Why are reefs so colourful?

[Large Polyp Dave]

I was reading the recent national geographic magazine, and there is an article that poses the question to the reader of why reef ecosystems have such diverse colours. I've read through it a couple of times, but they never seem to give a definitive answer...

Does anyone here know?

[aquaman67]

One reason the fish are so colorful is to defend territory.

Freshwater lakes and rivers aren't too deep so fish can go almost anywhere. Space isn't scarce, but food is. So freshwater fish are drab so they blend in and won't get eaten.

Even though reefs make up about 1 % of the ocean, 90 % of the fish live on reefs. Food is more blentiful but space or territory is scarce. So the fish can be more colorful and don't have to worry about standing out and getting eaten.

But they are territorial. Most marine fish don't school, even notice that?

There are many freshwater fish that school. The only freshwater fish that are really aggessive are african cichlids. And note they are colorful too.

[Kogo]

african chiclids (mbuna) also live on reefs of sorts in the rift lakes.

[Ochi]

Well for colors of corals it has to do with the pigment used to protect the coral from getting "sunburned", which is why the more powerful the MH (usually) the more intense the colors...

[Jabarten]

I have been under the impression, and the same is possibly true for animals in the other vast biologically diverse ecosystem otherwise known as the Tropical Rainforests, that intense coloration is to make similar animals stand out, and find each other, and be able to reproduce. Ie., hard to find another fish or frog, or whatever to reproduce, if they are all the same color!!...

Then again, that is just the impression I have been working under...Jason

[Ti]

african cichlids are pretty colorful.

[Moisted]

It should be mentioned that there are certain colors that are not even visible by human eyes. In other words many corals and fish that we know actually have different color signature in the ocean, which we cannot detect.

For example, there is a color called "Cleaner Blue", which the cleaner fish and crustaceans emit, it tells the other fish (possible clients) that cleaner service is available.

"Cleaner Blue has a long wavelength component (not visible to our eyes) and is therefore quite different to other blues known in other fish. These cleaners include fish species from a wide range of families both from the Pacific and the Caribbean as well as a Caribbean shrimp, strongly suggesting that this colour is connected in some way to their lifestyle..."

More research here ...

[Moisted]

The color of corals is because of the zooxanthellae in their tissue.
Zooxanthellae are one-celled, colorful algae that use the energy from sunlight to produce nutrients, which they share with the coral.

The reason corals are more colorful and healthier under strong light is because the zooxanthellae can produce more nutrients and in turn cause the coral to grow and reproduce.

[Ochi]

Yep I just checked...it is indeed the zooxanthallae that cause the colors

[astronaut]

Why are the fish of coral reefs so brightly colored? Which colors can they see? Are their bright colors camouflage to each other? Or are they saying “Don’t eat me!�? These are the questions many marine biologists are trying to answer. There are many theories, but none completely confirmed. Some theories are that… Fish can’t see the same range of colors as us, so a bright blue and bright yellow striped angel fish’s blues would disappear in the yellow of the corals, and while swimming in the open water, the yellows would be indistinguishable, like the spaces between letters on a page across the room… The colors mean things, like the bright colors of cleaner shrimp saying, “Pit Stop.�… Brightly colored fish are telling the other fish that they’re poisonous… Some fish mimic others known to be poisonous so that they won’t be eaten, like the Toby filefish mimics the saddled Toby puffer fish… Bright colors help fish keep track of who’s who. "It's a very good idea," says Marshall. People may not appreciate the difficulty of identifying species mates "because we're not living among a hundred other hominids." All over the world, marine biologists like N. Justin Marshall, Jill Zamzow, George Losey, and Gil Rosenthal have been working for years on answering these questions.

that was my summary for a current event report i had to do in school on this article (http://www.sciencenews.org/articles/20041106/bob8.asp)

hope that helps,
peter

[45commando]

I think the fish are so vividly colored for a few reasons.As stated above,so that same species can find each other.Secondly some of the bold patterns are to confuse or warn predators(such as false eye spots or spines on tangs etc).At depths,some of the colours that look so vivid to us may well almost blend in.At night,for example red becomes almost invisible,so it is a great colour for a nocturnal fish.Lastly most freshwater systems are somewhat merky,so why waste all that time on being colourful,if a same species fish can't see you more than a few feet away.Just my opinions.

[chrismunn]

doesnt bright colors in the animal kingdom warn predators of toxicity, er something like that?
uv protective flourecing pigments in corals exposed to heavy long term sunlight

[Large Polyp Dave]

but what about from an evolutionary standpoint?

it would seem that being so bright and colourful would be working against the survival of a species. I'm aware that the algae is what gives a coral it's colour. but i still don't understand why they are that colourful. I think its absolutely amazing.


I mean what in the cnidarian family alone, you could find animals with every single colour in the rainbow.


Heh... maybe someone should start a reeftank that has their corals laid out in the order of the the colour spectrum. =)

[firefish15]

Originally posted by Moisted
The color of corals is because of the zooxanthellae in their tissue.
Zooxanthellae are one-celled, colorful algae that use the energy from sunlight to produce nutrients, which they share with the coral.

The reason corals are more colorful and healthier under strong light is because the zooxanthellae can produce more nutrients and in turn cause the coral to grow and reproduce.

THe bright colors of corals is not due to the zooxanthellae.The color of zooxanthellae is brown. In corals living in high light the color comes from pigments in the coral's tissue which protects the coral and zoox from too much light. In lower light corals the pigments act as reflectors to better utilize the available light. There are other corals too that produce colors which are not related to light. I don't think anyone really knows why they are produced. But some corals which appear brighthy colored to our eyes may appear dark in their natural habitat. In deep waters where little red light reaches, corals which are red will appear black.
Here is a link to Eric Bourman's Coral Coloration FAQ where most of this information came from:
http://archive.reefcentral.com/forum...hreadid=234253

[Moisted]

hmm.... you seem to be right Firefish, the zoox are apparently golden to brown in color. According to Eric it's the colorful pigments in the corals that are the main source of color, of course they combine with the brown color of the zoox. I think there are still a lot of opinions and unproven theories around the subject.

Thanks for sharing Eric's thread though, fascinating read...

[Perureef]

I dont quite remember where i read it but i know that certain wavelengths of light cant penetrate as far as others. For example wavelengths of red do not go as far as others, thus fishes at that depth cannot detect the color red. Thus many creatures that live at this depth are colored red because it provides camoflage (since no one can see red). This would allow many species to be bright and colorful without necessarily being detected and killed

[Kogo]

why are the reefs so colorful.

because when god created an orderly universe he thaught some vivid coloration would be a nice touch.

thanks God.

[PeteUK]

COLOURFUL is a WORD that HUMANS use to describe different wavelengths of light. It is not necessarily something which has to have a reason to be, it is just how something appears to us. To answer any questions like this from an evolutionary point of view you have to ask how these attributes appear to predators, prey and the like in their own environment. What we see is a rough / bad approximation of what might actually be exposed to selection pressure in nature.

thanks evolution

[johnpoole]

one reason is that at depths, color does not standout as vivid. a bright red fish or coral would appear dark gray, blending in with surrounding fanna is protection. female birds are the color of branches, due to hiding from bigger birds. male birds that don't set on eggs need color to standout to females. dull males don't get to breed, bright females get eaten before the can reproduce. natural selection determines a lot of coloration.. and yes that's the way the good lord designed it.. if fire gobies were in fresh water against brown/green background, they would make bass happy.. against red coral, in 50 feet of water, they don't end up on the menu as often

[Perureef]

well what we have to understand is that different environments and species have different selective pressures. Here on land and in shallow freshwaters sunlight is bright and thus has a great influence over us animals. many animals have adapted dull colors to avoid detection. This is also compounded by multiple selective pressures. In many birds and freshwater fish, for example, sexual selection has an overwhelming influence over the direction the males take in order to guarantee that they obtain a mate. Thats why over several million years the males of these species have become very bright and colorful; their need to impress females supercedes their best interest, to remain dull and thus out of sight of predators.
In deeper waters, however, sunlight (in the case of visual selection) plays a different role. as I mentioned previously, certain wavelengths dont reach the greater depths, so many species over time have adapted to take on the colors that do the reach the depths so as to remain undetectable (if at a certain depth one cannot see red because red wavelengths do not reach that depth, then it would be advantageous to the fish to take on a red coloration so as to remain undetectable). Remember that many species of fish do not see colors as well as we or other animals do, and in the case of deep reef fishes, i image that sexual selection plays less of a role in exterior coloration than it does in other species.

Sorry for the long post

[Perureef]

second paragraph second sentence: i meant to say "that do NOT reach the depths so as to remain undetectable (if at a certain...........)
sorry for the error