These findings were published Thursday in the journal Current Biology. The colorful protective layer is made up of pigments similar to green fluorescent protein — a substance found in some jellyfish, which glows when exposed to light.
It works in what's called an optical feedback loop. So while the color of coral typically exists because algae live inside the coral's cells, in this case, the coral itself makes the glowing pigment. That ability comes down to interaction with sunlight. The optical feedback loop explained — In healthy corals, the algae's photosynthesis process absorbs most of the sunlight that hits the reef. Without algae, though, that light is free to bounce around inside the coral instead — the excess light is reflected by the white coral skeleton.
All that action is stressful for algae and can dissuade the aquatic plants from returning to the reef. Unfortunately, email to the primary investigator requesting clarification has gone unanswered. Trend lines show that Pigments and decrease in fluorescent intensity as PAR increases, while Pigments and increase in intensity. Is this a case of photoconversion, where light intensity alters the chemical makeup of pigments and causes them to shift from one fluorescent color to another? It is common knowledge that corals often contain at more than one fluorescent pigment a Favia specimen was found to have at least one dozen.
Figure 18 demonstrates the possible but hypothetical increase or decrease in pigments according to light intensity alone. Imagine the possibilities we might observe when we add the effects of spectral quality on pigment expression. The exercise becomes mind boggling, and this is a relatively simple example!
There are only a few described cases of photoconversion in cyan pigments. Two are from Clade A nm to an undetermined wavelength in Condylactis gigantea — Labas et al. See Figures for additional information. Light mostly likely blue light induces a shift in fluorescence from blue-green nm to green with a peak emission at nm. After Papina et al. Light intensity and its spectral characteristics play important parts in promotion of coral coloration.
Certainly, these are not the only requirements and become deciding factors only when other conditions such as water motion and water chemistry are correct.
Surprisingly, these categories were fairly close to those seen in aquaria when I divided the number of light measurements made in aquaria and divided the total number into 4 categories containing an equal number see Figure These were my classifications:. A pigment from Clade A, the spectral signature suggests photoconversion is possible. After Labas et al. Hence, some sort of light-measuring device, whether a lux meter or quantum meter, would be most helpful in determining proper placement of corals containing cyan fluorescent pigments.
See here for comments on lux-to-PAR conversions: www. The double-peaked emission and excitation, for that matter suggests we are observing a pigment in transmission from one peak emission to another nm to nm, which is blue-green to green, respectively.
From Wiedenmann, When we examine the effects of spectral quality on pigmentation, we find in all cases that blue light promoted the expression of fluorescent pigmentation most effectively. Green light ran second best in promoting fluorescent pigment production, although the filter used by these researchers transmitted a fair amount of blue light.
The red filter effectively, and almost exclusively, transmitted red wavelengths and was least effective in coaxing the coral animal to produce fluorescent pigments. Lamp spectral quality is another issue that should be investigated further. Simple visual observations of corals within our aquaria support the experimental evidence that blue-green pigments are not all that difficult for corals to produce with these artificial environments.
In this article, we see that red light apparently fails to promote coral coloration as efficiently as either green or blue bandwidths. We discussed the effects of red light on coral growth in the December edition of Advanced Aquarist.
See here for details: www. The concept and practice of classifying pigments by clade is another important step. Previously, our best method of categorizing pigments was by fluorescence excitation and, more particularly, emission. While we can not say that pigments within a certain clade will react in roughly the same manner as another pigment within the same clade, we can begin to form generalizations.
With time, the clade categories will probably prove to be an important tool in our understanding of fluorescent pigments and their production and maintenance. If you would like to receive interesting content like this in your email Inbox, subscribe to our newsletter. In addition to our monthly newsletter , we will send you our weekly e-Bulletin with one fascinating topic, like today's article above.
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In shallow waters the pink, purple and blue coral colours are most striking. Beyond depths of around seven metres these colours tend to become dull since their brilliance depends on the reflection of red light.
Down there, where blue light dominates, the green and red fluorescence of some corals makes them stand out from the bluish-grey background.
Fluorescence can be best observed with the help of blue light torches and special filter masks under low light conditions. Using this equipment, the glowing corals make a night dive a psychedelic adventure.
Some corals increase the production of colourful protein pigments when they are exposed to more intense sunlight. Humans get a sun tan — corals become more colourful. We found the pink and purple proteins act as sunscreens for the corals by removing substantial light components that might otherwise become harmful to the algae hosted in their tissue.
Corals rely on these light-dependent miniature plants, the so-called zooxanthellae , since they provide a substantial amount of food. We have also explained why some corals accumulate exceptionally high amounts of colourful pigments in growing areas such as branch tips or near wounds. These areas contain essentially no symbiotic algae, so much of the light is reflected by the white coral skeleton instead of being used by the algae.
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