(PART-1) HERE IS AN ARTICLE FOR THE INDIVIDUALS THAT JUST CAN'T GET ENOUGH ON LIGHTING WITH A SURPRISING CONCLUSION IN PART-2.
Lighting the Reef Aquarium - Spectrum or Intensity?
By Dana Riddle and Miguel Olaizola
It seems that avid reef aquaria hobbyists are constantly in search of a better lighting system. Perhaps one is motivated by a desire for more rapid coral growth, or simply an aquarium that is more pleasing to the eye. The question "What is the best lamp?" is often asked. Although the question is valid, the "best lamp" means different things among hobbyists. Is an aesthetically pleasing aquarium the goal, or is the promotion of photosynthesis the ultimate objective? The former is purely subjective. Finding an answer to the latter is quantifiable, but requires some rather sophisticated equipment. This article suggests an answer to the photosynthesis issue based on results of experiments conducted with a newly available research instrument.
Those factors promoting photosynthesis must be given serious attention since most tropical corals of interest to hobbyists contain symbiotic zooxanthellae algal cells. Of these factors, lighting is of primary importance. Debates have raged over which parameter, light intensity or spectral quality is more important. Both, of course, play a part in promoting photosynthesis in zooxanthellae. Light intensity or Photosynthetic Photon Flux Density (or PPFD, simply the number of light particles - photons - falling upon a given surface) must meet zooxanthellaes’ minimal requirements or the algal cells eventually die. If spectral quality is not correct, photosynthesis is not promoted and zooxanthellae become "starved" for proper light and will soon perish.
Estimating the spectral requirements of zooxanthellae is not particularly easy. Zooxanthellae contain various photosynthetic pigments, including chlorophyll A, chlorophyll C2, the carotenoid peridinin and perhaps others (all of which may be in varying proportions due to the photoadaptive capabilities of zooxanthellae). However, researchers have established the quality of light absorbed by these pigments and we can safely assume certain wavelengths are required.
To believe that blue (430-480 nm) and red (600- 700 nm) wavelengths are required is only partially true. A wide range of wavelengths are absorbed by chlorophylls A and C2; however, peridinin and perhaps other photopigments, effectively harvest light energy outside of the range normally associated with photosynthesis.
Researchers have addressed light quality and its effects on zooxanthellae and coral growth. Perhaps the most interesting is a paper by Kinzie et al. (1984); they presented evidence that corals grown more rapidly under blue and white light of the same intensities (~12% of solar Photosynthetically Active Radiation - PAR, ~250 µMols·m2·sec, or 10,000 lux) than under "green" or "red" light of equal intensities. These scientists used clear or colored acrylic filters and natural sunlight. The blue filter transmitted wavelengths of ~ 400 to 500 nm and the clear filter (transmission quality not shown in the paper) likely was a fair representation of sunlight (although most acrylics attenuate all wavelengths but tend to decrease violet and blue disproportionately). "Blue" light is suggested to have some rather "magical" properties - it has been noted to increase rates of protein synthesis in some algae, as well as cause shifts in photosynthetic pigment concentrations in zooxanthellae. Blue light has also been reported to increase rates of photosynthesis (Kinzie and Hunter, 1987). Are spectral characteristics of "blue" metal halide lamps sufficient to promote photosynthesis more efficiently in zooxanthellae of captive corals?
Unfortunately, the spectral qualities of light transmitted by these researchers’ filters only faintly resemble those of lights used over aquaria. It is a leap of faith to apply the results obtained under filtered sunlight to artificial light sources, which have spectral spikes. However, this has not stopped many from interpreting that higher Kelvin lamps are best for promoting photosynthesis in corals.
In an excellent series of articles, Joshi and Morgan (1998; 1999) presented spectral qualities of many metal halide lamps commonly sold in the pet industry, but stopped short of making recommendations to hobbyists. So, the question remains - are there major advantages to zooxanthellae/corals when using certain lamps, or is there only aesthetic appeal? Do common lamps with output weighted in the violet/blue regions of the spectrum and readily available to hobbyists actually increase the rates of photosynthesis?
Two lamps were chosen for use in an experiment designed to determine if differing spectral qualities do indeed make a difference in photosynthesis rates. The first lamp is a Philips 175-watt 4,000° K metal halide lamp (usually available for less than $20 in major home improvement centers). The second lamp is an Aquarium Lighting Systems 175-watt 12,000°K "Sunburst" metal halide lamp. Spectral signatures of these lamps were determined with an Ocean Optics spectrometer. Spectral compositions were estimated by use of a LiCor quantum meter and glass cut-off filters. Use of these filters provides reasonable estimates of violet and blue wavelengths (400-465 nm) and red wavelengths (600-700 nm). These filters transmit few wavelengths in the yellow and orange portion of the spectrum. Considering that metal halide lamps have spectral spikes at 575 and 577 nm (due to the element mercury contained within the arc tubes), However, the Sunburst 12,000°K lamp is the "bluest;" the Philips lamp less so.
There are many ways to estimate the effectiveness of light on corals. If one has the time and patience, simple observations of growth (along with rigorous control of other factors) may suffice. A more sophisticated approach is one using a respirometer and delta oxygen evolution as the metric in judging rates of photosynthesis. Preliminary results suggested there is no benefit to photosynthesis when using a 20,000°K metal halide lamp as opposed to the use of an inexpensive halide lamp (Riddle and Amussen, 1999). However, respirometry is an inexact science, fraught with all the drawbacks of experiments conducted in small, sealed experimental chambers.
A new technique is now available - that of Pulsed Amplitude Modulation (PAM) fluorometry. This experiment employed a Mini-PAM meter, manufactured by Walz GmbH, Germany. This method is non-intrusive and is gaining acceptance as the preferred method of measuring rates of photosynthesis (Beer et al., 1998). The Mini-PAM measures the fluorescence yield of the chlorophyll A molecules in the photosystem of zooxanthellae in response to changes in illumination. Chlorophyll fluorescence is assumed to arise from reradiation of absorbed light energy from Photosystem II (PS II) antenna pigments (including chlorophyll A, chlorophyll C2, and peridinin).
Fluorescence and the photochemical reactions of photosynthesis are competing processes in the dissipation of absorbed light energy. Energy absorbed by antenna pigments is generally assumed to have three primary pathways for dissipation. First, it can be reradiated (fluoresced); second, it can be dissipated as heat or, third, it can be transferred to the reaction center of PS II. Once in the reaction center, this energy is available for use in photochemistry. Reduction -oxidation potential of the primary quinone acceptor (QA) governs what happens next. If the Qa is oxidized (the reaction center is said to be "open"), a photochemical reaction will occur and eventually lead to oxygen evolution and carbon fixation, the events that we associate with photosynthesis. However, if the QA is reduced (the reaction center is "closed") the energy cannot be used in photochemistry. Therefore the chances of thermal dissipation and fluorescence will increase.
Thus, the magnitude of the fluorescence signal depends mainly on the amount of light energy absorbed (which itself depends on the spectral quality and intensity of the illumination source and the quantity and absorption spectra of the photosynthetic pigments present in the cells) and the fraction of reaction centers that are open.
The Mini-PAM exploits the relationship between photochemistry and fluorescence, and how it changes under different illumination conditions, to estimate the capacity of photosynthetic cells to photosynthesize (i.e., the fraction of reaction centers that are open). Essentially the Mini-PAM estimates the fraction of reaction centers that are open by comparing the magnitude of the fluorescence signal under ambient illumination (e.g., different lamps or sunlight) and the magnitude of the fluorescence signal following a saturating flash of light that temporarily overwhelms PS II and closes all the reaction centers.
(CONT. PART-2)
Lighting the Reef Aquarium - Spectrum or Intensity?
By Dana Riddle and Miguel Olaizola
It seems that avid reef aquaria hobbyists are constantly in search of a better lighting system. Perhaps one is motivated by a desire for more rapid coral growth, or simply an aquarium that is more pleasing to the eye. The question "What is the best lamp?" is often asked. Although the question is valid, the "best lamp" means different things among hobbyists. Is an aesthetically pleasing aquarium the goal, or is the promotion of photosynthesis the ultimate objective? The former is purely subjective. Finding an answer to the latter is quantifiable, but requires some rather sophisticated equipment. This article suggests an answer to the photosynthesis issue based on results of experiments conducted with a newly available research instrument.
Those factors promoting photosynthesis must be given serious attention since most tropical corals of interest to hobbyists contain symbiotic zooxanthellae algal cells. Of these factors, lighting is of primary importance. Debates have raged over which parameter, light intensity or spectral quality is more important. Both, of course, play a part in promoting photosynthesis in zooxanthellae. Light intensity or Photosynthetic Photon Flux Density (or PPFD, simply the number of light particles - photons - falling upon a given surface) must meet zooxanthellaes’ minimal requirements or the algal cells eventually die. If spectral quality is not correct, photosynthesis is not promoted and zooxanthellae become "starved" for proper light and will soon perish.
Estimating the spectral requirements of zooxanthellae is not particularly easy. Zooxanthellae contain various photosynthetic pigments, including chlorophyll A, chlorophyll C2, the carotenoid peridinin and perhaps others (all of which may be in varying proportions due to the photoadaptive capabilities of zooxanthellae). However, researchers have established the quality of light absorbed by these pigments and we can safely assume certain wavelengths are required.
To believe that blue (430-480 nm) and red (600- 700 nm) wavelengths are required is only partially true. A wide range of wavelengths are absorbed by chlorophylls A and C2; however, peridinin and perhaps other photopigments, effectively harvest light energy outside of the range normally associated with photosynthesis.
Researchers have addressed light quality and its effects on zooxanthellae and coral growth. Perhaps the most interesting is a paper by Kinzie et al. (1984); they presented evidence that corals grown more rapidly under blue and white light of the same intensities (~12% of solar Photosynthetically Active Radiation - PAR, ~250 µMols·m2·sec, or 10,000 lux) than under "green" or "red" light of equal intensities. These scientists used clear or colored acrylic filters and natural sunlight. The blue filter transmitted wavelengths of ~ 400 to 500 nm and the clear filter (transmission quality not shown in the paper) likely was a fair representation of sunlight (although most acrylics attenuate all wavelengths but tend to decrease violet and blue disproportionately). "Blue" light is suggested to have some rather "magical" properties - it has been noted to increase rates of protein synthesis in some algae, as well as cause shifts in photosynthetic pigment concentrations in zooxanthellae. Blue light has also been reported to increase rates of photosynthesis (Kinzie and Hunter, 1987). Are spectral characteristics of "blue" metal halide lamps sufficient to promote photosynthesis more efficiently in zooxanthellae of captive corals?
Unfortunately, the spectral qualities of light transmitted by these researchers’ filters only faintly resemble those of lights used over aquaria. It is a leap of faith to apply the results obtained under filtered sunlight to artificial light sources, which have spectral spikes. However, this has not stopped many from interpreting that higher Kelvin lamps are best for promoting photosynthesis in corals.
In an excellent series of articles, Joshi and Morgan (1998; 1999) presented spectral qualities of many metal halide lamps commonly sold in the pet industry, but stopped short of making recommendations to hobbyists. So, the question remains - are there major advantages to zooxanthellae/corals when using certain lamps, or is there only aesthetic appeal? Do common lamps with output weighted in the violet/blue regions of the spectrum and readily available to hobbyists actually increase the rates of photosynthesis?
Two lamps were chosen for use in an experiment designed to determine if differing spectral qualities do indeed make a difference in photosynthesis rates. The first lamp is a Philips 175-watt 4,000° K metal halide lamp (usually available for less than $20 in major home improvement centers). The second lamp is an Aquarium Lighting Systems 175-watt 12,000°K "Sunburst" metal halide lamp. Spectral signatures of these lamps were determined with an Ocean Optics spectrometer. Spectral compositions were estimated by use of a LiCor quantum meter and glass cut-off filters. Use of these filters provides reasonable estimates of violet and blue wavelengths (400-465 nm) and red wavelengths (600-700 nm). These filters transmit few wavelengths in the yellow and orange portion of the spectrum. Considering that metal halide lamps have spectral spikes at 575 and 577 nm (due to the element mercury contained within the arc tubes), However, the Sunburst 12,000°K lamp is the "bluest;" the Philips lamp less so.
There are many ways to estimate the effectiveness of light on corals. If one has the time and patience, simple observations of growth (along with rigorous control of other factors) may suffice. A more sophisticated approach is one using a respirometer and delta oxygen evolution as the metric in judging rates of photosynthesis. Preliminary results suggested there is no benefit to photosynthesis when using a 20,000°K metal halide lamp as opposed to the use of an inexpensive halide lamp (Riddle and Amussen, 1999). However, respirometry is an inexact science, fraught with all the drawbacks of experiments conducted in small, sealed experimental chambers.
A new technique is now available - that of Pulsed Amplitude Modulation (PAM) fluorometry. This experiment employed a Mini-PAM meter, manufactured by Walz GmbH, Germany. This method is non-intrusive and is gaining acceptance as the preferred method of measuring rates of photosynthesis (Beer et al., 1998). The Mini-PAM measures the fluorescence yield of the chlorophyll A molecules in the photosystem of zooxanthellae in response to changes in illumination. Chlorophyll fluorescence is assumed to arise from reradiation of absorbed light energy from Photosystem II (PS II) antenna pigments (including chlorophyll A, chlorophyll C2, and peridinin).
Fluorescence and the photochemical reactions of photosynthesis are competing processes in the dissipation of absorbed light energy. Energy absorbed by antenna pigments is generally assumed to have three primary pathways for dissipation. First, it can be reradiated (fluoresced); second, it can be dissipated as heat or, third, it can be transferred to the reaction center of PS II. Once in the reaction center, this energy is available for use in photochemistry. Reduction -oxidation potential of the primary quinone acceptor (QA) governs what happens next. If the Qa is oxidized (the reaction center is said to be "open"), a photochemical reaction will occur and eventually lead to oxygen evolution and carbon fixation, the events that we associate with photosynthesis. However, if the QA is reduced (the reaction center is "closed") the energy cannot be used in photochemistry. Therefore the chances of thermal dissipation and fluorescence will increase.
Thus, the magnitude of the fluorescence signal depends mainly on the amount of light energy absorbed (which itself depends on the spectral quality and intensity of the illumination source and the quantity and absorption spectra of the photosynthetic pigments present in the cells) and the fraction of reaction centers that are open.
The Mini-PAM exploits the relationship between photochemistry and fluorescence, and how it changes under different illumination conditions, to estimate the capacity of photosynthetic cells to photosynthesize (i.e., the fraction of reaction centers that are open). Essentially the Mini-PAM estimates the fraction of reaction centers that are open by comparing the magnitude of the fluorescence signal under ambient illumination (e.g., different lamps or sunlight) and the magnitude of the fluorescence signal following a saturating flash of light that temporarily overwhelms PS II and closes all the reaction centers.
(CONT. PART-2)
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