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Aquarium.Net April 97

Eric Borneman writes on Seriatopora, Aquarium Net has numerous articles written by the leading authors for the advanced aquarist

Bird's Nest Coral..Feathers Not Included

and coloration, part 2

By Eric Borneman

(Brush, Needle, Pink Nest, Bush)

Subclass: Zooantheria Order: Scleractinia Family: Pocilloporidae Genus:Seriatopora species: hystrix, caliendrum, subulata, aculeata and others

I love Seriatopora! In fact, I think it is my favorite coral. For years, I drooled over pictures of this beautiful lacy creation with its sharp needle-like branches. It was so elegant, so fragile, and to me represented all the aspects of SPS corals, Highly branched, tiny polyps, rapid growth, and impossible to keep! Five years ago, Seriatopora was available only very occasionally from a few dealers. At the time, all were wild caught and the general rule was that if it had thin branches, it was very hard to keep, even for a small polyped fact, so daunted was I that I never gained enough courage to own one until about a year ago. Glad I did, too! Allow me to continue....

Although the genus is composed of perhaps five recognized species, many more subspecies are found around the Indo-Pacific, reaching the entirety of the east African coast with at least one true species being found in the West Indies. Seriatopora hystrix is the species that almost all hobbyists will find as available to the hobby, as it is very common in shallow reefs. The individual colonies do not grow so large as the more imposing Acroporid colonies, but usually form small lacy nests of prickly points about the size of a football or slightly larger. As if the distinct colony formation and extremely thin branches are not enough to recognize this species, the corallites of Seriatopora are arranged in nice neat rows along the branches, and the polyps extend out very little. In nature, the polyps extend at night, but I have found that, like most corals in the aquarium, they more frequently extend during the day, and possible at night as well. The branches are extremely sharp and can even puncture the skin if mishandled. Fusion of branches is extremely common, and there is a species of crab that actually imprisons itself in the branches by manipulating the coral's growth pattern while she waits for a small mate to crawl through the branches to her. Pink and brown are the most common colors for this coral, often with highlights of green and pink. More rarely, a yellow morph, generally from deeper water, may be seen as an available specimen.

Aquarium care for Seriatopora is much the same as for other SPS corals. Water quality should be excellent. It is found that many wild caught specimens do not seem to fare well in captivity, with the pink morph being more difficult to provide proper conditions to ensure its success. However, the rapid growth and easy fragmentation of this coral has allowed it to be fairly accessible as a captive bred specimen. Thanks to Noel Curry of Scientific Corals, who provided my specimen, I can happily report on the care of this coral. I purchased a small fragment with about 8 branched tips that had attached to a small heavy, 11 months later, there have been uncountable branches that have fused, and approximately 200 branch tips are showing...this coral has grown compactly, but very quickly, and is approximately twenty times greater in mass and four times larger in diameter than it was when I received it. The most amazing thing I have found is its tremendous tolerance of light and current. Although it prefers strong light (especially to maintain color) and water movement, it seems to grow well in virtually all areas of several different tanks. While most reports of wild caught Seriatopora stress the fragility of this coral, I have found it very easy to keep. It is easily fragmented to produce new colonies. Seriatopora is also well known for another method of reproduction common in its relative, Pocillopora; polyp bail out occurs when the coral reacts (usually to a stressful condition) by ejecting its polyps which can then settle and attach to substrate. Each polyp can then begin calcifying and secrete a new skeleton.

An interesting aspect of this coral is its coloration. Like related Pocillopora, it can contain the pink pigment, Pocilloporin. With this introduction, the subject of coloration brought up in last months article can begin anew. Last month, I covered the vast array of different pigments that are contained within the tissues of corals, especially those found in highly light adapted species. This month, I would like to focus on aspects of the findings involved with these pigments, and how they can possibly be maintained in our aquariums.

As Dr. Terry Siegel wrote in the most recent edition of Aquarium Frontiers magazine, how a few years ago, small polyped stony corals were more or less a rarity that few people could find, much less be capable of maintaining with long term success in their reef tanks. Times have changed rapidly, though, and the proliferation of these corals has become an obsession for many reefkeepers. Along with their long term success, have been great strides in making mini-propagationists out of home aquarium enthusiasts, as well as great advances in the maintenance of their often bright colors. Several years ago, most reef owners found that even under the best conditions, most colored SPS corals would turn brown in a fairly short period of time. While the colony may have continued to thrive and grow rapidly, the loss of coloration was a bit of a sore spot. It was soon discovered that the intensity of the lighting was sorely lacking in most tanks, as these corals could often tolerate lighting on the order of 10 or more watts per gallon. Coupled with this was the increasing availability of metal halide lamps with high color temperatures of 10000K and 20000K. These bulbs are a paradox, though, since these bulbs simulate the color of deeper water. Yet, the effect they had was similar to the more shallow environment in terms of maintaining and producing the bright colors found in shallow reef corals. It has been speculated that the higher incidence of near UV light produced by these bulbs was more important to the maintenance of color than the actual bulb temperature. To be sure, some hobbyists experimented with potentially damaging UV bulbs and found enhanced coloration of SPS type corals. So, with buzzwords like PAR, lumens, color temperature, wattage and others being flung around with incredible abandon among the technologically and scientifically driven hobbyists, I feel a few major points have been overlooked. Namely, that of the function and natural occurrence of the pigments.

The beginnings of success in maintaining coloration of corals through the use of high intensity and spectral temperatures deserves some pondering. First, it must be assumed that it is impossible, or nearly impossible, for most people to duplicate the conditions of the sun artificially in our home aquaria, in either total spectrum or intensity. From a photosynthetic point of view, this has some interesting connotations. First, the vast array of pigments found within the photosynthetic apparatus certainly have the capacity to produce a rainbow of colors. Indeed, through the selective oxidation and accumulation of certain pigments in a favorable response to given conditions could and does allow for numerous color variations.

However, the predominant response of corals to incresed light intensity is an increase in the amount of zooxanthellae in the coral cells to maximize the photosynthetic opportunity, and to increase growth and reproductive chances. When corals are subjected to lower than normal light levels, they adapt by increasing the amount of pigment in the zooxanthellae and by increasing the size of the photosynthetic units within the cell. This response is logical to maximize the limiting amount of light available to shade adapted or deeper water corals. In both cases, the result of the zooxanthellic changes is a perceivable darkening of the coral. By darkening, I mean that the coral becomes a darker brownish color. In fact, increased light does not tend to produce bright and colorful hues in the natural environment, at least in terms of the common photosynthetic pigments, despite their common occurrence in such environments.

Taking findings of natural condition to the captive level, we can say that even under the best of circumstances, the light in the home aquarium is substantially less than that on the reefs. Thus we should imagine that the corals would darken from their natural color as the amount of pigment and the size of the photosynthetic units increase. Indeed, darkening does occur, but in a contrary way. When most corals are treated to an upgraded lighting system in terms of the amount of PAR light being offered, they tend to darken as would a coral moved to a more intense area of the reef. In other words, they respond as if the darkening had occurred from the result of an increase in the number of zooxanthellae. This seems illogical, since in almost all cases, the light above the tank will be substantially less than that present on the reef, and the initial darkening should be like that seen in shade adapted corals. The increased lighting logically should bring about, if anything, a return to non-shade adapated coloration.

Taken on another level, most brightly colored SPS corals are found in areas of high light intensity. Perhaps the maximally darkened zooxanthellae are overpowered by another type of pigment that either occurs overwhelmingly apparent over the pigments of the dinoflagellates, and may be either directly or indirectly involved or uninvolved in photosynthesis. Another possibility is that the coloring pigment is one that is more superficial in the actual tissue and effectively masks the typical brown color of the underlying algae. Yet another possibility is that the perceived color is an illsuion of sorts. Unfortunately, the other pigments that are known to exist do not fit this qualification. Since these corals are found in such bright light, perhaps the pigment acts as a protectant from harmful radiation of provides some sort of other adaptive function. Yet, the principle UV protecting substances found in shallow water corals are clear and have no color at all. It is known that the more brightly colored corals seem to have this adaptation at a metabolic cost. The corals are less able to adapt to changing light conditions, are more prone to rapid tissue necrosis, and have a decreased growth rate compared to their more subtley colored relatives.

What could be so important in terms of function that the coral would choose to adopt a bright color that does not seem to provide UV protection and does not seem to have any photosynthetic function, except to perhaps hinder maximal photosynthesic rates?

A final anomaly is that often only the tips of corals contain the bright colors. The tips of SPS corals contain the least amount of zooxanthellae, yet (surprisingly) are the most rapid growing area of the coral. So, logically, it would seem in this case that the coloration provides some means to enhance growth at the coral tips where the zooxanthellae were less likely to be able to provide maximum opportunity for growth. However, this combinations still seems less effective than if the corals were darkened with maximal amounts of zooxanthellae in the presence of the clear MAA's. This would seem like the most logical adaption based on research findings for maximal growth and reproduction ability.

It has been noted that increasing the intensity of lighting over a closed system has a duel effect. In some cases, symbiotic invertebrates with a certain specific shade of color will become more brown as their zooxanthellae respond to an increased photosynthetic capability. A few examples of animals which have this reacton are yellow polyps (Parazoanthus gracilis), Button coral (Cynarina lacrymalis) and certain anemones (Entamacea quadricolor). Other corals, and most notably the shallow water SPS corals, may actually have the reverse effect when exposed to increased intensity. Examples of this behavior occur in species of Staghorn (Acropora sp.), Velvet (Montipora sp.), and Bird's Nest (Seriatopora sp.). Still others, like Horn corals (Hydnophora sp.) andElegance corals (Catalaphyllia sp.) often show no change at all in terms of color resulting from increased light intensity. Still, many corals and invertebrates seem to have the ability to exchange one species of zooxanthellae for another as a response to a change in lighting intensity, and it may even cause a noticable change in perceived color. However, the change is usually seen as a substitution of brown or green shades as the symbiotic algae do not seem to occur in what one would consider to be "bright colors" such as red, blue, and purple. Thus, it would seem as though the intensity of light is not directly attributable to color change, but may be an indirect result if it occurs at all.

Similarly, the color temperature of bulbs has been implicated in maintaining and promoting bright coloration of captive corals. Since the spread of the specialized high temperature 10000K and 20000K bulbs, most hobbyists have noticed increased coloration in their corals, notably SPS corals. There are problems with this finding as well. First of all, the continuation of certain symbiotic animals to noticeably darken in response to these bulbs still exists. In other words, not all animals respond by becoming "brighter" or more colorful. Second, as mentioned, these bulbs simulate the spectrum of a deeper water environment by containing a higher proportion of blue in their spectrums. As mentioned in Delbeek and Sprung, Nillsen and Vossa, Riddle, and in meteorologic data, the spectrum of sunlight found on the reefs where the most brightly colored corals are found most nearly approximates the color temperature of the 6500K bulbs. Yet these bulbs are not as well known for causing coloration of corals. Some prominent hobbyists have noted that a combination of spectrums seems most effective, while others have advocated small amounts of potentially tissue damaging UV light in excess of the incidental UV light emitted by fluorescent and high intesity metal halide bulbs. Thus, it would seem that despite a preponderance of evidence supporting the ability of high temperature HQI bulbs to enhance coloration, there seems to be no logical explanation behind this least not at present...except in the implication of UV light. Unfortunately research has not lent credence to this school of thought yet, either.

Regarding the change from natural sun conditions when corals are collected through the interim before the corals are exposed to their final lighting conditions in the captive conditions, there are some more discrepancies. Time seems to play a discordant role. While certainly some corals may have a fairly lengthy amount of time spent out of their natural environment before being placed in a "new home,", others spend considerably less time out of sunlight. In fact, many corals spend less than 48 hours out of sunlight before being introduced to aquarium lighting. Yet, photoadaptation is usually neccesary with most species to avoid light shock and potential bleaching of zooxanthellae. Why is this? There are certainly many periods of time in nature when storms are present, and corals must often go at least this long without experiencing full intensity sunlight. When storms pass in the tropics, they can do so very quickly, and light and UV intensities increase almost instantaneously to a degree far greater than anything we can muster using even our most powerful metal halide bulbs. In fact, sunlight often appears from behind cloud cover faster than the warm up time of our bulbs. Yet, bleaching does not occur in nature under these conditions, and the often needed gradual acclimation of corals in the aquarium would seem unwarranted. Yet, experience proves that it is not, as bleaching can occur very rapidly when a new specimen is put under intense lighting. It would seem that the sooner collected specimens could be exposed to intense light after their transit time, the greater the chance for their complete and rapid adaptation to the aquarium. Furthermore, it would appear that whatever natural chemicals are manufactured by the coral to allow for this flexible and remarkable photoadaptive behavior are either not expressed after collection or under artificial light, are somehow rapidly degraded during or immediately after the collection of the specimen, or the collectors and dealers in the shipping and sale of these corals are continually deceptive...and to a degree far greater than expected! Unfortunately, there are many documented cases where actual transit time from collection to captive placement is on the order of twenty four hours (the equivalent of but a single cloudy day), and bleaching still occurred upon introduction to the tank lighting conditions. Thus I hypothesize that there is a yet another quantifiable component of light and its effect on coral metabolism that is being overlooked.

Although I have several more points I would like to cover, including my own theories based on observations and readings, I think this may well be enough be enough information to digest for one month. Next month, I will finish my series on coloration with some fascinating information that may hopefully open some eyes and result in some further elecidation of a cryptic topic. Thank you all for tolerating my long winded discussions.

Eric Borneman

Created by liquid
Last modified 2006-11-18 19:42