Red algae contain a pigment called phycoerythrin, which absorbs blue light and reflects red light. The reflecting of red light gives these seaweeds their appearance. It is thought, according to an article on American Scientific, that the record held for the deepest living seaweed is 268 meters below sea level!

Each Seaweed can be classified into one of three groups: Red, Green and Brown. The groups vary from one another in their own ways. Why certain seaweeds have their specific colour though is due to the pigment abundance and distribution found in each seaweed.

The two main Pigments that make up red seaweeds are Phycoerythrin (Red) & Phycocyanin (Blue). These two pigments allow red seaweeds to take on a wide ranging colour spectrum from deep red to bright blue.

Phycoerythrin (Red) is used as a natural dye in food and cosmetics. It has also been extensively explored and tested in the formulation of foods with “special effects”, such as visually appealing cake decorations, soft drinks, and alcoholic beverages (1).

Phycocyanin (Blue) on the other hand is most frequently used as a natural blue pigment in the food industry, to colour products such as jelly and bubble gum. It seems to be an even more attractive form of colouring due to its health promoting aspects (2).

One interesting fact to end on is how red seaweed have developed a cunning technique to make light harvesting more efficient. Red seaweeds assemble what are called phycobilissomes (PBS), whose job it is to capture solar energy and transport it to photosystems within the seaweed (3). They are like light absorbing antennae.