Red, green, and brown algae have accessory photosynthetic plastids containing different pigments than the chloroplasts.
It is known that chlorophyll absorbs red light and reflects green. That's why plants containing chlorophyll are green. At a depth of the sea where these algae live, there is no red light but different. Red, green, and brown algae have other pigments that can absorb that different light and which allow these algae to maximum use sunlight.
