- Hi guys and girls, I'm ReefMan, and today we're going
to learn about why corals have all the colors
that we enjoy in our reefs.
Corals actually get a large portion of their food from
their zooxanthellae, which are dinoflagellates
of the genus Symbiodinium (laughs).
And these symbionts require a specific amount of light
to actually thrive and do well.
It's thought that corals actually produce
the colorful proteins that we see
to protect that symbiotic algae from the strong light.
Under normal daylight, the dinoflagellates make up
most of the color leading to brownish or reddish coral.
There are two main groups of proteins
that are responsible for color in corals.
We have fluorescent proteins like green fluorescent protein,
yellow fluorescent protein, red fluorescent protein,
similar proteins with other colors all inventively named.
These are all the types of proteins that fluoresce
under actinic light, and they're primarily responsible
for colors like green, red, purple, blue,
anything that lights up under actinic light.
The other group of proteins
is something called a chromoprotein.
These don't light up.
They don't fluoresce like the fluorescent ones do,
but they're responsible for red, purple and blue.
A one that you might be familiar with is hemoglobin.
It's a chromoprotein that makes your blood red.
Fluorescent proteins absorb light, and then emit light
in a slightly different part of the spectrum.
It's called fluorescing.
Close to the surface, above about 20 feet,
there is a lot of light available,
and therefore a lot of different colors
are needed to absorb it.
Below about 20 feet where the light is mostly blue,
red and green colors dominate.
Colorful proteins in coral tissue work like a sunscreen
for the zooxanthellae, and they can reduce light
by up to 50% in some wavelengths,
or over the whole spectrum about 18%.
They absorb harmful wavelengths and then let others
pass through to the underlying tissue.
These proteins can make up a big percentage
of the overall soluble protein in a coral,
up to 14% in some tissues.
The tips of coral contain almost no zooxanthellae,
and so the color is different.
It's just proteins plus reflections
from the white skeleton inside.
The proteins in the tips help shield the coral
allowing zooxanthellae to colonize the areas to grow.
As light increases it activates genes in coral
that produce the colorful proteins.
Some corals activate more genes than others,
even in the same species or location,
which causes some corals to be more colorful than others
even if they're living right next door.
Corals get more colorful in brighter light
because the proteins act as a sort of sunscreen,
more light, more sunscreen you need.
Conversely, as heat goes up,
the production of the proteins goes down,
leading eventually to bleaching and coral death,
since it can no longer protect itself from the sunlight.
A single coral can have a multitude
of different colorful proteins.
For example, a single Acropora millepora
had three different cyan and green fluorescent proteins,
three different purple or blue chromoproteins,
and one red fluorescent protein, so it had multiple of them.
Why do deepwater corals also have fluorescent proteins?
They're protected by the sun just because they're so deep,
and no one actually knows why.
This is an active area of study.
Conversely, why do two corals of the same type
growing right next to each other look different?
And we think it's because of evolutionary protection.
By allowing individual corals
to express their genes slightly differently,
it protects the species from environmental change.
Because if something changes,
one might survive, the other might die.
It takes Acropora about six weeks
to acclimatize to changes in light,
because this process involves switching on and off genes,
and producing all these proteins,
and that's why it's important to start corals
lower in the tank rather than higher.
Lower light is less likely to do damage to tissues
that are not prepared
for the high light from your reef tank.
(synthesizer music)
I hope you enjoyed learning about fluorescent proteins
and all of the different ways
that our corals become colorful.
Happy holidays, and I will see you next week, bye.