futrtrubl
New member
Yes heat is the big one and you'll probably never see bleaching because of one of the other factors, but together with heat or other factors these can be the difference between recovery and death. Besides, heat as a cause has been dealt with by others.
A researcher came down recently to do a study on a possible mechanism for bleaching and the role of light. After seeing the results I asked if I could post them to this forum, he enthusiastically said yes and gave me a paper/poster I could post for all to see. download 159kb
In summary the proposed mechanism is that zooxanthellae produce hydrogen peroxide as a normal part of photosynthesis and the rate increases with increasing light levels. This hydrogen peroxide interferes with a calcium exclusion pump in cells and an increased Ca+ concentration in the cells causes the expulsion of the algae. Heat also interferes with the pump so in the presence of light the pump can break down at lower temperatures.
What does this mean for aquarists? I know most people turn off their lights to control their water temperatures if it rises too much, Ubut this shows that it is doubly imperative to turn lights down or off if temperatures start to rise. By my estimation turning off the lights can give you an extra ~3C/5.5F head room (~33C in light to 36C in the dark for complete fragmentation in 2 hours. These raw temperatures are valid only for his experiment and shouldn’t be used for your aquarium, different coral/zooxanthellae combinations have different tolerances) on your water temperature as well as help control your water temperature.
But what about the other factors he lists; cold shock, increased UV, vibrios, reduced salinity and oxygen stress?
Cold Shock: I wasn’t able to find an abstract for Muscatine et al’s paper, but what I get from those that cited him is that if the coral is exposed to colder water then returned to the original or higher temperature in a short period the coral may bleach. I don’t know what temperature regimen we are looking at here but watch out for this with any emergency cooling measures you take (iced bottles, transfer to a cooled container etc).
Increased UV: I think many know about this already, but it’s worth stating. Fix those UV lenses!
Vibrios: No worries, your corals are safe from the sound of your pumps. Vibrios are a group of rod shaped bacteria which includes cholera. Kushmaro et al found that all and only bleached areas of a certain coral were infected with a certain bacteria and when healthy corals were injected with the bacterium they became bleached. Don’t really have a recommendation here, though a UV sterilizer may help.
Reduced Salinity: I very much doubt anyone will dump uncontained ice in their tanks to drop temperatures, but this is something to think about if when it comes to hyposaline treatments. Not sure how reduced it has to be for effects.
Oxygen Stress: We’re coming back to the peroxide thing again. But things that can create “reduced oxygen intermediates†(superoxide, peroxide, or the hydroxyl radical) may warrant some attention. I’ve never looked into getting an ozone system so I don’t know if there is a tolerance for some or no ozone in the tank itself though I do know that ROIs (my own acronym, gotta have one ;’] ) are quickly reduced to harmless forms in water. Also UV can produce free radicals but again, they may not persist long enough. But there is good news! I just saved… ehem… peroxide only becomes harmful if it builds up in the coral faster than it can be gotten rid of, which it can do through too methods. First it has a suite of enzymes designed to reduce peroxide harmlessly. The second is the simple diffusion of the peroxide out of the polyp. This can be increased with increased water flow over the coral.
Help! My corals are bleaching/may bleach! What can I do?
- First off, you probably need to get those temps back down (it is the most common reason after all) just step away from the fire extinguisher and ice tray (unless you plan to contain it).
- If your temps are fine check your lights for UV shield problems.
- For extra insurance or if you think things are bad enough turn off/down those lights.
- If your corals can take it you can increase water flow over them to take away the peroxide.
- If you are a natural sea water kind of guy (I am) you may want keep off the stuff for a while as it may introduce vibrios (they are exclusively aquatic and many are salt loving).
- I don’t really think I have enough evidence to recommend turning off ozone systems.
- If your corals have bleached you may notice them extend feeding tentacles at times they normally don’t. This is because they have lost a food source, the primary one for many hermatypic (reef building) corals, so one of the things you can do for them is step up any feeding regime you have for them. In the wild some corals can recover after being bleached for 2 months, probably due to filter feeding.
FITT, W.K. & M.E. WARNER (1995).
Patterns of bleaching of four species of Caribbean corals. Biological Bulletin,189: 298-307. download 896kb
Goreau, Thomas F. (1964)
Mass Expulsion of Zooxanthellae from Jamaican Reef Communities after Hurricane Flora. Science, 145(3630):383-386 abstract
Jokiel, P. L. (1979)
Solar Ultraviolet Radiation and Coral Reef Epifauna. Science, 207:1069
Kushmaro, A; Loya, Y; Fine, M; Rosenberg, E (1996)
Bacterial infection and coral bleaching. Nature, 380(6573):396 abstract
Lesser, M. P. (1997)
Oxidative stress causes coral bleaching during exposure to elevated temperatures. Coral Reefs, 16(3):187-192 abstract
Muscatine, L., D. Grossman, and J. Doino (1991)
Release of symbiotic algae by tropical sea anemones and corals after cold shock. Marine Ecology Progress Series, 77: 233-243.
SANDEMAN, I. (2006)
What Happens When Corals Bleach: A New Perspective. Download 159kb
Edward
A researcher came down recently to do a study on a possible mechanism for bleaching and the role of light. After seeing the results I asked if I could post them to this forum, he enthusiastically said yes and gave me a paper/poster I could post for all to see. download 159kb
In summary the proposed mechanism is that zooxanthellae produce hydrogen peroxide as a normal part of photosynthesis and the rate increases with increasing light levels. This hydrogen peroxide interferes with a calcium exclusion pump in cells and an increased Ca+ concentration in the cells causes the expulsion of the algae. Heat also interferes with the pump so in the presence of light the pump can break down at lower temperatures.
What does this mean for aquarists? I know most people turn off their lights to control their water temperatures if it rises too much, Ubut this shows that it is doubly imperative to turn lights down or off if temperatures start to rise. By my estimation turning off the lights can give you an extra ~3C/5.5F head room (~33C in light to 36C in the dark for complete fragmentation in 2 hours. These raw temperatures are valid only for his experiment and shouldn’t be used for your aquarium, different coral/zooxanthellae combinations have different tolerances) on your water temperature as well as help control your water temperature.
But what about the other factors he lists; cold shock, increased UV, vibrios, reduced salinity and oxygen stress?
Cold Shock: I wasn’t able to find an abstract for Muscatine et al’s paper, but what I get from those that cited him is that if the coral is exposed to colder water then returned to the original or higher temperature in a short period the coral may bleach. I don’t know what temperature regimen we are looking at here but watch out for this with any emergency cooling measures you take (iced bottles, transfer to a cooled container etc).
Increased UV: I think many know about this already, but it’s worth stating. Fix those UV lenses!
Vibrios: No worries, your corals are safe from the sound of your pumps. Vibrios are a group of rod shaped bacteria which includes cholera. Kushmaro et al found that all and only bleached areas of a certain coral were infected with a certain bacteria and when healthy corals were injected with the bacterium they became bleached. Don’t really have a recommendation here, though a UV sterilizer may help.
Reduced Salinity: I very much doubt anyone will dump uncontained ice in their tanks to drop temperatures, but this is something to think about if when it comes to hyposaline treatments. Not sure how reduced it has to be for effects.
Oxygen Stress: We’re coming back to the peroxide thing again. But things that can create “reduced oxygen intermediates†(superoxide, peroxide, or the hydroxyl radical) may warrant some attention. I’ve never looked into getting an ozone system so I don’t know if there is a tolerance for some or no ozone in the tank itself though I do know that ROIs (my own acronym, gotta have one ;’] ) are quickly reduced to harmless forms in water. Also UV can produce free radicals but again, they may not persist long enough. But there is good news! I just saved… ehem… peroxide only becomes harmful if it builds up in the coral faster than it can be gotten rid of, which it can do through too methods. First it has a suite of enzymes designed to reduce peroxide harmlessly. The second is the simple diffusion of the peroxide out of the polyp. This can be increased with increased water flow over the coral.
Help! My corals are bleaching/may bleach! What can I do?
- First off, you probably need to get those temps back down (it is the most common reason after all) just step away from the fire extinguisher and ice tray (unless you plan to contain it).
- If your temps are fine check your lights for UV shield problems.
- For extra insurance or if you think things are bad enough turn off/down those lights.
- If your corals can take it you can increase water flow over them to take away the peroxide.
- If you are a natural sea water kind of guy (I am) you may want keep off the stuff for a while as it may introduce vibrios (they are exclusively aquatic and many are salt loving).
- I don’t really think I have enough evidence to recommend turning off ozone systems.
- If your corals have bleached you may notice them extend feeding tentacles at times they normally don’t. This is because they have lost a food source, the primary one for many hermatypic (reef building) corals, so one of the things you can do for them is step up any feeding regime you have for them. In the wild some corals can recover after being bleached for 2 months, probably due to filter feeding.
FITT, W.K. & M.E. WARNER (1995).
Patterns of bleaching of four species of Caribbean corals. Biological Bulletin,189: 298-307. download 896kb
Goreau, Thomas F. (1964)
Mass Expulsion of Zooxanthellae from Jamaican Reef Communities after Hurricane Flora. Science, 145(3630):383-386 abstract
Jokiel, P. L. (1979)
Solar Ultraviolet Radiation and Coral Reef Epifauna. Science, 207:1069
Kushmaro, A; Loya, Y; Fine, M; Rosenberg, E (1996)
Bacterial infection and coral bleaching. Nature, 380(6573):396 abstract
Lesser, M. P. (1997)
Oxidative stress causes coral bleaching during exposure to elevated temperatures. Coral Reefs, 16(3):187-192 abstract
Muscatine, L., D. Grossman, and J. Doino (1991)
Release of symbiotic algae by tropical sea anemones and corals after cold shock. Marine Ecology Progress Series, 77: 233-243.
SANDEMAN, I. (2006)
What Happens When Corals Bleach: A New Perspective. Download 159kb
Edward