Final answer:
Octopi use camouflage to blend into their surroundings and ink release as a defense mechanism to escape from predators.
Step-by-step explanation:
The two defense mechanisms used by octopi are camouflage and ink release. Octopi can change their skin color and texture to blend into their surroundings and evade predators, an adaptation known as camouflage. In addition to this, they have an ink sac that enables them to release a cloud of ink. This ink cloud can serve as both a visual shield, allowing the octopus to hide or flee, and as a decoy to misdirect predators, providing an essential escape mechanism.