stony_corals
New member
I emailed Pohl and he didn't respond.... IMHO, the blue is closer to 420NM than 450nm (UVL SA vs. ATI B+).....
Lighting Wavelengths
- Thread starter snaza
- Start date
Todd March
Premium Member
Yeah I agree--the FJP fluoresces GFP's almost as well as my G-Mann True Actinics, really surprised me...
MCsaxmaster
New member
Ok, admittedly I've only skimmed this thread, but I'll toss out some thoughts, for what they're worth. Apologies for the length too. This Wikipedia article should be helpful in understanding and visualizing the processes I’m describing: http://en.wikipedia.org/wiki/Photosynthesis
Step 1 in photosynthesis is to capture photons. When a photon is absorbed it excites an electron from a low energy level to a higher energy level. It takes a particular quanta of energy to do this (though there is a bit of “wiggle room†in the wavelength that can be absorbed due to electron vibration), which is why specific photopigments only absorb around specific wavelengths. Once the electron is excited the energy is passed from electron to electron (through the antenna proteins) and to the reaction center of photosystem II (PSII). The reaction center includes a molecule of chlorophyll a and numerous proteins.
So step 2 of photosynthesis is transferring the energy from absorbed photons down antenna proteins to the reaction center of PSII.
Step 3 of photosynthesis is using that absorbed energy to do some work. An electron from the chl a in the reaction center is excited and transferred to a carrier protein. That leaves the reaction center oxidized (= lacking an electron). The same process happens 3 more times for a loss of 4 electrons total. Again, those electrons get transferred from the reaction center to a carrier protein (e.g., plastoquinone). Having lost 4 e- the reaction center needs to get back some electrons. To do that it splits 2 water molecules as in the reaction below:
2H2O = 4e- + O2 + 4H+
Doing so produces the 4 needed e-, reducing PSII. It also produces molecular oxygen and 4 protons. The protons are used later to produce ATP and the ATP is used to produce carbohydrates and do other cellular work.
To this point we still haven’t fixed any carbon, and we’re about half way toward having accomplished photosynthesis.
Step 4 of photosynthesis is transporting the electrons we generated above down an electron transport chain to photosystem I (PSI). At PSI similar processes of photon absorption, energy transfer, electron excitation and charge separation take place. Electrons are transferred from PSI to NADP. They are replaced by e- coming down the electron transport chain to PSI. NADP is reduced at PSI to NADPH by ferredoxin using the e- from PSI and an H+. NADPH is used as a reducing agent in various cellular activities, including carbon fixation.
Step 5 of photosynthesis is using the ATP generated above (H+ produced at PSII used to generate ATP) and the NADPH generated above (produced at PSI) to take CO2 and turn it into carbohydrates using the Calvin cycle.
Summarizing, for photosynthesis to happen we need 5 major steps to take place:
1) Absorb photons in antenna proteins of PSII.
2) Transfer the energy from the photons to PSII, use that energy to electrons from PSII to a carrier protein.
3) Replace those electrons by slitting water, and use the H+ that results to make ATP.
4) Transfer electrons from PSII down the electron transport chain to PSI. At PSI transfer electrons to NADP with ferrodoxin and H+ to make NADPH.
5) Use the ATP from PSII and the NADPH from PSI to fuel the Calvin cycle, turning CO2 into carbohydrates.
There are several conditions that can limit the rate of photosynthesis for a given organism at a given temperature:
1) The supply of photons to drive the whole process.
2) The supply of carrier proteins (plastoquinone) at PSII to take up and transfer electrons down the electron transport chain.
3) The supply of CO2.
The rate that photons are captured by PSII depends on two things:
a) the number of photons available (in other words, PAR/PPFD)
b) wavelength-specific absorption of those photons by photosynthetic pigments/accessory pigments
As you can see in the action spectrum on the previous page, the zooxanthellae in corals are best at absorbing "blue" photons, good at absorbing "violet", "cyan", and "red-orange" and aren't as good at absorbing "yellow" or "green" photons.
The particular action spectra depicted above is a bit more "spikey" than I would say is common for most corals. In other words, the difference in the likelihood of absorbing a blue vs. a green vs. a red photon in most zooxanthellae is somewhat small--smaller than depicted above. Of course, it depends on the suite of pigments the zooxanthellae are producing. Different zoox. in different situations, or the same zoox. in different situations, will have slightly different action spectra. As a side-note: zooxanthellae look brown because they are reflecting a mix of wavelengths heavy in the green, yellow and orange. Green plants have much “spikier†action spectra than dinoflagellates: they absorb heavily in the blue, violet, and red, and reflect heavily in the green and yellow. Hence, green plants look green and zooxanthellae look brown.
If we use the action spectrum above as a guide, the coral depicted above is about 4x as likely to absorb a blue photon as a yellow photon. It is about 3x as likely to absorb a red photon as a yellow photon, and about 3/4x as likely to absorb a red photon as a blue photon.
A critically important point to consider that I’ll make here is that absorbing photons IS NOT equivalent to performing photosynthesis. It is merely the first step.
Let’s compare what happens at high levels to what happens at low light levels. With high light levels most of the reaction centers of PSII in a cell will have absorbed a photon and will have an excited electron ready to be transferred down the electron transport chain. At low light levels many of the reaction centers will not have absorbed a photon (simply because there are fewer photons available to absorb) and fewer will be ready to transport an electron.
The amount of time it takes for a photon to be absorbed by antenna proteins and transferred to PSII is very, very short (~10^-12 seconds). The amount of time it takes to transport an electron down the e- transport chain is still very short, but comparatively much longer (~10^-9 seconds)â€"about 1000x as long.
When the energy from a photon is transferred to PSII and an electron is excited, the electron only remains in that excited state for a short period of time (~10^-9 sec or less). If the electron is transferred to plastoquinone during that time it can be used in photosynthesis. However, if a plastoquinone molecule doesn’t get there in time then the electron falls back to its ground state. The energy from the absorbed photon is lost as heat and/or fluorescence and thereby doesn’t get used for photosynthesis.
When light levels are low there is lots of plastoquinone relative to the number of reaction centers that have excited electrons, so most of the energy can be put into photosynthesis. However, as more and more reaction centers absorb photons the plastoquinone pool starts missing more and more of the excited electrons before they return to the ground state. Eventually we reach a point where the electron transport chain is transferring electrons as fast as it possibly can. If we increase the light intensity we will continue to see more light absorbed, but that light energy is simply lost as fluorescence and heat and not put into photochemistry.
It takes a particular quanta of energy to excite and electron in PSII so that it can be transferred down the e- transport chain. If a photon has less energy than is required it can’t be used in photochemistry at all (e.g., less than ~700 nm). If, however, the photon yields more energy than is required to excite the electron in PSII the extra energy is lost from PSII as heat and fluorescence. Once a photon is absorbed it is doesn’t matter one bit what the wavelength was. A blue photon a green photon and a red photon can all excite exactly the same number of photons in PSII: one electron.
If the light intensity is high then the rate of photosynthesis will be limited by something such as the rate that electrons can be transported down the e- transport chain, not by a lack of light. If we have high light intensity of blue light then the zoox. will absorb more of the photon than they will with high intensity green light. However, since photosynthesis is not light-limited in this case, it doesn’t affect the rate of photosynthesis one way or the other (although, we could start to see photoinhibition if FAR more photons are absorbed than can be used).
If we are at or above the point of photosaturation, the spectrum of the light is therefore entirely irrelevant. If the organisms absorb more light, they will just dump more energy as heat and fluorescence. If they absorb less light they will dump less energy. They simply have no way to do anything with this additional energy.
Now, if we consider what happens at low light levels, then we have a somewhat different situation. Here we are light-limited. If more light is absorbed it WILL result in increased photosynthesis. Hence, at low light levels blue light may indeed yield higher rates of photosynthesis than green light. Practically speaking, given typical action spectra in zooxanthellae, the difference is so small it has essentially negligible effects considering what we as aquarists are trying to do (namely grow corals and such).
How to translate this into actually putting a light over an aquarium… Well, at higher light intensity, spectrum is irrelevant considering the spectrum of any bulb we might consider using. If the corals aren’t light limited, it simply doesn’t matter if they are absorbing lots and lots of blue photons, or a mix of fewer blue, violet, green, and red photons. They are getting as much light as they can use, and that’s that.
At low light levels spectrum may indeed matter, but not whole lot given the spectra of bulbs we use and typical action spectra for zooxanthellae.
If, however, we consider different spectra at DIFFERENT intensities (e.g., a bright 10 K metal halide vs. a dimmer 15 K halide…dimmer = lower PAR/PPFD) then we have a more complicated situation. To determine which bulb would produce higher rates of photosynthesis at potentially limiting light intensities we would need to determine the amount of photosynthetically usuable radiation (PUR). To do so we can integrate the product of PAR at each wavelength and the likelihood of absorption at that wavelength over the range of 400-750 nm. Since the action spectrum is plastic over time even in an individual organism, and certainly varies among organisms, we really can’t find one end-all be-all PUR value for a lamp that will be useful for different organisms, or even the same organism in different situations.
Having said that, typically the difference in intensity between lower Kelvn but brighter bulbs and higher Kelvin but dimmer bulbs is so great that the potential benefit of a more favorable spectrum is simply overwhelmed by the difference in intensity. But again, the difference in spectrum can only potentially make a difference at low intensity. At higher intensity (near photosaturation) spectrum doesn’t matter at all. At that point there is so much light the efficiency of absorption is simply irrelevant.
Chris
Step 1 in photosynthesis is to capture photons. When a photon is absorbed it excites an electron from a low energy level to a higher energy level. It takes a particular quanta of energy to do this (though there is a bit of “wiggle room†in the wavelength that can be absorbed due to electron vibration), which is why specific photopigments only absorb around specific wavelengths. Once the electron is excited the energy is passed from electron to electron (through the antenna proteins) and to the reaction center of photosystem II (PSII). The reaction center includes a molecule of chlorophyll a and numerous proteins.
So step 2 of photosynthesis is transferring the energy from absorbed photons down antenna proteins to the reaction center of PSII.
Step 3 of photosynthesis is using that absorbed energy to do some work. An electron from the chl a in the reaction center is excited and transferred to a carrier protein. That leaves the reaction center oxidized (= lacking an electron). The same process happens 3 more times for a loss of 4 electrons total. Again, those electrons get transferred from the reaction center to a carrier protein (e.g., plastoquinone). Having lost 4 e- the reaction center needs to get back some electrons. To do that it splits 2 water molecules as in the reaction below:
2H2O = 4e- + O2 + 4H+
Doing so produces the 4 needed e-, reducing PSII. It also produces molecular oxygen and 4 protons. The protons are used later to produce ATP and the ATP is used to produce carbohydrates and do other cellular work.
To this point we still haven’t fixed any carbon, and we’re about half way toward having accomplished photosynthesis.
Step 4 of photosynthesis is transporting the electrons we generated above down an electron transport chain to photosystem I (PSI). At PSI similar processes of photon absorption, energy transfer, electron excitation and charge separation take place. Electrons are transferred from PSI to NADP. They are replaced by e- coming down the electron transport chain to PSI. NADP is reduced at PSI to NADPH by ferredoxin using the e- from PSI and an H+. NADPH is used as a reducing agent in various cellular activities, including carbon fixation.
Step 5 of photosynthesis is using the ATP generated above (H+ produced at PSII used to generate ATP) and the NADPH generated above (produced at PSI) to take CO2 and turn it into carbohydrates using the Calvin cycle.
Summarizing, for photosynthesis to happen we need 5 major steps to take place:
1) Absorb photons in antenna proteins of PSII.
2) Transfer the energy from the photons to PSII, use that energy to electrons from PSII to a carrier protein.
3) Replace those electrons by slitting water, and use the H+ that results to make ATP.
4) Transfer electrons from PSII down the electron transport chain to PSI. At PSI transfer electrons to NADP with ferrodoxin and H+ to make NADPH.
5) Use the ATP from PSII and the NADPH from PSI to fuel the Calvin cycle, turning CO2 into carbohydrates.
There are several conditions that can limit the rate of photosynthesis for a given organism at a given temperature:
1) The supply of photons to drive the whole process.
2) The supply of carrier proteins (plastoquinone) at PSII to take up and transfer electrons down the electron transport chain.
3) The supply of CO2.
The rate that photons are captured by PSII depends on two things:
a) the number of photons available (in other words, PAR/PPFD)
b) wavelength-specific absorption of those photons by photosynthetic pigments/accessory pigments
As you can see in the action spectrum on the previous page, the zooxanthellae in corals are best at absorbing "blue" photons, good at absorbing "violet", "cyan", and "red-orange" and aren't as good at absorbing "yellow" or "green" photons.
The particular action spectra depicted above is a bit more "spikey" than I would say is common for most corals. In other words, the difference in the likelihood of absorbing a blue vs. a green vs. a red photon in most zooxanthellae is somewhat small--smaller than depicted above. Of course, it depends on the suite of pigments the zooxanthellae are producing. Different zoox. in different situations, or the same zoox. in different situations, will have slightly different action spectra. As a side-note: zooxanthellae look brown because they are reflecting a mix of wavelengths heavy in the green, yellow and orange. Green plants have much “spikier†action spectra than dinoflagellates: they absorb heavily in the blue, violet, and red, and reflect heavily in the green and yellow. Hence, green plants look green and zooxanthellae look brown.
If we use the action spectrum above as a guide, the coral depicted above is about 4x as likely to absorb a blue photon as a yellow photon. It is about 3x as likely to absorb a red photon as a yellow photon, and about 3/4x as likely to absorb a red photon as a blue photon.
A critically important point to consider that I’ll make here is that absorbing photons IS NOT equivalent to performing photosynthesis. It is merely the first step.
Let’s compare what happens at high levels to what happens at low light levels. With high light levels most of the reaction centers of PSII in a cell will have absorbed a photon and will have an excited electron ready to be transferred down the electron transport chain. At low light levels many of the reaction centers will not have absorbed a photon (simply because there are fewer photons available to absorb) and fewer will be ready to transport an electron.
The amount of time it takes for a photon to be absorbed by antenna proteins and transferred to PSII is very, very short (~10^-12 seconds). The amount of time it takes to transport an electron down the e- transport chain is still very short, but comparatively much longer (~10^-9 seconds)â€"about 1000x as long.
When the energy from a photon is transferred to PSII and an electron is excited, the electron only remains in that excited state for a short period of time (~10^-9 sec or less). If the electron is transferred to plastoquinone during that time it can be used in photosynthesis. However, if a plastoquinone molecule doesn’t get there in time then the electron falls back to its ground state. The energy from the absorbed photon is lost as heat and/or fluorescence and thereby doesn’t get used for photosynthesis.
When light levels are low there is lots of plastoquinone relative to the number of reaction centers that have excited electrons, so most of the energy can be put into photosynthesis. However, as more and more reaction centers absorb photons the plastoquinone pool starts missing more and more of the excited electrons before they return to the ground state. Eventually we reach a point where the electron transport chain is transferring electrons as fast as it possibly can. If we increase the light intensity we will continue to see more light absorbed, but that light energy is simply lost as fluorescence and heat and not put into photochemistry.
It takes a particular quanta of energy to excite and electron in PSII so that it can be transferred down the e- transport chain. If a photon has less energy than is required it can’t be used in photochemistry at all (e.g., less than ~700 nm). If, however, the photon yields more energy than is required to excite the electron in PSII the extra energy is lost from PSII as heat and fluorescence. Once a photon is absorbed it is doesn’t matter one bit what the wavelength was. A blue photon a green photon and a red photon can all excite exactly the same number of photons in PSII: one electron.
If the light intensity is high then the rate of photosynthesis will be limited by something such as the rate that electrons can be transported down the e- transport chain, not by a lack of light. If we have high light intensity of blue light then the zoox. will absorb more of the photon than they will with high intensity green light. However, since photosynthesis is not light-limited in this case, it doesn’t affect the rate of photosynthesis one way or the other (although, we could start to see photoinhibition if FAR more photons are absorbed than can be used).
If we are at or above the point of photosaturation, the spectrum of the light is therefore entirely irrelevant. If the organisms absorb more light, they will just dump more energy as heat and fluorescence. If they absorb less light they will dump less energy. They simply have no way to do anything with this additional energy.
Now, if we consider what happens at low light levels, then we have a somewhat different situation. Here we are light-limited. If more light is absorbed it WILL result in increased photosynthesis. Hence, at low light levels blue light may indeed yield higher rates of photosynthesis than green light. Practically speaking, given typical action spectra in zooxanthellae, the difference is so small it has essentially negligible effects considering what we as aquarists are trying to do (namely grow corals and such).
How to translate this into actually putting a light over an aquarium… Well, at higher light intensity, spectrum is irrelevant considering the spectrum of any bulb we might consider using. If the corals aren’t light limited, it simply doesn’t matter if they are absorbing lots and lots of blue photons, or a mix of fewer blue, violet, green, and red photons. They are getting as much light as they can use, and that’s that.
At low light levels spectrum may indeed matter, but not whole lot given the spectra of bulbs we use and typical action spectra for zooxanthellae.
If, however, we consider different spectra at DIFFERENT intensities (e.g., a bright 10 K metal halide vs. a dimmer 15 K halide…dimmer = lower PAR/PPFD) then we have a more complicated situation. To determine which bulb would produce higher rates of photosynthesis at potentially limiting light intensities we would need to determine the amount of photosynthetically usuable radiation (PUR). To do so we can integrate the product of PAR at each wavelength and the likelihood of absorption at that wavelength over the range of 400-750 nm. Since the action spectrum is plastic over time even in an individual organism, and certainly varies among organisms, we really can’t find one end-all be-all PUR value for a lamp that will be useful for different organisms, or even the same organism in different situations.
Having said that, typically the difference in intensity between lower Kelvn but brighter bulbs and higher Kelvin but dimmer bulbs is so great that the potential benefit of a more favorable spectrum is simply overwhelmed by the difference in intensity. But again, the difference in spectrum can only potentially make a difference at low intensity. At higher intensity (near photosaturation) spectrum doesn’t matter at all. At that point there is so much light the efficiency of absorption is simply irrelevant.
Chris
DheereCrossing
New member
I can't believe I made it through Chris's post on photosysnthesis. I had to read it twice but it answers exactly what a lot of people are asking but can't/won't bother to understand. "What light should I buy?" "Just tell me which one, I don't want to read a bunch of stuff."
So is this lost energy what causes the stress to corals resulting in "bleaching"?
Does the coral itself increase in temperature?
If so, then wouldn't having a large amount of corals losing that energy from intense light increase the temperature of the entire tank causing more heat problems along with the light source emitting heat itself?
As much as all of this information helps me to "understand" it all, how do I know what is best for my aquarium? In a propagation system where I have genus and species specific tanks is it different educated guess-and-checks to see what works or should I just be happy with what I've got if my corals look happy?
Zimster
Member
Please correct me if i am wrong......
Bleaching just results from zooxanthellae being expelled from the coral tissue. Corals can expel "60-90% of their zooxanthellae and each zooxanthellae may lose 50-80% of its photosynthetic pigments" when bleaching occurs.
The most common cause of bleaching is something shocking the coral or causing stress on it, such as:
- changing salinity
- extreme temperature swings
- pH being too low
- silt
- extremely low nutrient levels
- sudden increase in lighting conditions
- infection
- chemicals
I believe that the most common factor that causes bleaching is light and temperature.
Say you get a new light for your tank. Let's say you are upgrading from power compacts to metal halide fixtures. The PAR levels will be extremely different. Since the corals you currently have are used to the lower light levels, they will have more zooxanthellae to produce more energy. With the sudden change in lighting conditions, the zooxanthellae will overproduce carbs for the coral, and cause the coral tissue to bloat up. To try to prevent itself from actually blowing up, it will expel its zooxanthellae and bleach.
I believe that if the coral has been quarantined and has had a chance to get used to certain lighting conditions, the lost energy from photosynthesis just goes into making fluorescence and heat. Usually only a sudden change in lighting conditions will cause a coral bleach. Corals won't bleach from the light if they are used to it.
I am not sure about having more corals causing heat problems....do they distribute that much heat??
Bleaching just results from zooxanthellae being expelled from the coral tissue. Corals can expel "60-90% of their zooxanthellae and each zooxanthellae may lose 50-80% of its photosynthetic pigments" when bleaching occurs.
The most common cause of bleaching is something shocking the coral or causing stress on it, such as:
- changing salinity
- extreme temperature swings
- pH being too low
- silt
- extremely low nutrient levels
- sudden increase in lighting conditions
- infection
- chemicals
I believe that the most common factor that causes bleaching is light and temperature.
Say you get a new light for your tank. Let's say you are upgrading from power compacts to metal halide fixtures. The PAR levels will be extremely different. Since the corals you currently have are used to the lower light levels, they will have more zooxanthellae to produce more energy. With the sudden change in lighting conditions, the zooxanthellae will overproduce carbs for the coral, and cause the coral tissue to bloat up. To try to prevent itself from actually blowing up, it will expel its zooxanthellae and bleach.
I believe that if the coral has been quarantined and has had a chance to get used to certain lighting conditions, the lost energy from photosynthesis just goes into making fluorescence and heat. Usually only a sudden change in lighting conditions will cause a coral bleach. Corals won't bleach from the light if they are used to it.
I am not sure about having more corals causing heat problems....do they distribute that much heat??
Last edited:
greenbean36191
Premium Member
No. Light/temperature induced bleaching is a reaction to oxidative stress. Aside from normal molecular oxygen, photosynthesis also produces small amounts of what are known as reactive oxygen species (ROS) like hydroxide, peroxide, and superoxide radicals. These molecules attack cell membranes, proteins, and nucleic acids in the tissues, eventually leading to death. Under normal conditions, these are produced in very low levels so they either diffuse out of the tissue or are neutralized by antioxidants before they cause damage. If you increase the temperature of the water or increase the lighting intensity you get more photosynthesis and more production of ROS. If ROS production exceeds the ability for them to diffuse out of the tissue and the corals' ability to neutralize them, you start to get accumulation of damage in the cells and they start to die.
It's negligible and you're not going to be able to measure the change. It's so small and water is such a good conductor of heat the difference is effectively 0. You can get measurable increases in temp due to radiant heating though.
I didn't mean for it to be mean or anything....i was just posting a thought also....
MCsaxmaster
New member
Agreed with Mike above. I'll add just a few words.
Bleaching occurs when the zooxanthellae become severely damaged from some sort of stressor. In natural situations this stress usually results from severe oxidative stress, that is, when reactive oxygen species are produced in the chloroplasts of the zooxanthellae and start oxidizing (= destroying) everything they come in contact with. The ROS that cause that stress can directly and signifcantly damage the coral tissues, which is one reason corals bleach when their zoox. get really monkied up. There are a variety of mechanisms that can lead to that oxidative stress.
For example, when corals undergo photobleaching (from a sudden increase in light intensity) they end up collecting far more photons than they can use in photochemistry. Hence, they have a lot of excited (= high energy) electrons that are not quenched photochemically. Photosynthetic organisms have means of quenching some of those electrons via the xanthophyll cycle (termed "nonphotochemical quenching), thereby preventing the production of ROS by those electrons. Some of that energy will also be quenched via fluorescence.
While the process of e- transport down the e- transport chain is very efficient, some e- always end up getting "lost" down the path. Due to the high concentration of O2 in the area, that makes it conducive for the production of ROS. When we have high light relative to what the organism is adapted to we have more electrons that are NOT quenched photochemically and the potential for more of them to get "lost", leading to more ROS produced and making for badness.
When zooxanthellae experience temperature stress (or other organisms too) the lipids that make up the thylakoid membrane become more fluid. Think about butter in the refrigerator vs. room temperature vs. in the oven. As the temperature increases the membranes begin to melt. For the e- transport chain to work the proteins have to be spatially arranged in a very precise configuration. As the thylakoid membrane becomes more fluid (= melts) the proteins imbedded in it end up in incorrect configurations. Hence, more and more of those excited electrons get lost, create ROS, and badness ensues. A friend of mine actually studied this aspect of bleaching physiology for her MS thesis and got incredibly interesting results.
Increased UV, some viruses, some sfungal infection, some herbicides, etc. can also produce more ROS in plants via a several known pathways.
Hence, while the mechanism that leads to ROS production varies in, for example, high light stress vs. temperature stress, the result is effectively the same. To the zooxanthellae in a coral, temperature stress effectively "feels" like high light stress (although elevated temperature can and does harm other processes as well).
Agreed about the heat produced via non-photochemical quenching as being inconsequential in any normal circumstance. There simply isn't enough energy lost through this mechanism to heat the coral appreciably. Along these lines, however, some people have in fact measured temperature differences in dark colored vs. light colored corals in nature. The dark corals absorb more visible and IR radiation and have been measured at up to a couple of degrees C above ambient in nature in relatively stagnant water flow. However, that only becomes important when ambient temperatures are at or above normal thermal limits (for most corals in nature those limits are temperatures sustained in the range of ~86-95 F for 4+ weeks).
Bleaching occurs when the zooxanthellae become severely damaged from some sort of stressor. In natural situations this stress usually results from severe oxidative stress, that is, when reactive oxygen species are produced in the chloroplasts of the zooxanthellae and start oxidizing (= destroying) everything they come in contact with. The ROS that cause that stress can directly and signifcantly damage the coral tissues, which is one reason corals bleach when their zoox. get really monkied up. There are a variety of mechanisms that can lead to that oxidative stress.
For example, when corals undergo photobleaching (from a sudden increase in light intensity) they end up collecting far more photons than they can use in photochemistry. Hence, they have a lot of excited (= high energy) electrons that are not quenched photochemically. Photosynthetic organisms have means of quenching some of those electrons via the xanthophyll cycle (termed "nonphotochemical quenching), thereby preventing the production of ROS by those electrons. Some of that energy will also be quenched via fluorescence.
While the process of e- transport down the e- transport chain is very efficient, some e- always end up getting "lost" down the path. Due to the high concentration of O2 in the area, that makes it conducive for the production of ROS. When we have high light relative to what the organism is adapted to we have more electrons that are NOT quenched photochemically and the potential for more of them to get "lost", leading to more ROS produced and making for badness.
When zooxanthellae experience temperature stress (or other organisms too) the lipids that make up the thylakoid membrane become more fluid. Think about butter in the refrigerator vs. room temperature vs. in the oven. As the temperature increases the membranes begin to melt. For the e- transport chain to work the proteins have to be spatially arranged in a very precise configuration. As the thylakoid membrane becomes more fluid (= melts) the proteins imbedded in it end up in incorrect configurations. Hence, more and more of those excited electrons get lost, create ROS, and badness ensues. A friend of mine actually studied this aspect of bleaching physiology for her MS thesis and got incredibly interesting results.
Increased UV, some viruses, some sfungal infection, some herbicides, etc. can also produce more ROS in plants via a several known pathways.
Hence, while the mechanism that leads to ROS production varies in, for example, high light stress vs. temperature stress, the result is effectively the same. To the zooxanthellae in a coral, temperature stress effectively "feels" like high light stress (although elevated temperature can and does harm other processes as well).
Agreed about the heat produced via non-photochemical quenching as being inconsequential in any normal circumstance. There simply isn't enough energy lost through this mechanism to heat the coral appreciably. Along these lines, however, some people have in fact measured temperature differences in dark colored vs. light colored corals in nature. The dark corals absorb more visible and IR radiation and have been measured at up to a couple of degrees C above ambient in nature in relatively stagnant water flow. However, that only becomes important when ambient temperatures are at or above normal thermal limits (for most corals in nature those limits are temperatures sustained in the range of ~86-95 F for 4+ weeks).
ReefEnabler
Premium Member
Very interesting thread, there's alot to digest here.
I am really interested what you guys think of Dana Riddle article on Lamp spectrum from 5k -20k
http://www.advancedaquarist.com/2008/12/aafeature1
I've asked about it in a few other threads but nobody has much response.
His findings seem odd and backwards to what I expected based on the assumption that lower kelvin is a more efficient conversion from watts to PAR since it takes less energy to emit photons with slower wavelength.
He noticed increased growth with increased color temperature (although the 10k beat the 5k, obviously the color temp is not an end all but just an arbitrary manufacture label).
Of note, this is the first article I've actually seen use PUR as a measure instead of PAR. And also the first article I've seen claim that "Bluer" bulbs can grow certain corals quicker DESPITE the lower efficiency of the electronics involved.
Also, the note on red lighting causing severe bleaching was interesting.
It sounds like in this experiment, the coral was provided with ONLY red light, versus supplementing with a red light.
Alot of RCers have added the ATI procolor bulb to their T5 mix which is a bulb with a good red spike. I am thinking of doing this also but want to get your thoughts. There is even mention in this thead that a supplemental red spectrum could help corals achieve better color.
I currently have
MH:
2x250w 14k hamilton
1x400w 20k radium (center of tank)
VHO: 2 x 140w UVL Super Actinic
T5: 2 x 80w ATI Blue Plus
So my tank is VERY skewed in the blue spectrum, probably lacking in the red compared to shallow reef depths in nature even.
I only added the T5s about 8 weeks ago and my red and green Montis have started turning more pastel. They have the same color intensity but are simply lighter. But it could just as easily also be that my system has very low nutrient levels even though I feed heavily for anthias.
I am thinking of replacing one of the VHO Actinics with a T5 ATI Procolor bulb to balance the spectrum a little bit, in hopes it will help regain some of the color.
wow sorry long post thanks if you made it this far :lol:
I am really interested what you guys think of Dana Riddle article on Lamp spectrum from 5k -20k
http://www.advancedaquarist.com/2008/12/aafeature1
I've asked about it in a few other threads but nobody has much response.
His findings seem odd and backwards to what I expected based on the assumption that lower kelvin is a more efficient conversion from watts to PAR since it takes less energy to emit photons with slower wavelength.
He noticed increased growth with increased color temperature (although the 10k beat the 5k, obviously the color temp is not an end all but just an arbitrary manufacture label).
Of note, this is the first article I've actually seen use PUR as a measure instead of PAR. And also the first article I've seen claim that "Bluer" bulbs can grow certain corals quicker DESPITE the lower efficiency of the electronics involved.
Also, the note on red lighting causing severe bleaching was interesting.
It sounds like in this experiment, the coral was provided with ONLY red light, versus supplementing with a red light.
Alot of RCers have added the ATI procolor bulb to their T5 mix which is a bulb with a good red spike. I am thinking of doing this also but want to get your thoughts. There is even mention in this thead that a supplemental red spectrum could help corals achieve better color.
I currently have
MH:
2x250w 14k hamilton
1x400w 20k radium (center of tank)
VHO: 2 x 140w UVL Super Actinic
T5: 2 x 80w ATI Blue Plus
So my tank is VERY skewed in the blue spectrum, probably lacking in the red compared to shallow reef depths in nature even.
I only added the T5s about 8 weeks ago and my red and green Montis have started turning more pastel. They have the same color intensity but are simply lighter. But it could just as easily also be that my system has very low nutrient levels even though I feed heavily for anthias.
I am thinking of replacing one of the VHO Actinics with a T5 ATI Procolor bulb to balance the spectrum a little bit, in hopes it will help regain some of the color.
wow sorry long post
thanks if you made it this far :lol:
DheereCrossing
New member
I would imagine that zooanthelae aren't used to receiving much red spectrum photons and are simply trying to adapt or create new cells that can more readily capture these photons. Just a guess though.
MCsaxmaster
New member
I read Dana's article with great interest. He very appropriately is cautious in drawing sweeping conclusions from Schlacher et al., 2007 that he sites. Dana's article definitely sparked my interest though, so I went to the Schlacher et al., 2007 article. Having read that, I think there are some serious and significant methodological issues with the study. They *might* be onto something, but based on what they did in the paper...well, I wouldn't take the data as representative 
Having said that, I think Dana might be onto something, or at the very least I think his ideas are worth further development. Significant amounts of red light isn't something corals in all but the shallowest water would be exposed to. Only additional study will resolve this issue though.
Having said that, I think Dana might be onto something, or at the very least I think his ideas are worth further development. Significant amounts of red light isn't something corals in all but the shallowest water would be exposed to. Only additional study will resolve this issue though.
