Three Hearts and Blue Blood: The Strange Life of the Giant Pacific Octopus

A giant Pacific octopus has three hearts and blue blood. That sounds like something from science fiction, but both facts come from the same everyday problem: getting enough oxygen out of cold seawater.

The giant Pacific octopus, Enteroctopus dofleini, lives in the cold waters of the North Pacific, from California up to Alaska and across to Japan. It is the largest octopus species we know of, and its life is one of the strangest in the ocean.

Why three hearts, and why blue

Two of an octopus's hearts pump blood through the gills, where it picks up oxygen. The third pumps that oxygen-rich blood around the rest of the body.

The blue color comes from hemocyanin, a copper-based protein that carries oxygen. Our blood uses hemoglobin, which is built around iron and turns red. Hemocyanin turns blue when it picks up oxygen, and it works well in cold water with little oxygen in it, which is exactly where this octopus lives.

From a grain of rice

A giant Pacific octopus starts life tiny, about the size of a grain of rice. The hatchlings drift in the open ocean as part of the plankton for weeks or months, and very few survive. The ones that do settle to the seafloor and start to grow fast. An adult can reach well over 30 pounds, with arms that span several feet.

A body that thinks in its arms

An octopus can change color and texture in a fraction of a second, using thousands of color cells in its skin called chromatophores. It uses that to hide, to hunt, and apparently to signal mood.

Its nervous system is just as unusual. Roughly two-thirds of an octopus's nerve cells are in its arms, not its head. Each arm is lined with suckers that can both touch and taste, and the arms can react to what they find without waiting for orders from the brain. Most of that research comes from the common octopus, but giant Pacific octopuses are built the same way.

And because the only hard part of its body is its beak, an octopus can squeeze through any gap its beak can fit through. Aquarium staff learn this the hard way.

The long wait

Giant Pacific octopuses usually live only three to five years. Near the end, a female finds a den and lays tens of thousands of eggs, hanging them in long strings from the ceiling.

Then she stays. For around six months, sometimes longer in colder water, she guards the eggs, blows fresh water over them, and keeps them clean. She does not leave to hunt, and she does not eat.

When the eggs finally hatch, the young drift out into the sea, and her life ends soon after. It is the pattern for her species, and it is part of why so many octopuses start at once: her whole life's effort goes into one generation. Each tiny hatchling that drifts away is already built like her, with three hearts and blue blood.

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Frequently Asked Questions

Why do octopuses have three hearts?

Two hearts pump blood through the gills to pick up oxygen, and the third pumps that oxygen-rich blood around the body.

Why is octopus blood blue?

Octopus blood carries oxygen with hemocyanin, a protein built around copper, which turns blue when it holds oxygen. Our blood uses iron-based hemoglobin, which is red.

How long do giant Pacific octopuses live?

Usually three to five years. A female guards her eggs for months without eating, and dies soon after they hatch.

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Sources

• Oceana: Giant Pacific octopus, three hearts, blue blood, color change and intelligence.
• Monterey Bay Aquarium: Giant Pacific octopus, size, range, hatchling size, and escape abilities.
• Wikipedia: Giant Pacific octopus, egg numbers, brooding period, and the female's death after hatching.
• Animal Diversity Web: Enteroctopus dofleini, lifespan of three to five years and reproduction.
• National Geographic: Giant Pacific octopus, habitat, size, and behavior.

Illustration: Octopus vulgaris by Comingio Merculiano, public domain, via Wikimedia Commons.

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