Any of the red pigments that form one of the two major classes of the *phycobilins
. They are found in all red algae, and act as accessory pigments in photosynthesis. They absorb the dim blue-green light that reaches the lower levels of the ocean where the algae grow, and pass it onto chlorophyll so that it may be used in photosynthesis. The deeper in the sea an alga lives, the more phycoerythrin it contains in relation to chlorophyll.