Cephalopods are the most intelligent invertebrates in the world.
By Devin Murphy
“Most people don’t think of invertebrates as smart,” says Alan Peters, the National Zoo’s invertebrates curator. Perhaps it’s time to think again, with minds stretched by a visit to the Invertebrate Exhibit. There, you’ll encounter two famously smart species: the giant Pacific octopus and the common cuttlefish.
They are among more than 700 species in the class Cephalopoda, a group that also includes squid. These marine animals tend to have soft, fleshy bodies; tentacles or arms; keen vision; and hard, birdlike beaks. Some have shells; many don’t. They move by jet propulsion, squirting water through tubes known as siphons. Their brains, roughly the shape of doughnuts, are the largest of any invertebrates.
Common cuttlefish (Jessie Cohen/NZP)
Keeping those big brains busy can be a challenge for Zoo staff. Cuttlefish and octopuses are capable of learning and retaining information. They can solve puzzles and navigate mazes. Experiments with cuttlefish and octopuses have shown that they can learn to navigate a maze with more than one exit by interpreting simple visual cues, such as a purposely placed object. They can remember which object is associated with which exit and which direction to swim to the exit.
Such intelligent animals need plenty of activity to keep them stimulated. Keepers maintain a varied schedule of enrichment exercises. Octavius, the Zoo’s giant Pacific octopus, has an enrichment program that encourages his natural curiosity. Keepers regularly switch enrichment items so he does not get bored. Since he is capable of learning, keepers give him puzzles to figure out. He may have to manipulate a toy, box, or jar a certain way to get a reward hidden inside.
Giant Pacific octopus (Mehgan Murphy/NZP)
Biologist Tamie DeWitt carefully observes the reaction Octavius has to each enrichment object. She is looking for any preference that Octavius has—for, say, a red toy or a blue one. That information helps keepers design an enrichment program that is especially stimulating for him.
Octopuses’ natural inquisitiveness does not end with objects in their tanks. “The most interesting thing an octopus can do is get out of its tank,” says DeWitt, “but that’s usually a very bad thing.” These skilled escape artists can get out of their tanks easily if a lid is not secured properly or they are provided with even the smallest opening.
The Zoo takes extra precautions to ensure that Octavius cannot slide open the top of his tank and escape. Since the only hard part of his body is the beak, which is about the diameter of a quarter and hidden behind his arms, he can fit through any space that is larger than a quarter.
Although octopuses can survive out of water for short periods of time, they risk death if they venture out of their environments. “Usually if they are going to get out of a tank they’re not going to be able to make it back and survive,” explains DeWitt. Even if an octopus made it to another tank, the animal could not survive in water that is not the correct temperature, chemical composition, and pressure.
Playing With Food
Keeping cephalopods engaged—and in their tanks—is only part of the challenge of looking after these intelligent animals. Feeding them is another. Being predators, cephalopods crave live prey. In the wild, they pounce on food—snatching it with their tentacles and gobbling it up.
This means keepers cannot simply dump crayfish into cephalopods’ tanks. The animals will not search the bottom, looking for scraps of food. Zoo staff need to make sure that cephalopods see and smell food—and eat it right away. Otherwise, it falls to the bottom and decomposes, contaminating their water.
Young cuttlefish flatly refuse to eat anything but live prey, so the Zoo obtains it for them. Doing so is a logistical nightmare, however, so keepers wean the young cephalopods as soon as possible. “When they grow up, we train them to eat frozen prey from a stick. It can take hours and hours, and that is why we love our volunteers,” says DeWitt.
Feeding time for a young common cuttlefish (Jessie Cohen/NZP)
The hardest part about feeding the juvenile cuttlefish, weaned off of live prey, is finding them. The cuttlefish camouflage themselves and hide among the pebbles in their tanks. To spot them, keepers look for the distinctive, silvery, W-shaped eyes that protrude slightly from the pebbles. They then dangle a succulent piece of shrimp on a stick, luring the cuttlefish to shed their masterful disguises.
Cuttlefish have excellent eyesight, and when they see their food, they emerge from their hiding places. After they have readied themselves to attack, they strike. They seize their food with their tentacles and pull it into their beaked mouths.
Chambered nautiluses hunt in the wild by gliding shell-first through the water. They sweep prey into their mouths with their tentacles. At the Zoo, they react instantly to the smell of shrimp in their tank. As the nautiluses move around excitedly, keepers literally hand-feed them, holding pieces of frozen shrimp within reach of a nautilus’s tentacles until the animal grabs and eats the shrimp. While doing so, keepers take care to keep their fingers away from the cephalopods’ sharp beaks!
The Zoo’s giant Pacific octopus is not quite so coddled when he is fed. Feeding time is also playtime for Octavius. Like cuttlefish, octopuses are extremely intelligent and curious. They have excellent eyesight and smell, so keepers make them work for their food. A tantalizing shrimp on a stick is just the ticket.
“We shake the stick so he thinks it’s a live piece of prey,” says DeWitt. “His natural instinct is to grab it and hold on to it.” Octavius then plays a game of tug-of war with the keeper. “You will never win a tug-of-war with an octopus,” says DeWitt of the game. So when keepers give up, they relax the stick. That signals to Octavius that it is time to let go.
Disguises in the Deep
How did cephalopods get so smart? One theory has to do with the fact that many of them, such as octopuses, cuttlefish, and squid, do not have shells. That meant their brains had room to grow. Another theory is rooted in cephalopods’ remarkable camouflage abilities. Changing their appearance at will requires a huge amount of brainpower.
The enrichment program for the cuttlefish is designed to let them use their unparalleled camouflage skills. Cuttlefish are very responsive to stimuli, so keepers have an arsenal of things they can do to get their colors flashing. “We put objects in the tank,” says DeWitt, “like plants and tunnels and corals. And sometimes we do different lights around the tank, like Christmas lights. Sometimes we’ll put pictures in there, or a hamster ball with live crayfish.”
In the wild, camouflage acts as a defense mechanism. Rather than solely relying onthe cover of an ink cloud (squid, octopuses, and cuttlefish have ink sacs) to escape predators, cephalopods depend on their ability to change their appearance in seconds.
Octopus and cuttlefish skin is covered in chromatophores, or bundles of pigment. They contain red, yellow, orange, black, and brown pigments. Controlled by nerves, chromatophores are activated when muscles contract. Color spreads out across a cephalopod’s entire body.
Cephalopods have other camouflage tools too. Their skin is also covered with iridophores, which reflect colors in the environment. Cephalopods can also change the texture of their skin with tiny projections called papillae. They make the animal resemble a rough surface, such as hard coral. Ironically, given cephalopods’ painterly use of color, the animals are themselves color-blind.
In addition to their defensive duties, colors and patterns play important roles during breeding. Take cuttlefish, for example. They live only about a year, so breeding is a very intense and important time. At the Zoo, cuttlefish are housed together only when they are very young or for breeding. But after mating, keepers separate males and females. “It can be pretty quick,” says DeWitt of the time cuttlefish are put together to breed. “We usually don’t leave the male and female in together because he’ll just harass her.” The Zoo has bred three generations of cuttlefish and currently has four juvenile cuttlefish.
Chambered nautilus (Mehgan Murphy/NZP)
In the wild, having such a short time to pass on genes makes breeding a coveted activity. Colors and patterns help cuttlefish communicate with each other when they are ready to breed. Breeding often involves competition for mates, which can require a male cuttlefish to say two things at once: “Keep away!” to other males and “Pick me!” to females. “It can literally split its body in half and change colors, presumably warding off one and attracting the other,” says Peters.
Even without male competition, the mating display is still a colorful sight to see. “It’s the patterns,” explains DeWitt. “The male, he spreads himself out to make himself look real big and does a real distinct zebra pattern. He does this thing called a passing cloud where he takes this stripe and spreads it out along his entire body. It looks really neat.”
If a male cuttlefish is not large enough to impress a female, he still has another option for wooing her. Large male cuttlefish guard their potential mates from other males, but cuttlefish are masters of disguise. A smaller male may try slipping past an aggressive larger male. “Sometimes the male will try to look like a female so he won’t have to do the bright colors and sparring behaviors, and take the aggression of another male,” explains DeWitt. “He’ll just be subservient.”
While under the guise of an unassuming female, the smaller male will approach the guarded female and mate with her. He can then slip away without the larger male ever becoming the wiser. There is evidence that females favor such resourcefulness and choose to fertilize their hundreds of eggs with packets of sperm passed to them from cross-dressing males during mating rather than the sperm of larger males.
Other cephalopods are harder to breed in captivity. In all the years the Zoo has had octopuses in its collection, a female has only laid a clutch of eggs once, and they were not fertile. Also, octopuses are solitary animals. There is no definite way for keepers to predict what will happen if two octopuses are put in the same tank. “They mostly live on their own and when you put them together, they may mate or they may fight,” says Peters.
The chambered nautilus has never been bred successfully in captivity. “We have had nautilus eggs, but we have not successfully hatched them out,” says Peters. Scientists have also not been able to collect much information about how nautilus eggs are laid and develop in the wild because they have never been observed in the wild.
Cephalopods in the Wild
The precise status of many cephalopods in the wild is not known exactly, but these invertebrates are not believed to be under any imminent threat. The giant Pacific octopus, common cuttlefish, and chambered nautilus are not classified as endangered or vulnerable. “Right now I think they are more collected for food and shells,” says Peters.
Their stable status means that there are plenty of opportunities to learn more about these intelligent, spineless wonders in the future. New species are still being discovered in deeper, less accessible waters, adding to their mystique and intrigue. Watching the cephalopods at the Zoo, it is easy to wonder: Is the ocean still concealing its most intelligent cephalopod?
—DEVIN MURPHY was an editorial intern for Smithsonian Zoogoer.
If you have a comment about Smithsonian Zoogoer magazine, please email it to us.Smithsonian Zoogoer 40(4) 2011. Copyright 2011 Friends of the National Zoo. All rights reserved.