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Acclimating Photosynthetic Reef Invertebrates to Captive Lighting

By Anthony Calfo                 www.readingtrees.com

 pix by Bob Fenner

Before acclimating coral or other photosynthetic reef invertebrates to a new aquarium system, one might ask, "Where did this animal come from on the reef?" The lives of many animals could be saved or eased if this small bit of information were provided on import. While such information is not yet readily available from importers of wild animals, consumers can and should demand such information from domestic growers of cultured reef invertebrates. Although the volume of cultured invertebrates raised each year grows, the preponderance of livestock must still be imported for the trade in ornamental marine animals. And so, we know from a practical standpoint that many corals are collected near shore in relatively shallow water. But which shallow corals are found in brightly lit areas, and which are found under ledges or in the shadow of other species? Indeed, many other corals and reef invertebrates are still collected at depth deliberately, or incidentally in other activities (harvesting shells, sea cucumbers, food items, etc.). The possible variations of light intensity in the roughly sixty foot of water that most coral are collected from are staggering. Until such information on wild products of the sea is provided, aquarists much exercise caution and assume the lowest denominator when acclimating coral and reef invertebrates to new lighting. It is, in fact, much easier for a stressed reef invertebrate from bright light to adapt to temporarily attenuated light in captivity than to shock and recover under a more similarly bright, artificial illumination to their former niche on the reef. This fact is mitigated by days or weeks of dark transit and holding of reef invertebrates through the channels of importation.

Water depth in aquaria is an often-underestimated obstruction to the penetration of light into aquaria. As water depth increases, particularly beyond 20 inches of water depth, the penetration of most high output artificial lighting systems is significantly reduced. With standard output fluorescent light bulbs this it is even more dynamic (within 12"!). This is hard for a lot of aquarists to understand or accept when they think about how much money they have invested in their lighting system. Actually, it is easy to allow oneself a false sense of security when viewing light below the water surface that appears bright to the human eye without comparison. However, time spent on a tropical reef on a cloudy day will produce a newfound respect for the intensity of light in the tropics. Not to mention the fact that water temperature in some regions is above 80F at 75 feet thanks to intense light energy! The loss of light through water at depth is not the only concern with artificial lighting. The distance of lamps above the water is also critical. Metal halide lamps, for example, at 18" can deliver four times as much light intensity by cutting the distance of the bulb to the surface of the water in half (9"). This is a fine example of why a small investment in a good light meter can be so helpful toward the ultimate success of coral display and propagation. There is no guesswork involved regarding the placement of photosynthetic invertebrates when a light meter is used with known parameters of guidance. Studies on natural reefs exist with numerical assignments to light readings that can be interpolated for applications in the mariculture of live coral. And more conveniently, an intelligent consensus of known successes with comparable species in captivity is effective too. It becomes apparent quickly that the quality and intensity of light above aquaria is a highly variable dynamic that the captive symbionts are at the mercy of.

Animals from intensely lit areas of a reef that are not supplied with similar lighting in captivity may appear to change color as they shed unnecessary U.V. reflective pigments. At that point, such animals may appear to be darkening in color, often to a darker brown or golden color. The aquarist often associates this with a decline in health, although that is not necessarily the case. The color change may be attributable to an increase in the population of zooxanthellae algae, or simply the greater visibility of resident zooxanthellae now visible in the absence of the U.V. reflective pigments. Whether the change is intolerable or not depends on if the coral's fundamental needs are being met by the decreased illumination. Many corals can survive in captivity with less surface irradiance than the optimum levels received in the wild environment so long as the compensation point of photosynthesis is met. We call this photoadaptation. And even without it, supplemental feeding of the animal can be compensatory.

The nature of physical changes in coral from the point of wild collection to re-establishment in captivity is quite interesting. Some changes and behaviors are often mistaken for favorable responses when adapting to new conditions. For example, it is commonly mistaken that the sudden swell and polyp expansion of some corals in the short time of weeks/months (particularly the fleshy LPS corals like Caryophylliids…elegant, hammer, bubble coral, etc.) is an expression of good health and growth. It is quite possible, however, and actually more likely that such individuals are struggling to meet their compensation point for photosynthesis due to inferior lighting and are panning for light when they swell. Real growth is measured by calcification (skeletal growth is admittedly slow for many Caryophylliids in captivity without supplemental feeding) and not by mere tissue girth.

Some examples of Caryophyllids below: Elegant (Catalaphyllia jardinei), Hammer (Euphyllia ancora) and Bubble Coral (Plerogyra sinuosa)

This was an especially common occurrence with early reef keepers when standard output fluorescent bulbs were the only lights that many aquarists used over the much sought after and shallow water colored corals. To add insult to injury, modified "Berlin" systems were all the rage with bare bottomed aquaria (no DSB and its nutritive by-products) and little or no feeding to any fish or inverts in an effort to keep nitrates down. In modern situations with the popularity of bright metal halide and high output fluorescents, the problem still occurs with some coral as they begin their term of captivity under optimum lighting, but factors such as aging bulbs, deteriorating water clarity (yellowed, turbid), debris and salt creep on lenses, and other factors reduce the amount of light actually penetrating the water. In turn, corals stretch out each day to an impressive and maximum size, "panning" in an effort to capture the diminishing light, which could be mistaken for growth. Again, a darker color change may coincide with this phenomenon (as with brightly colored yellow or green coral turning brown). One of the possible explanations for this change is that the low light stimulates brown zooxanthellae to increase in population and individual size, which lends to the darker appearance. In other cases on the contrary, the over-extended tissue appears to be thinly colored or watery.

Regardless of the explanation, a swelling and attractively polyped out specimen may not be healthy but rather struggling, and it is important to know the history and likely needs of a coral from the reef for long term success. Regrettably, coral coloration alone is not a definitive blueprint for coral husbandry. Not all coloration in reef invertebrates is zooxanthellae; some color is due to properties (such as proteins) that act as protective sunscreen to reflect excess light. In other cases, however, the bright reflective colors observed in some corals from depth may serve to refract weak light within tissue of more weakly illuminated coral. The rigors of import for symbiotic invertebrates without food or light can be quite taxing. Corals from all depths of a reef may suffer from shock, especially on import, and expel pigmentation. In such cases, translucent color may be attractive to an aquarist but is often evidence of a stressed animal. It could mean that the specimen has expelled nearly all of its zooxanthellae and the remaining color(s) you see are orphaned pigments! This is usually the case with "yellow" corallimorphs, "white" sebae/malu anemones and the tragically attractive "light pink" or "yellow" Trachyphyllia brain corals. Such colors rarely exist if at all in such healthy specimens in the wild. In general, coral in good health usually have dense, rich color and healthy but not over-extended polyp activity.

Examples of "normal" (wild) colored Sebae (Heteractis crispa) Anemone in Fiji, a bleached out captive specimen and one that has been artificially dyed yellow. 

Another common stress to corals in captivity regarding lighting and pigmentation is the frequent movement between gradients of light (as in the random and experimental placement of a coral vertically within a display by an aquarist). Such movement can be very dangerous within short periods of time. If you really want to kill your newly imported or otherwise acquired species of coral, be sure to move it around three, four or even five times during the first week to get just the right position for display purpose! Healthy coral are placed securely the first time with consideration for their actual luminary requirements. Aesthetic concerns are secondary. Frequent movement is one of the worst possible things that can be done to newly imported animals. They have low energy reserves from an extended period of time in transit without feeding (from photosynthesis and otherwise). Some species, by nature, need to feed almost constantly as evidenced by the minimal levels of fats/lipids in their tissue. Combined with the unavoidably inferior water quality in transit and change in light, stresses placed on imported animals are high. Many corals, after considerable periods of darkness in shipping, are exposed to three or more different lighting schemes in holding facilities along the path of custody before finally reaching a consumer's tank. A lot of energy is required by an animal and its' hosted zooxanthellae to make adaptive changes in pigmentation for survival.

Since the destination lighting is already very different from native illumination that the coral had grown under on the reef, a considerable effort is going to be made by every coral to survive under a new lighting scheme. Frequent vertical movement of a coral at any age in captivity is irresponsible and deleterious. If necessary, best results will be observed with lateral moves within a given display and moves between systems (as in the shipping of cultured specimens) with the help of a light meter. Aquarists are already challenged without industry policy or legislative recourse to persuade remote collectors to provide lighting information on imported animals. Domestic coral farmers, however, can do their customers and the industry a great service by trading animals with lighting information for each specimen. For coral farmers, a reasonably good light meter can be obtained for sometimes well under two hundred dollars to provide luminary history to customers and is a very small investment, not to mention responsible posture, in the business of coral propagation.


Acclimating Corals and Reef Invertebrates

to New Lighting Schemes


*Tips for Shipped, New or Otherwise Stressed Reef Invertebrates

Acclimation Tip: in summary of this section on acclimating coral, it is my recommendation that all newly imported coral, and coral from previously unknown levels of light, be placed in systems at a depth no less than 20" under higher output fluorescents and metal halide lamps (assuming the intensity of such light is appropriate after the animal overcomes stresses). Acclimation to the final level of display can be approached gradually in increments of 4-6" weekly or less often depending on coral behavior. Dedicated aquarists may wish to build or buy simple, weighted building blocks (like cubes made of acrylic) that can be used temporarily in an open space of the aquarium. Small blocks or shelves will help to acclimate a coral without concern in a well-stocked display for finding space along the rockscape incrementally in a path to the final position. Another interesting technique is to place a stack of coarse plastic window screen pieces above the new coral to filter light (perhaps on the aquarium cover) if a coral is to be placed immediately in its final position. Enough sheets for each day of the two to three week acclimation period will sit above the new animal. One sheet of screen is removed each day until all are gone, providing a gradual and filtered period of adjustment for the new coral. One can imagine many other ingenious ways of attenuating light during the critical acclimation period of a new reef invertebrate. Raising the light canopy for a new coral is not recommended with other established coral in residence. Indeed, after an extraordinary trip from a coral farm or wild reef to take up residence in a beautiful display, light shock should not be an issue to the empathetic and well-informed reef aquarist.

Excerpted and Revised from the chapter, "Corals Adjusting to Changes in Light" in the
Book of Coral Propagation, Volume 1
by Anthony Calfo


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