seaweeds have had a more diverse evolution than the green and the
species cannot stand desiccation and dominate the inter-tidal rock pools.
Others tolerate desiccation, such as the purple laver which can often
be seen stretched out like a dry black film over mussle beds on
seaweeds such as Polysiphonia lanosa are epiphytes,
these are plants that grow on other plants for physical support.
In this case the epiphyte benefits from the host's buoyancy lifting
it closer to the sunlight.
The red colour of the seaweeds is due to the larger
amount of red
phycoblin pigments overriding the green pigment chlorophyll.
pigments that colour it red have a purpose,
enabling the seaweeds to photosynthesis
light from a specific part of the light
spectrum. Within the group of phycoblins
two pigments are of importance phycoerythrin
and phycocyanin. Phycoerythrin absorbs
green, yellow and red light while phycocyanin
absorbs blue, green and yellow light.
These parts of the spectrum are the
type of light that penetrates the deepest
in sea water. The red pigments absorb
the light but chlorophyll is still required
to process it. This method allows red
seaweed to survive in low light conditions
where green seaweeds could not.
light intensity has an affect on the
red pigments which is reflected in the
colour of the seaweeds. With high light
levels the pigment starts to break down,
the seaweeds becoming pink or even bleached
white. With low levels pigment production
is stepped up producing really red plants.