Why can red algae live in deeper water than green algae?
Blue light penetrates deeper in water. The red algae can do photosynthesis in blue light.
Like all algae, red algae depend on photosynthesis to produce food. Most varieties of algae live near the surface of the water in order to get enough sunlight to live. Since they can absorb blue light, red algae can live in much deeper water where light of long wavelengths -- like red -- can't reach.