Octopuses Have Three Hearts and Blue Blood: Ocean's Alien Creatures

Octopuses are among the strangest creatures in the ocean with three hearts pumping blue blood through their bodies. This bizarre cardiovascular system evolved to help these intelligent invertebrates survive in low oxygen marine environments. Two of the hearts, called branchial hearts, pump blood exclusively to the gills where it picks up oxygen. The third heart, called the systemic heart, pumps the freshly oxygenated blood throughout the rest of the body to power the octopus's organs and eight flexible arms.

Why Octopuses Need Three Hearts

The three heart system exists because octopus blood is far less efficient at carrying oxygen than human blood. Octopuses use hemocyanin to transport oxygen instead of hemoglobin. Hemocyanin contains copper rather than iron, which is why octopus blood appears blue instead of red. Copper based blood works less efficiently than iron based blood at binding and releasing oxygen molecules. To compensate for this inefficiency, octopuses evolved two extra hearts dedicated solely to pushing blood through their gills. The branchial hearts create extra pressure that forces blood through the fine capillaries in the gill tissue where oxygen exchange occurs.

The Swimming Problem

Octopuses face an unusual problem when they swim. The systemic heart that pumps blood to the body actually stops beating while the octopus swims using jet propulsion. Swimming exhausts octopuses quickly because their main heart shuts down during the activity, leaving them temporarily without circulation to vital organs. This is why octopuses prefer to crawl along the ocean floor using their arms rather than swim. Walking keeps all three hearts functioning normally. When octopuses do swim, they expel water from their mantle cavity in powerful jets, which is the same cavity that houses their main heart. The physical mechanics of jet propulsion apparently interfere with the systemic heart's ability to beat.

Blue Blood Chemistry

Hemocyanin gives octopuses several advantages despite being less efficient than hemoglobin. The copper based molecule works better in cold temperatures and low oxygen environments where many octopus species live. Hemocyanin remains dissolved directly in the blood plasma rather than being contained in blood cells like hemoglobin. This makes octopus blood thicker and more viscous than human blood. The blue color only appears when the hemocyanin is carrying oxygen. Deoxygenated octopus blood actually appears clear or pale. When octopuses are stressed or after vigorous activity, you can see their skin take on a bluer tint as oxygen rich blood flows near the surface.

Nine Brains Working Together

Beyond their three hearts, octopuses also have nine brains. The central brain is located between the eyes and coordinates overall behavior and processing. Each of the eight arms has its own mini brain called a ganglionic cluster that controls movement and processes sensory information independently. About two thirds of an octopus's 500 million neurons are located in these arm brains rather than the central brain. This distributed nervous system means each arm can taste, touch, and even make simple decisions without waiting for instructions from the central brain. A severed octopus arm can continue moving and reacting to stimuli for hours after separation.

Intelligence and Problem Solving

Octopuses demonstrate remarkable intelligence for invertebrates. They can solve complex puzzles, open jars, navigate mazes, and use tools. Octopuses recognize individual humans and show different behaviors toward people they like versus those they dislike. They can change color and texture in milliseconds to camouflage themselves or communicate emotions. Some species carry coconut shells or other objects to use as portable shelters. Octopuses in captivity have been observed escaping their tanks, traveling across lab floors to other tanks to eat fish, and then returning to their own tanks. This combination of curiosity, memory, and problem solving rivals some mammals.

Short but Intense Lives

Despite their intelligence and complex biology, most octopuses live very short lives. Depending on the species, octopuses typically live only one to five years. The giant Pacific octopus has the longest lifespan at about five years. Most smaller species live just one or two years. Octopuses die shortly after reproducing. Females stop eating after laying eggs and spend weeks or months guarding them until they hatch. The female dies soon after the eggs hatch. Males also die within a few months of mating. This reproductive strategy means octopuses cannot pass learned knowledge to offspring, yet they still develop sophisticated behaviors through individual learning during their brief lives.