The January 2003 issue of Limnology and Oceanography (48:1) has a special section, part 2, which contains papers that deal with light in shallow waters including ultraviolet, and how this can affect remote sensing. In addition there are several papers that deal with coral fluorescence that might be of interest to aquarists.
Fluorescence in corals is a very popular topic of debate in not only hobbyist circles but also in the scientific community. While hobbyists are more concerned with the colors of their corals and how best to make them more colorful (either via one or all of high light intensity, blue spectrum bulbs or ultraviolet light) the scientific community is more concerned with the role that these pigments play in coral physiology, and how this fluorescence could be used for remote sensing applications of coral reefs. Recent studies are now beginning to show that the commonly believed functions of these pigments are not holding up under scrutiny. The following two papers are indicative of the research being conducted.
Mazel, C.H., Lesser, M.P., Gorbunov, M.Y., Barry, T.M., Farrell, J.H., Wyman, K.D. and P.G. Falkowski. 2003. Green-fluorescent proteins in Caribbean corals. Limnology and Oceanography 48(1):402-411.
One of the first fluorescent proteins identified was the green fluorescent protein (GFP) in the hydromedusa Aequorea victoria. Subsequent studies have shown that a large number of Caribbean and Indo-Pacific corals have fluorescent pigments that are closely related to GFP. GFP in corals emits a spectrum that peaks at 500-518 nanometers resulting in a strong green color. It is generally felt that fluorescence can have one or both of the following two roles: 1) provides photoprotection under high-light levels and 2) enhances photosynthesis in low- light conditions by providing additional photons. This fluorescence can be seen under normal light conditions or in some cases only becomes visible when light with the appropriate wavelength is used. Using molecular and biophysical approaches this study attempted to ascertain the ecological role of this pigment in the photobiology of Caribbean corals.
Nineteen species of stony coral were examined using a variety of techniques. In all cases, GFP was found in varying amounts. It should be noted here that GFP is also found in Ricordea, Palythoa, Zoanthus and the anemones Condylactis gigantea and Phymanthus crucifer. However, GFP levels were found not to vary much with depth. In fact, there was no correlation at all between depth and GFP levels. Measurements of reflectance and of the excitation spectrum for chlorophyll fluorescence in GFP-containing corals over a wide range of depths and GFP fluorescence indicated no evidence of GFP photon absorption either to enhance or reduce photosynthetic activity. If GFP plays a role in photosynthesis by either adding or taking away protons, then one would expect to see a correlation with depth as one does with other protective compounds such mycrosporine-like amino acids (MAAs) that protect against ultraviolet light, but there does not appear to beone in the corals they examined ( Montastrea faveolata and M. caernosa ). Compared to other non-photochemical methods that corals have to reduce the effects of excess excitation energy, the authors concluded that the photoprotection afforded by GFP is negligible in Caribbean corals. Another pet theory of aquarists is that ultraviolet light is involved in the production of fluorescent pigments. In the case of GFP at least this is most likely not the role it plays. The authors could find no evidence of an excitation peak in the range of UV (200-400 nanometers), suggesting GFP plays no role in UV protection. The authors, however, are quick to point out that it is still possible that GFP may play a role in helping a coral deal with environmental stresses such as high light, UV or temperature levels by as yet, undiscovered mechanisms. There is preliminary evidence that GFP levels are inversely correlated with superoxide dismutase (SOD) protein levels in corals exposed tolight and temperature levels that produced superoxide radicals (SOD is involved in their reduction). It is tempting to speculate on the possible reasons for this inverse correlation.
Mazel, C. H. and E. Fuchs. 2003. Contribution of fluorescence to the spectral signature and perceived color of corals. Limnology and Oceanography 48(1):390-401.
I can remember diving in murky waters in Indonesia when at 90 feet I came upon a day-glow orange Fungia. I quickly snapped a picture but was disappointed to find that when I got my pictures back it looked green and not the bright orange I had seen. This paper helps to describe why this occurs. Most early studies on coral color focused on qualitative observations of the color and quantitative measurements of its spectral characteristics. It was noticed decades ago that in many cases the bright, natural colors were often augmented by or due mainly to fluorescent pigments found in the animal tissue, this was especially noticeable with corals that appear orange or red at depth when those colors are already absent in the downwelling light due to the filtering characteristics of the water.
Corals can be colorful even without fluorescent pigments. As has been stated before (Delbeek and Sprung, The Reef Aquarium vol. 1), corals are predominantly brown because the zooxanthellae they contain are brown due to the fact they absorb most other colors. Other colors can also be found in the host tissues and are the result of non-fluorescent pigments. What many people may not realize is that just because a coral contains fluorescent pigments, they may not be apparent to our eyes. For example a coral that appears brown to our eyes under natural ambient light may glow blue under ultraviolet or blue light. This can be explained by several factors such as the spectral distribution of the ambient light and the strength of the fluorescence. The authors used the same measurement techniques as the previous paper to measure coral reflectance and fluorescence and the modeling of downwelling spectral irradiance to explore the contribution of fluorescence to the spectral signatures ofcorals as a function of variations in depth, solar zenith angle and fluorescence efficiency.
Spectra from several pigments were used from both Caribbean (p486, p515 and p 575) and Indo-Pacific corals (p538 and p583), the number refers to the wavelength emission peak of the fluorescence produced. Four of the emission spectra produced strongly saturated colors while the fifth p486, was relatively unsaturated. Both p515 and p538 produced a bright green fluorescence while p575 and p583 produced orange to red. It is important to note here that the emission spectrums of all these pigments were independent of the excitation spectrum, the emission wavelengths are averages and there can be quite a bit of variation, and that the excitation spectrum can vary from specimen to specimen for any given pigment. In order from least to most efficient in fluorescence: 486 (3-5%), p575 (8-10%) and p515 (10-12%)
The degree of fluorescence observed varies due to the spectrum of the downwelling light, which varies with increasing depth, and the amount of reflectance of the coral tissue in general. Some of the fluorescent pigments turned out to be more noticeable than others and it became obvious that the mere presence of a fluorescent pigment was not a guarantee that the coral would exhibit fluorescence under ambient light conditions. It therefore became appropriate to divide the fluorescent response between those pigments that exhibited “overt fluorescence” for cases where the corals would fluoresce under ambient light, and for those that exhibited “covert fluorescence” only when illuminated with an appropriate light source in darkness. It should be pointed out here that this last form is still emitted under natural light but is simply overwhelmed by the reflected light of the coral and as such is not visible to the naked eye.
In general it could be concluded that fluorescent pigments that absorbed wavelengths that are transmitted well by water, have high fluorescent efficiency, emit fluorescent wavelengths that are only moderately attenuated by water, and emit at wavelengths to which the human eye is most sensitive are able to produce the most striking fluorescent effects for human eyes. This is especially true for p575 and p583 that emit in the orange range of the spectrum, one that is attenuated enough by water to reduce any competing influence from downwelling light and coral reflectance, but not strong enough to reduce the emitted light. These corals absorb heavily in the green range of the spectrum, which is still easily transmitted through water. The greenish pigment p515 is the most widespread in corals but it emits in a region of the spectrum that is not heavily attenuated by seawater so would argue that it would be overwhelmed by ambient light, however, the high efficiency of this pigment andthe sensitivity of the human eye to green combine to give a high level of visible fluorescence. In contrast to these pigments, the blue-green p486 is not readily observed in nature. This is due to several factors. First this portion of the spectrum is readily transmitted by water so the degree of coral reflectance is high. Combined with the low efficiency and % color saturation of p486, the reflectance is great enough to overwhelm the fluorescence emitted by p486 under natural ambient lighting conditions. As a result green and orange emissions are the ones most commonly seen by divers.
Finally the mere presence of fluorescent pigments or any color for that matter should not be used as a sign that these pigments have a function. There is certainly a reason for the color, but there may be some other function of the pigment, and the color is merely a neutral by-product. No one knows yet what the functions of these pigments are, they may merely be due to genetic differences. The authors identify several areas where further research may lead to some idea of the functions of coral pigments, in particular the fluorescent ones: ecological studies that examine the relationship between habitat and color morph distribution, controlled studies to determine what factors control the expression of color in corals (probably the area of most interest to aquarists!), analysis of coral emission spectra and its relationship to vision in fishes, and molecular studies of the fluorescent pigments to determine a relationship between structure and function (this will also help toascertain the elemental composition of these pigments which may provide clues as to what elements might be necessary to replenish in closed systems to help maintain or intensify these colors e.g. manganese for anti- oxidants as has been speculated by Julian Sprung) . The authors feel that once the function of pigments and how their expression is controlled, is understood, coral color may prove to a good indicator of environmental conditions on a reef.
For aquarists this paper helps to explain why corals may appear certain colors under certain lamps. Obviously those lamps in the blue end of the spectrum such as actinic 03s provide light of such a narrow spectrum that there is no light in their spectrum for fluorescence in the green, orange and red ranges of the spectrum to compete against and helps to explain why corals under these conditions exhibit the greatest fluorescence intensity. Also high Kelvin metal halide lamps have a larger portion of blue in their spectrum that further enhances the fluorescent effect of some pigments.” It might also be interesting to add a little green to some lamp combinations in order to stimulate those corals that might contain orange fluorescent pigments such as Scolymia and Cynarina.
What is still not clear is why corals develop more color under some lamps as opposed to other lamps? Several of us have observed that corals will change color when lights are changed from one spectrum type to another, or from one wattage to another. If coral pigments offer no protection against ultraviolet light or high intensity as these two papers seem to suggest, then is it that the pigments are merely a by-product of some other reaction that is being driven by light intensity or the presence of ultraviolet light? I think this is an area that aquarists should be working with scientists on … I think the results would be very useful to both fields!
And for me … I finally have my answer … when I saw that day-glow orange coral it was emitting fluorescence in a wavelength that had been greatly reduced by the intervening water above, but when I took the picture with my flash the added colors in the flash overwhelmed the orange fluorescence of the coral … so next time … no flash.
Simones, F., Riberio, F. and D.A. Jones. 2002. Feeding early stages of the fire shrimp, Lysmata debelius (Caridea, Hippolytidae). Aquaculture International 10(5):349-360.
One of the problems encountered when attempting to rear ornamental shrimp is high mortality during the early stages of development. In this paper the authors assert that the reason for this high mortality is the belief that larvae do not need feeding until their egg yolk is completely consumed after 24 hours. In experiments with the commercial rearing of the marine ornamental shrimp Lysmata debelius they should that high larval mortality during early stages of larval collection could be reduced if they were fed immediately after hatching and not waiting 24 hours. Their work demonstrated that captive newly hatched L. debelius larvae ingest microalgae within minutes after hatching. When fed solely with Artemia nauplii, they had acceptable survival rates with stocking densities at or below 50 larval per liter; but when nauplii are combined with microalgae, survival was further improved to zoea stage 2 as initial mortality was reduced, and higher stockingdensities were supported (up to 75 larvae per liter). The microalgae used were Rhinomonas reticulata, Skeletonema costata and Tetraselmis chuii. Higher survival through metamorphosis to zoea 2 was always observed for groups fed combinations of microalgae including Tetraselmis chuii. Their recommendation is that larvae should be fed microalgae within 2 to3 hours of hatching.
- Mitchell, J.S. 2003. Mobility of Stichodactyla gigantea sea anemones and implications for resident false anemonefish, Amphiprion ocellaris. Environmental Biology of Fishes 66(1):85-90.
- Kirk, J.T.O. 2003. The vertical attenuation of irradiance as a function of the optical properties of water. Limnology and Oceanography 48(1):9-17.
- Al Horani, F.A., Al Moghrabi, S.M. and D. deBeer. 2003. The mechanism of calcification and its relationship to photosynthesis and respiration in the scleractinian coral Galaxea fasciularis. Marine Biology 142(3):419-426.
- Al Horani, F.A., Al Moghrabi, S.M. and D. deBeer. 2003. Microsensor study of photosynthesis and calcification in the scleractinian coral, Galaxea fasciularis: active internal carbon cycle. Journal of Experimental Marine Biology and Ecology 288(1):1-16.
- Echeverria, C.A. 2003. Black corals (Cnidaria: Anthozoa: Antipatharia): first records and a new species form the Brazilian coast. Revista de Biologia Tropical 59(3-4):1067-1079.
- Goffredo, S. and N.E. Chadwick-Furman. 2003. Comparative demography of mushroom corals (Scleractinia: Fungiidae) and Eilat, Red Sea. Marine Biology 142(3):411-418.
- Goulet T.L. and M.A. Coffroth. 2003.Stability of an octocoral-algal symbiosis over time and space. Marine Ecology Progress Series Vol. 250
- Lirman, D., Orlando, B., Macia, S., Manzello, D., Kaufman, L., Biber, P. and T. Jones. 2003. Coral communities of Biscayne Bay, Florida and adjacent offshore areas: diversity abundance, distribution and environmental correlates. Aquatic Conservation of Marine and Freshwater Ecosystems 13(2):121-136.
- Mate, J.L.. 2003. Ecological, genetic and morphological differences among the three Pavona (Cnidaria:Anthozoa) species from the Pacific coast of Panama. Marine Biology 142(3):426-440.
- Philipp, E and K. Fabricius. 2003. Photophysiological stress in scleractinian corals in response to short-term sedimentation. Journal of Experimental Marine Biology and Ecology 287:57-78.
- Stake, J.L. and P.W. Sammarco. 2003. Effects of pressure on swimming behavior in planulae of the coral Porites asteroides (Cnidaria, Scleractinia). Journal of Experimental Marine Biology and Ecology 288(1):181-203.
- Croquer, A., Villamizar, E. and N. Noriga. 2002. Environmental factors affecting tissue regeneration of the reef-building coral Montastrea annularis (Faviidae) at Los Roques National Park, Venezuela. Revista de Biologia Tropical 59(3-4):1055-1066.
- Frias-Lopez, J., Bonheyo, G.T., Jin, Q.S. and B.W. Forke. 2003. Cyanobacteria associated with black band disease in Caribbean and Indo-Pacific reefs. Applied and Environmental Microbiology 69(4):2409-?.
- Barak, Y., Cytryn, E., Gelfand, I., Krom, M. and J. van Rijn. 2003. Phosphorus removal in a marine prototype recirculating aquaculture system. Aquaculture 220(1-5):313-326.
- Cheney, K.L. and I.M. Cote. 2003. Habitat choice in adult longfin damselfish: territory characteristics and relocation times. Journal of Experimental Marine Biology and Ecology 287:1-12.
- Kirk, J.T.O. 2003. The vertical attenuation of irradiance as a function of the optical properties of water. Limnology and Oceanography 48(1):9-17.
- Asoh, K. 2003. Reproductive parameters of female Hawaiian damselfish Dascyllus albisella with comparison to other tropical and subtropical damselfishes. Marine Biology, DOI 10.1007/s00227-003-1108-6 Online publication: May 28, 2003 URL: http://dx.doi.org/10.1007/s00227-003-1108-6
- Calado, R., Narciso, L, Marcis, J., Rhyne, A.L. and J. Lin. 2003. A rearing system for the culture of ornamental decapod crustacean larvae. Aquaculture 218:329-339.
- Clarke, P.J., Kamatsu, T., Bell, J.D., Lasi, F., Oengpepa, C.P. and J. Legata.
- Combined culture of Trochus niloticus and giant clams (Tridacnidae): benefits for restocking and farming. Aquaculture 215:123-144.
- Job, S.D., Do, H.H., Meewig, J.J. and H.J. Hall. 2002. Culturing the oceanic seahorse, Hippocampus kuda. Aquaculture 214:333-341.
- Woods, C.M.C. 2003. Growth and survival of juvenile seahorse, Hippocampus abdominalis reared on live, frozen and artificial foods. Aquaculture 220(1-5):287-298.
- Woods, C.M.C. 2003. Effects of varying Artemia enrichment on growth and survival of juvenile seahorses, Hippocampus abdominalis. Aquaculture 220(1-5):537-548.
- Woods, C.M.C. 2003. Effects of stocking density and gender segregation in the seahorse Hippocampus abdominalis. Aquaculture 218:167-176.