Quote:
Originally posted by EricHugo
Corals are a symbiosis between animal polyps and one or several types of many species and strains of single celled protists (dinoflagellates) collectively called zooxanthellae.
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Oculina, Tubastrea, Astrangia. These have no Symbionts, are they not corals?
Zooxanthellae can vary in color from golden to dark brown. They multiply in response to a non-polyp abundance of nutrients, specifically nitrogen which is limited by their host. They can also photoacclimate by producing pigments that make them darker or lighter in response to lower or higher light levels, respectively. In general, low light and/or high nutrients will result in a coral becoming darker brown colored as the zooxanthellae multiply and/or photoacclimate.
Coral polyps (sans zooxanthellae) have their own set of animal pigments, too. There are non-light related pigments, such as those that form in the skeleton of Tubipora musica, Heliopora coerulea, and Pocilloporids. Also, there are the vividly bright colors of the skeletal sclerites in soft corals like Dendronephthya spp. and Scleronepthya spp. Colored skeletal elements are also formed in gorgonians, often in their axial rods.
Are you considering pocilloporin a non light related pigment or are you referring to the rusty brown color of eydouxi and other skeletons? Is there a name for this pigment?
Also, there are colored tissue pigments, such as those found in the tissues of many azooxanthellate corals, many which are not found on coral reefs. Examples are Tubastraea spp., Diodogorgia nodulifera, Swiftia, most Pacific sea fans, etc.
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