Ocean Watch

Monday, April 27, 1998

Octopus is any color

it wishes or needs to be

"What color is an octopus?" a reader recently asked via e-mail. My reply: Whatever color it feels like being.

That may sound like a flippant answer to a simple question, but it's true. Octopuses can change color in the blink of an eye, blending so well with their backgrounds they're nearly invisible.

Once, during a dive on the sunken ship Mahi off Oahu's Waianae coast, my guide pointed to a small rusted object in the corner of a bulkhead. I squinted but saw nothing. I started to swim away.

"No, no, look," the diver gestured, turning me back and jabbing his finger toward the corner. Still I saw nothing.

Then he reached out and, to my astonishment, that piece of rusty junk came alive. It was an octopus, colored and textured to match the ship.

The diver handed me the creature, which wrapped its tentacles around my bare hands and arms as it checked out this new situation. I'll always remember the sensation of those little suction cups moving gently up and down my arm.

When another diver came by, I peeled the octopus off my skin and held it out to him. But this creature was no dummy. Seizing its moment to escape, the octopus shot out a cloud of black ink, then jetted back to the ship. As it swam, it flashed red, then white, then brown. In a second, the octopus had slipped into a deck puka and was gone.

Octopuses (and their close cousins the squids) can change color with remarkable speed because of color cells on their skin called chromatophores. These cells are sacs of colored pigment that expand or contract to create just about any color or pattern found on the coral reef.

When the color cells are relaxed, all their pigment is concentrated in a dot at the center. But when the animal needs quick camouflage or a diverting flash of color, muscles around the cell pull and stretch until the pigment is spread out.

In octopuses, such color cells come in red, orange, yellow, brown or black. The combinations of these hues are endless, allowing the creature to match most natural backgrounds.

Other special cells in octopuses' skin are called iridocytes. These act like prisms and mirrors, reflecting light into rainbows of colors. In some species, such as the highly venomous blue-ringed octopus of Australia and the South Pacific, these vibrant colors serve as a warning to would-be predators.

Besides being able to change color, some octopuses can also change the texture of their skin to match their surroundings. Tiny muscles surround folds of skin on these octopus bodies. The octopus can contract or relax them to change the roughness of its skin.

A picture in one of my books shows an octopus mimicking a sponge. I looked at that picture a dozen times before I could see the octopus.

A lot of folklore surrounds octopuses and their kin -- and for good reason. These creatures are as weird and wonderful as anything in a sci-fi film. Consider:

If an octopus loses an arm in a battle, it can grow a new one. Some octopuses can even cast off an arm on purpose to distract a predator, then grow another.

Sometimes, when an octopus releases a cloud of ink, the cloud is shaped like the creature itself. This is called a pseudomorph, meaning false body. Often the cloud fools a predator long enough for the octopus to get away.

Octopuses stun or kill their prey with poison delivered through a bite. Hawaii's octopuses don't have strong enough poison to kill people, but Australia's blue-ringed octopus does. A 1-ounce octopus of this species has enough poison to completely paralyze 10 people weighing 165 pounds each. This poison, called tetrodotoxin, is the same as that of pufferfish, served as fugu in Japan.