerous places for soft-bodied octopuses. Predators can spot them as they move across the open expanses. It’s possible that octopuses are not mimicking flounders per se, but are just taking advantage of the same kind of camouflage. But it’s also possible that small fish that do spot the octopus may leave it alone because it looks like a flounder. While a small fish could easily take a bite out of a soft, fleshy octopus tentacle, a tough, scaly flounder would pose a threat.
February 24th, 2010 at 2:00 am
I’ve wondered what the adaptive value of flatfish mimicry is for Thaumoctopus before and considered that it might just be convergent cryptic behavior. It seemed hard to thing of a predator that would go after a large octopus but avoid a flatfish.
Not knowing anything about their social structure, I wonder if they might be trying to evade the notice of con-specifics to avoid territorial aggression or unwanted sexual advances? Hadn’t considered the “small fish” angle before, however, that’s an interesting suggestion.
February 25th, 2010 at 2:34 pm
There are several octopuses that live on open sandy bottoms that move in a similar manner. Thaumoctopus and the long-armed Atlantic species are just two examples. Keeping low, pressed against the substrate to avoid detection certainly may be one reason, but we should also consider the hydrodynamic advantages of such movement as another convergent force shaping both flat fish and octopuses.
February 25th, 2010 at 6:52 pm
Neil — The answer to your question might be that flounder are bony and octopi are not. We fish for fluke (summer flounder) on the south side of Cape Cod and they are big: the local expression is “doormats.” But they have a fully rigid, bony skeleton. An 18″ long fluke is about 12 inches wide. The biggest predators are large striped bass and bluefish, which would have a very hard time getting a good-sized flounder in their mouth. In contrast, because squid and octopi are soft-bodied, they are an easy bite for bigger predators, even if they are big. But if a squid or octopus makes itself look just like a fluke, esp. a doormat, larger predators like stripers and blues or tuna will more likely move along in search of easier to swallow prey.
The use of sharp, stiff bone structure to deter predation is well established in fish like bullheads (hornpout), yellow perch and the sunfish/black bass family. Make yourself hard and painful to swallow.
In this sense the octopi imitation of flounder might be like viceroy butterflies mimicking monarchs.
February 26th, 2010 at 4:01 am
I’ve been fascinated by octopi for a while, and I remember seeing footage of an octopus camouflaging itself. It was in an area of flat sandy seabottom dotted with black plants that had curving leaves. The octopus turned itself black and arranged its tentacles in the exact same shape as the plant’s leaves, and swayed with the current in the same way. Even to human eyes, it was almost indistinguishable from the plant.
Cool animals.
March 4th, 2010 at 11:54 pm
I suspect Roy is correct…I think this is less an instance of flounder mimicry and more an instance of Sand Mimicry producing convergent solutions. Moving along the seafloor in such a way as to quickly camouflage oneself has certain requirements.