Advanced Topic Too Much Light Bleaching Corals

Discussion in 'Advanced Topics' started by Midnight Reefer, 15 Feb 2014.

  1. Midnight Reefer

    Midnight Reefer

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    Hi All

    I have been doing the whole science thing and reading papers on coral bleaching and an interesting explanation comes up for why SPS corals bleach due to too much light.

    Photosynthesis occurring inside the coral produces oxygen. O2, Ok, awesome

    The coral cannot stop the zooxanthellae it hosts from photosynthesising and producing said oxygen.

    Now the chemistry comes in; water is obviously H2O and coral polyps have some water in them....duh.....

    So the algae produces excess oxygen which cannot be 'processed' by the coral for whatever reason. So.....The following reaction is said to happen;

    2(H2O) + O2 <---> 2(H2O2)

    H2O2 is peroxide, the 2's are subscript.

    Coral does what it can to stop the source of the excess oxygen and survive. Goodbye zooxanthellae.

    Hope this this makes you scratch your head :)
     
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  3. irie ivan

    irie ivan MASA Contributor

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    Not that i had an itch to scratch...
    But why can the coral not use or get rid of excess oxygen or the peroxides?

    Photosynthtic saturation... And how soon it is reaches the point is relative...
    Peroxidases... Enzyme complex used to process...
    And their ability to deal with oxygen radicals... Interesting
    Flow dynamics, acting as a heat exchange point.
    temperature.... All a role to play.

    Why is this in the beginner section?

    PLOS ONE: Oxygen and Heterotrophy Affect Calcification of the Scleractinian Coral Galaxea fascicularis

    http://jeb.biologists.org/content/214/9/1533.full.pdf
     
    Last edited: 15 Feb 2014
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  4. Midnight Reefer

    Midnight Reefer Thread Starter

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    @irie ivan
    Thanks for the input, in the beginner section because its not really that important but beginners might remember why to be careful with lighting and I don't want to overload anyone with information :)

    Everything has a little role in the de-gassing of oxygen of light dependant coral in my opinion, but I'm not a marine biologist or a zoologist. The peroxide is not stable as I understand it and breaks down naturally very fast and some corals are better adapted than others to deal with the oxygen load with enzymes etc.

    It also is the reason why DO(dissolved oxygen) is measured in very sensitive aquariums or with ozone use, DO above 100% is not a good thing!! Between 80% and 90% is ideal.

    Some papers even suggest the GFP(green fluorescent pigment) in the fluorescent green corals is actually a 'sun-block' for coral against UV rays. Motivation being that the light and colours our eyes see, is the light being reflected off the coral.

    Flow, temperature, water quality, 'nutrient' levels and gas exchange rates are definitely factors that need to be taken into consideration, especially with SPS coral which cannot change shape or size to change their exposure to the sun or flow.

    But I guess the ultimate conclusion I feel I'm trying to get at is that; its not one factor, or two factors, or even 3 factors that cause coral to bleach from too much light or oxygen over saturation in the wild. It's a combination of EVERYTHING changing too quickly for corals to adapt.

    In our aquariums though, It's pretty damn obvious when a coral has bleached because of too much light, especially with all this LED witchcraft!!


    But I found out yesterday, xenia can be farmed under a 24/7 lighting! Now that really stirs the conversation
     
    Last edited by a moderator: 26 Nov 2015
  5. RiaanP

    RiaanP Moderator

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    H2O2
    There you go...
     
  6. carlosdeandrade

    carlosdeandrade

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    Increase laminar flow around coral so that it can have greater gaseous exchange as per Jake Adams research on flow and gaseous exchange linked to lighting. Some of our members were fortunate enough to see that talk/ @dallasg, @butcherman, @Nemos Janitor, @Hails, @GTH
     
    Last edited by a moderator: 26 Nov 2015
  7. butcherman

    butcherman Moderator MASA Contributor

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    how would we define to much light. Are we talking intensity or photo period, or both?
     
  8. butcherman

    butcherman Moderator MASA Contributor

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    Carlos is correct here the more flow around a coral the more gasses are exchanged here.
    Jake likened a corals breathing to a person standing on a hill with his lungs outside his body, hoping the wind would be enough for him to breath.
     
  9. Nemos Janitor

    Nemos Janitor

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    I am going to ask what is light?

    Light without UV?? will that cause bleaching because the zoo have nothing to protect?

    Can the manipulation of UV frequencies change coral coloration?
     
  10. butcherman

    butcherman Moderator MASA Contributor

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    Good questions with led's our spectrums have become so narrow are we providing everything?

    with out UV your corals will not colour up will they?

    Only if your nutrients are low. Ie no food for the zooxanthellae ;)
     
  11. viper357

    viper357 Admin MASA Contributor

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  12. Midnight Reefer

    Midnight Reefer Thread Starter

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    Whoa, thanks for the input guys. You all have it spot on and thankyou for the furthur reading.

    I guess when we talk about light, the sun is everything, UV-a b and c, the whole spectrum with odds and ends. No special UV shielding. In our aquariums, the lighting is pretty darn unnatural compared to the sun all day long. This is not a bad thing as we know what light wavelengths corals thrive under and LED's are technologically capable of replicating wavelengths. But......

    In the aquarium setting, what I have seen the most; is reefkeepers accidentally leaving their lighting on for 2 hours or so after the established photoperiod. Making some coral, such as a doughnut LPS, expel the zooxathellae as little bundle of brown tubes. I have seen this with my own eyes. And of course, the usual case, upgrading to stronger lighting that is too strong :)

    Then the coral is bleached but it is not yet dead. I'm not sure how this photoperiod change would happen in the wild but cloudy days or storms happen on reefs. But don't cause mass bleaching I don't think. Perhaps with global warming and these events becomming more extreme, they could possibly play a role.

    As I mentioned, I feel confident it is a combination of stressors that lead to the demise of actual reefs with respect to global warming. blaming or focussing on a single factor is a bit simplistic I feel to interpret mass bleaching.

    We hear that some members systems run at 30 degrees in the summer which coral tolerates if it gradually is given chance to adapt appropriately, the same with acclimating for photoperiods. It's all not too sudden to overwhelm the coral with its algae going nuts.

    Flow is definitely a massive factor as this transports and chemically homogenises the environment around a coral, but if the DO for example is too high in the aquarium or environment to establish a significant gradient between the coral and the water it's kept in. You can blow the coral away with flow but won't do any good as oxygen cannot diffuse effectively enough for survival.

    Example of one factor affecting another directly. Now temperature and the rest into the equation........Not a simple discussion.

    But the colours which SPS adopt sparks an interesting adaption. The colour we see is the colour of the light reflected from objects.

    Therefore the colours developed with respect to the light the coral is kept under, could be the coral adapting and focussing on the wavelengths it prefers and reflecting those it doesn't. A theory anyways. The nutrients or whatever potentially just enabling the coral to adapt, giving it 'fuel' as it were.

    People always say; ''Çorals are sensitive' which I can agree, they are fairly sensitive but on the other hand, also tough as some can adapt to drastic changes in environment given enough time. changing a a photoperiod of a 1.2m SPS tank by 2 hours under a 400W halide is not enough time lol
     
  13. Midnight Reefer

    Midnight Reefer Thread Starter

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    Ah, also to note, some UV rays are proven as photosynthetic inhibitors, so corals in the wild need to overcome this problem, which they do!
     
  14. carlosdeandrade

    carlosdeandrade

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    Producing photochromic chemicals which protect them from "sunburn." That's why we have different colours in corals.
     
  15. Nemos Janitor

    Nemos Janitor

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  16. viper357

    viper357 Admin MASA Contributor

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  17. Nemos Janitor

    Nemos Janitor

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    Did you understand it? :p not sure I did.:blush:
     
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