3 Algae
Classification by colour: green, brown and red
Ur rummatadur dre liv : glaz, du, ruz
Algae are classified by colour, which varies according to the quantity and type of pigments they contain. These different pigments allow them to adapt to changes in light.
All algae contain chlorophyll, the pigment needed for photosynthesis. Some also have accessory pigments that let them capture whatever light is available at the depth where they live:
- Green algae: chlorophyll a and chlorophyll b absorb red light.
- Brown algae: fucoxanthins absorb green and blue light.
- Red algae: phycobilins absorb green and blue-green light.
Why depth changes everything
Sunlight contains every colour, but it travels less well through water. With depth, some colours fade faster than others, depending on their wavelength.
Algae have adapted to these variations through their pigments, and they arrange themselves at different levels on the foreshore: the green ones near the surface, the brown ones lower down, and the red ones deeper still — as far as a hundred metres down.