Why are coral colourful?

[Moort82]

There is probably an obvious reason i'm overlooking but why do corals have such an array of colours? I get why fish and inverts do but what does a coral gain from being brightly coloured? Its very different from a flower say which needs to attract pollenators, so whats the benefit for corals, i realise everything in evolution happens for a purpose.

 

[elegance coral]

The algae/zooxanthellae within coral utilize light of different wavelengths. The coral and its zooxanthellae can be damaged by wavelengths in the ultraviolet range. The coral can adjust the wavelength of light they are exposed to by reflecting some away. They use proteins, similar to GFP, to do this. It's this reflected light that we see when corals seem to glow. It works like sunscreen for corals.

 

[Sandberg1222]

We have a very creative creator

 

[Chris27]

I thought the color was there so someone could give it a ridiculous name and sell a 1/2" piece of it for $600.....are you telling me Mother Nature has another idea?

 

[Moort82]

The algae/zooxanthellae within coral utilize light of different wavelengths. The coral and its zooxanthellae can be damaged by wavelengths in the ultraviolet range. The coral can adjust the wavelength of light they are exposed to by reflecting some away. They use proteins, similar to GFP, to do this. It's this reflected light that we see when corals seem to glow. It works like sunscreen for corals.

That's tickled the synapses, i remember reading about that a while ago and its coming back. Makes complete sense but why the different colours? Evolution? you'd have thought that corals which exist in similar niches would have similar colouration unless their is another different key?

 

[jeff@zina.com]

The zooxanthellae are different species, in different quantities, for each coral and no coral is at the same depth so the wavelength reflected off them is always different.

Jeff

 

[Moort82]

Sounds simple when you put it like that

 

[chrisv]

I thought the color was there so someone could give it a ridiculous name and sell a 1/2" piece of it for $600.....are you telling me Mother Nature has another idea?

That's only for Zoanthus and Echinophyllia species...mother nature really wanted form to follow function in the SPS world...

 

[disc1]

Some of it has nothing to do with color. Corals make within themselves some very interesting biomolecules that serve a wide range of functions. Some of these just happen to be colored or impart some fluorescence. The evolutionary drive was to have the certain biomolecule, and the color is just a consequence.

 

[chrisv]

Some of it has nothing to do with color. Corals make within themselves some very interesting biomolecules that serve a wide range of functions. Some of these just happen to be colored or impart some fluorescence. The evolutionary drive was to have the certain biomolecule, and the color is just a consequence.

This is a very interesting idea. Do you know of any examples?

 

[jdegrasse]

+1 on disc1.

So it is my understanding that zooxanthellae are golden-brown and not colorful. The coral itself produces pigmentation. If the coral has a ton of light (e.g. shallow water), then it doesn't need a lot of zooxanthellae to produce energy, and the brillant color shows through. If the coral is in deeper water, then it needs more zooxanthellae to produce the same amount of energy and the coral looks more brown.

I think of it like plants. They are green because of chlorophyll. In the case of deciduous trees, the chlorophyll is reduced in autumn and the underlying pigments (which are always there) show through. There are also many pigments in plants that bring brilliant colors.

What I don't understand is the concept of bleaching. If the zooxanthellae are expelled or die, then why aren't the corals more colorful? There must be a coincidental decrease in pigmentation somehow.

 

[Moort82]

+1 on disc1.

So it is my understanding that zooxanthellae are golden-brown and not colorful. The coral itself produces pigmentation. If the coral has a ton of light (e.g. shallow water), then it doesn't need a lot of zooxanthellae to produce energy, and the brillant color shows through. If the coral is in deeper water, then it needs more zooxanthellae to produce the same amount of energy and the coral looks more brown.

I think of it like plants. They are green because of chlorophyll. In the case of deciduous trees, the chlorophyll is reduced in autumn and the underlying pigments (which are always there) show through. There are also many pigments in plants that bring brilliant colors.

What I don't understand is the concept of bleaching. If the zooxanthellae are expelled or die, then why aren't the corals more colorful? There must be a coincidental decrease in pigmentation somehow.

I'm glad i asked know as its very interesting. I have read all about zooxanthellae algae being brown which is why zeovit helps with the colours if you dose the right things.
Its also nice that its a combination of things that i kinda already knew linking together to make sense.

 

[jdegrasse]

Dana Riddle has an excellent multi-part series on Coral Coloration. A good read if you want to know more.

Now, as for what they gain... I keep hearing the bio-sunscreen hypothesis quite a bit. It makes sense because UV is quite damaging to all living things -- it messes with the DNA and causes either cell death or unchecked cell growth (tumors). Virtually everything that is exposed to the sun has pigmentation. Albinism is a rare phenomenon. The pigments absorb dangerous wavelengths before it can damage the DNA.

Because pigments absorb a very narrow range of wavelengths, I can accept the idea that a collection of pigments are needed to catch the entire UV spectrum. The collection of pigments is what cause beautiful colors in plants and coral alike. Although coral beat the crap out of the plant world, IMHO. The actual diversity of pigments is a product of evolution.

 

[disc1]

This is a very interesting idea. Do you know of any examples?

I don't know any specific coral examples off the top of the head, but I can give a terrestrial example that explains what I mean.

A carrot contains a compound called beta-carotene. It's really good for you because your body uses it to make vitamin A. For the carrot, it's purely nutritional. But it also just happens to have a bright orange color. The color means nothing evolutionary to the carrot, because that part is normally underground. But the carotene molecule is an essential part of it's metabolism.

 

[BL1]

+1 on disc1.

So it is my understanding that zooxanthellae are golden-brown and not colorful. The coral itself produces pigmentation. If the coral has a ton of light (e.g. shallow water), then it doesn't need a lot of zooxanthellae to produce energy, and the brillant color shows through. If the coral is in deeper water, then it needs more zooxanthellae to produce the same amount of energy and the coral looks more brown.

If that were true, then deep water zoas wound be brown and yellow looking but, deep water ones are some of the most colorful ones IMO.

 

[jdegrasse]

If that were true, then deep water zoas wound be brown and yellow looking but, deep water ones are some of the most colorful ones IMO.

That's true, but they also do not rely on photosynthesis for their energy.

 

[MagicReefer]

Chlorophylls are abundant photopigments and, along with accessory or antennae pigments, harvest light energy. By-products of molecular oxygen and organic carbon are ultimately produced through the process known as photosynthesis.

If a form of chlorophyll - chlorophyll a - is exposed to strong light, it will absorb a portion of the light's energy and use it in photosynthesis. Chlorophyll a will also absorb and emit some of this light's energy at a lower energy level in a phenomenon known as fluorescence.

This is why corals are so colorful and even more-so under artificial lighting.

 

[jdegrasse]

That's not quite true, MagicReefer. Chlorophyl a absorbs light within the violet, blue (higher energy) and red (lower energy) wavelengths while mainly reflecting green -- that's the predominant affect.

Chlorophyll can fluoresce if you hit it with UV or high energy lasers, but that is not the source of the colorations. Leaves are normally green in sunlight.

The colors come from pigments within the coral that reflect the brilliant colors that you see under white light.

Often these pigments will absorb the blue light of "moonlights" and fluoresce which is why some coral have green to red colors under blue lights.

 

[MagicReefer]

When we stock a tank full of beautiful corals and supply them with the right lighting, the tank will glow like a 60's blacklight poster. I was assuming this was the base of the question, "why are corals so colorful?".

In general, it is the flouresence that most love and strive for in a reef tank. As to why this is, only God knows the real answer. I was refering to the how.

I am not sure about which part you think is not true....but to respond in kind....

Flourescent emissions (not reflections) of - clorophyll a - are generally considered red (not green) and are known to range from 660nm to 760nm.

On another note.....

Plants, marine algae and corals with healthy symbiotic dinoflagellates will flouresce when exposed to relatively high amounts of visible light. Chlorophyll flourescence is proportional (to a point) to the amount of photosynthetically active radiation (PAR).

 

[m2434]

Is the question about coloration or pigmentation?

Coloration comes from two prime components, the zooxanthellae, which is golden-brown and the pigmentation of the coral itself. Anything that decreases zooxanthellae density, or the density of chlorophyll within the zoox will reveal corals pigments more. Anything that increases the zoox or chlorophyll will darken the coral a bit, but too much will make it appear brown.

As for pigmentation, there are a lot of reasons that have been hypothesized. Most have to do with photo-protection, or internal reflection. However, there are probably a lot of reasons. Not much is actually known though, and there is a ton of debate.

One, really cool, newer idea that has come up is protection against oxidative stress from autotrophy.

Biochimica et Biophysica Acta (BBA) - General Subjects
Volume 1760, Issue 11, November 2006, Pages 1690-1695

Quenching of superoxide radicals by green fluorescent protein
Fadi Bou-Abdallaha, 1, N. Dennis Chasteena, 1, and Michael P. Lesserb,

aDepartment of Chemistry, University of New Hampshire, Durham, NH 03824, USA
bDepartment of Zoology and Center for Marine Biology, University of New Hampshire, Durham, NH 03824, USA
Received 7 June 2006;
revised 18 August 2006;
accepted 21 August 2006.
Available online 25 August 2006.

Abstract
Green fluorescent proteins (GFP) are widely used in vivo molecular markers. These proteins are particularly resistant, and maintain function, under a variety of cellular conditions such as pH extremes and elevated temperatures. Green fluorescent proteins are also abundant in several groups of marine invertebrates including reef-forming corals. While molecular oxygen is required for the post-translational maturation of the protein, mature GFPs are found in corals where hyperoxia and reactive oxygen species (ROS) occur due to the photosynthetic activity of algal symbionts. In vitro spin trapping electron paramagnetic resonance and spectrophotometric assays of superoxide dismutase (SOD)-like enzyme activity show that wild type GFP from the hydromedusa, Aequorea victoria, quenches superoxide radicals (O2 −) and exhibits SOD-like activity by competing with cytochrome c for reaction with O2 −. When exposed to high amounts of O2 − the SOD-like activity and protein structure of GFP are altered without significant changes to the fluorescent properties of the protein. Because of the distribution of fluorescent proteins in both the epithelial and gastrodermal cells of reef-forming corals we propose that GFP, and possibly other fluorescent proteins, can provide supplementary antioxidant protection.