Octopuses are marine animals known for their intelligence, camouflage ability, and complex behaviors. They have evolved unique biological features that allow them to thrive in diverse ocean environments. Exploring their internal systems reveals surprising adaptations, including a distinctive characteristic of their circulatory fluid.
The Striking Color of Octopus Blood
Unlike many animals, octopus blood is not red; it is blue. This unique coloration is noticeable. The blood can appear pale, but its bluish hue becomes visible in sufficient quantity. This blue color is due to the molecules responsible for oxygen transport within their bodies.
The Science Behind the Color
The blue color of octopus blood comes from hemocyanin, a copper-containing protein that serves the same function as human hemoglobin: to bind and transport oxygen throughout the body. While human hemoglobin contains iron atoms that give blood its red color when oxygenated, hemocyanin in octopuses contains two copper atoms. When oxygen binds to these copper atoms, the hemocyanin molecule turns blue. Conversely, when deoxygenated, hemocyanin becomes colorless. This copper-based oxygen carrier is suspended in the hemolymph, unlike hemoglobin in vertebrates which is confined within blood cells.
How Octopus Blood Works
Hemocyanin’s ability to bind oxygen is effective in cold, low-oxygen environments where many octopus species reside. This copper-based protein allows octopuses to maintain a steady oxygen supply even when it is not readily available. The octopus circulatory system is also adapted to support this oxygen transport. Octopuses possess three hearts: two “branchial” hearts pump blood through the gills to pick up oxygen, and one “systemic” heart then circulates this oxygenated blood to the rest of the body. This multi-heart system helps compensate because hemocyanin is less efficient at binding oxygen than hemoglobin, requiring more robust circulation to meet metabolic demands.
Comparing Octopus Blood to Human Blood
The primary difference between octopus blood and human blood lies in their oxygen-carrying proteins and resulting colors. Human blood is red due to hemoglobin, an iron-based protein located within red blood cells. When iron in hemoglobin binds to oxygen, it gives blood its red color. In contrast, octopus blood is blue because it uses copper-based hemocyanin, which turns blue when oxygenated. This chemical distinction highlights the diverse evolutionary paths organisms have taken to solve oxygen transport.