Kraken: a new book about squid
Here’s an exclusive excerpt from the nature book, Kraken: The Curious, Exciting, and Slightly Disturbing Science of Squid, by Wendy Williams.
One of the biggest problems cephalopods face is how to live safely in a 3-D world. When you imagine swimming in the deep ocean, you have to rethink human-oriented concepts of “up” and “down.” As rather large surface animals who live on the continental crust, we usually need only be aware of animals living on the same plane that we do: Will we be attacked by a lion? Trampled by an elephant? Usually, “up” and “down” are not words that hold terror for us. We don’t fear giant birds swooping down from above to scoop us up and carry us away, and we don’t fear giant worms bursting out of the earth’s crust to grab us and drag us underground. We only need to be aware of enemies that, like us, are firmly rooted to life atop the soil.
But surviving in the ocean is more complex. An animal living in the sea needs to have the responses and defenses of a fighter pilot. The enemy can come from anywhere, from the left or from the right, but also from above or from below. It’s a three-dimensional world down there. Skeleton-free cephalopods are particularly at risk, since predators don’t need to worry about the bones. “The creatures are really just rump steaks swimming around,” Australian scientist, Mark Norman once explained. They need special protection.
In response, the animals have evolved an impressive tool kit of tricks. Bathyscaphoid squid, named in honor of a self-powered sea exploration vehicle that was developed after the 1930s bathysphere of naturalist William Beebe, is a family of squid that spends its early life, when it is most vulnerable and most likely to turn into someone else’s dinner, at the ocean’s surface, where there are plenty of small tidbits for a tiny animal to eat. As the Bathyscaphoid squid develop, they descend deeper and deeper into the water. These squids have evolved a body that’s translucent and nearly completely invisible. At the top level of the ocean, the water’s rich with nutrients. It’s easy for them, as predators, to find food. Unfortunately, it also easy in the sunlight to become pretty to other predators. But with a body that’s almost transparent, these young squids are ghostlike, nearly invisible. Being nearly invisible when tiny is quite convenient. The young squid at the sea surface can easily sneak up on its even tinier prey without being noticed. A prey animal might perceive what seems to be a twinkle of sunlight at the sea surface, only to find itself enveloped in a mass of squid arms and tentacles.
Locating your enemy in the ocean is a 24/7
task. Color and luminosity are both armor and weaponry. Many
animals developed the ability to change shape and color to
blend in with their surroundings. Some fish can do this, as can
some frogs and, of course, chameleons. But no group of animals
is as sophisticated in this strategy as are the cephalopods,
nature’s best now-you-see-them, now-you-don’t masters of quick
change. When we watch these animals zip through a myriad of
psychedelic displays in only seconds, we stare, transfixed. But
the basic organization of this magic show is simpler than you
might think: It’s done with three layers of three different
types of cells near the skin surface — a layer of
chromatophores, a layer of iridophores and a layer of
The top layer of cells, the
chromatophores, contains the colors yellow, red, black, or
brown. The colors present are species-dependent. The color in a
chromatophore cell sits near the cell’s center in a tight
little ball with a highly elastic cover. When the muscles
controlling the chromatophore are at rest, this ball of color
is covered over and can’t be seen. When a chromatophore is
showing, what you’re seeing is this little ball, stretched out
into a disk roughly seven times the diameter of the at-rest
To operate properly, one chromatophore cell has
a number of support cells, including muscle cells and nerve
cells. The arrangement is cunningly elaborate. Anywhere from
four to twenty-four muscle cells might attach to only one
chromatophore. When these muscles contract, pulling on the
chromatophore cell, the elastic sac is stretched out, revealing
the color inside. When the muscles relax, the ball returns to
normal size and the color disappears. There’s a simple way to
envision this: Imagine a small, circular sheet of red paper.
Crumple it into a tiny, tight ball. The color red is now only a
pinpoint. Using your hands — and the hands of up to eleven
other people if they’re around to simulate the twenty-four
muscle cells — stretch the paper out so that it’s flattened to
its full size. Then crinkle the paper into a tiny ball again.
Do that umpteen times a second, to simulate flashing. On an
infinitely smaller scale, that’s how a cephalopod operates one
This is enormously elaborate
engineering, requiring a considerable amount of coordination
and support. The muscles surrounding the color-containing cells
are controlled by nerves that interact with other nerves. Some
scientists think that this complicated system may be one
explanation for cephalopod intelligence, since the system
requires the interactions of so many neural cells.
Just below the layer of chromatophores is another
layer of cells, the iridophores. This layer of cells shows a
different array of colors — metallic blues, greens, or golds.
The iridophores do not open and close. Instead, they reflect
light. They are sometimes used to camouflage an animal’s
organs, like eyes, by shimmering and drawing attention away
from the organ. Some scientists have studied this strategy as a
way to improve camouflage for soldiers on the battlefield.
Underneath this layer is the final layer, a layer of
leucophores, flattened cells that passively reflect the color
of background light, increasing the animal’s camouflage. When I
first watched cephalopods showing off their artistic genius,
some of their techniques seemed familiar. I knew I had seen
this use of color and light somewhere else. Then I remembered
Claude Monet’s many paintings of water lilies, of haystacks,
and of a cathedral at Rouen. Monet could paint the same scene
many times, but each painting is different because the master
could so expertly show the differences created by only slight
shifts of light.
Cephalopods are the original
Impressionists. I often wonder if the French painters didn’t
quietly study the cephalopods’ techniques. Both the
Impressionists’ and the cephalopods’ light shows provide the
illusion of great depth by using luminosity — the reflection
of light. Both skillfully use thousands of points of light and
color to trick the observer.
But not all cephalopods
enjoy equal artistic talent. Cuttlefish, which live nearer the
ocean’s surface where light still penetrates, are outstanding
in their Impressionistic skills. Humboldt squids, on the other
hand, are quite limited. With their highly honed predatory
abilities and their large size, they don’t need to devote so
much energy to disguising themselves. Moreover, since so much
of their lives is spent in dark ocean depths, all the Humboldt
needs is red chromatophores, which allow it to disappear
Roger Hanlon, a cephalopod researcher at
Woods Hole’s Marine Biological Laboratory, is studying
cephalopod camouflage abilities that may have military
applications, along with the Air Force Research Laboratory in
Dayton, Ohio. Recently, the Department of Defense awarded the
MBL scientist $1.2 million for a study of “Proteinaceous Light
Diffusers and Dynamic 3-D Skin Texture in Cephalopods.” The
Ohio lab is studying some of the proteins involved in
cephalopod camouflage, to see if some of those proteins might
somehow be used to help soldiers become less visible on the
2011, Wendy Williams. Reproduced by permission of the
publisher, Abrams Image.