The chemical element that gives the blood of a lobster a bluish tint is copper. Lobsters, like many crustaceans, have a blue-colored protein in their blood called hemocyanin, which contains copper. This protein functions as an oxygen-carrying molecule, similar to the iron-containing hemoglobin found in the blood of mammals. However, unlike hemoglobin, which gives blood its red color, hemocyanin turns blue when it binds to oxygen.
Hemocyanin is found in the blood of many arthropods, mollusks, and some other invertebrates. It is a copper-based protein that binds to oxygen and transports it throughout the body. Hemocyanin is less efficient at oxygen transport than hemoglobin, but it has the advantage of functioning in a wider range of temperatures and pressures.
It is interesting to note that while the blue color of hemocyanin is more visible in the clear blood vessels of crustaceans and mollusks, it is not visible in the opaque blood vessels of cephalopods such as octopus and squid.