UV vs Near UV Question

silverwolf72 · 08/27/2010, 01:01 PM

I keep reading that corals don't receive UV because the water blocks most of it.
But blue light travels the deepest in water, how is it that 300nm gets blocked but 400nm doesn't?

T Diddy · 08/27/2010, 08:40 PM

Quote:

Originally Posted by silverwolf72

I keep reading that corals don't receive UV because the water blocks most of it.
But blue light travels the deepest in water, how is it that 300nm gets blocked but 400nm doesn't?

It doesn't...that's in part what zooxanthellae are for. Rest assured that if coral recieves any visible light in the wild, it is also recieving UV.

reefgeezer · 08/27/2010, 09:34 PM

If I understand correctly corals use UV-A, violet, blue, and red light for photosynteisis (sp?). UV penitrates water deeper than higher frequency visible light. I can't cite papers, but I believe corals that evolved in shallow waters use a greater proportion of higher frequency light like blue and even red. Corals that evolved in deeper waters use a greater proportion of low frequency light like UVA and violet to blue.

silverwolf72 · 08/27/2010, 10:29 PM

Then I'm totally lost why I keep seeing post about needing to block all UV and any thing below 405nm will cause your corals to bleach

reefgeezer · 08/27/2010, 11:45 PM

I think the blocking UV light is in reference to halide lighting which can generate some pretty intense UV, much more intense that natural sunlight. As far as light below the visible light spectrum, 400 nm or so, as far as I know there is no mechinism in water to block it. Corals have developed defenses just like we have. Additionally, across the UV spectrum, the higher frequency (UV-B I think) is not as harmful as the lower frequencies. I believe the higher end of the UV spectrum is used by corals.

08/27/2010, 01:01 PM	#1
silverwolf72 Registered Member Join Date: Jul 2005 Location: Lake Forrest CA Posts: 1,732	UV vs Near UV Question I keep reading that corals don't receive UV because the water blocks most of it. But blue light travels the deepest in water, how is it that 300nm gets blocked but 400nm doesn't?

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08/27/2010, 09:34 PM	#3
reefgeezer Registered Member Join Date: Dec 2009 Location: Wichita KS Posts: 2,621	If I understand correctly corals use UV-A, violet, blue, and red light for photosynteisis (sp?). UV penitrates water deeper than higher frequency visible light. I can't cite papers, but I believe corals that evolved in shallow waters use a greater proportion of higher frequency light like blue and even red. Corals that evolved in deeper waters use a greater proportion of low frequency light like UVA and violet to blue.

08/27/2010, 10:29 PM	#4
silverwolf72 Registered Member Join Date: Jul 2005 Location: Lake Forrest CA Posts: 1,732	Then I'm totally lost why I keep seeing post about needing to block all UV and any thing below 405nm will cause your corals to bleach

08/27/2010, 11:45 PM	#5
reefgeezer Registered Member Join Date: Dec 2009 Location: Wichita KS Posts: 2,621	I think the blocking UV light is in reference to halide lighting which can generate some pretty intense UV, much more intense that natural sunlight. As far as light below the visible light spectrum, 400 nm or so, as far as I know there is no mechinism in water to block it. Corals have developed defenses just like we have. Additionally, across the UV spectrum, the higher frequency (UV-B I think) is not as harmful as the lower frequencies. I believe the higher end of the UV spectrum is used by corals.