LEDs and PAR/Quantum Meters Part 2: PAR

[GeorgeMonnatJr]

This is the middle part of my experiences so far with reef aquarium lighting continuing from my general thoughts on technologies (Part 1) with the end goal of how I measured my LEDs (Part 3).

As before, this blog is as much a place for me to keep my thoughts straight and engender discussion and something to refer to instead of retyping the same material a lot as it is a place to share information.

I'm not even close to being an expert on reef tanks, yet (maybe in a couple of decades), and I'm not a biologist or botanist. If you are an expert and you see something factually wrong please let me know, and I'll correct it. (Comments on my grammar and citation style will probably be ignored )

I do know LEDs and silicon-based photometers/photo-sensors (my title at work is Optoelectronic Engineer). I find myself re-posting the same graphs and explanations, so I figured I'd put it all in a blog that I can refer people to as needed. You can skip to Part 3: Quantum Sensors and LEDs if the background info is too boring.


Photosynthetically Useful Radiation (PAR)

So I wasn't interested in LEDs initially - until I learned about PAR (Photosynthetically Useful Radiation). I saw graphs for chlorophyll spectrum used in numerous places, like this one [5].

The first thing I noticed from the graphs is that very little of the green and yellow portion of the spectrum is used. That started me leaning towards LEDs, because they are ideal for hitting peaks and not emitting in "dead zones" like on the previous graph. The areas where chlorophyll doesn't use light, mainly 475nm to 625nm or green to orange, is used by things we don't want growing in our tanks. "Cyanobacteria and red algae have phycocyanin and allophycocyanin as accessory pigments to absorbe orange light. They also have a red pigment called phycoerythrin that absorbs green light and extends the range of photosynthesis [6]."

Apparently chlorophyll c is a bad thing as only unwanted pests like algae, cyanobacteria (cyano) and dinoflagellates (dinos) use it. "A third form of chlorophyll which is common is (not surprisingly) called chlorophyll "c", and is found only in the photosynthetic members of the Chromista as well as the dinoflagellates [7]." Apparently another concern is fucoxanthin, "the brown pigment which colors kelps and other brown algae as well as the diatoms [7]."

I hadn't found an absorption spectra graph for chlorophyll c (to avoid those frequencies/wavelengths), but then I stumbled on an awesome chart [8]. It shows chlorophyll c (pale red trace) in the bottom, middle graph with a peak to the right of chlorophyll a (black trace). It looks very close to chlorophyll b, so I'm guessing I can't filter it out. The chart also clearly shows that fucoxanthin used by algae and diatoms is in the green range and algae in general needs the green to orange light for photosynthesis, including phycoerythrin and phycocyanin.

Here's a question for you expert reefers: Do coral use phycoerythrin and phycocyanin or another chlorophyll accessory pigment? (feel free to post below) Phycocyanin especially seems useless to species living deeper than a few meters, so I'm guessing no. If not, then eliminating the green, yellow and orange light will help eliminate cyano and nuisance algae, because they do depend on those proteins, right?

Eliminating those colors, or wavelengths, means uglier coral that looks more bland - like most of my crappy dive photos with my cheap, little flash.

Just to see more than one source, here's another chart [9].

I don't want to go deeper into photosynthesis, because it's not my field. From what I've seen, I prefer lots of blue light (400nm-480nm). Some red (640nm-680nm) may also be useful, but species that live deeper than about 3m/10ft never see red anyway. Surface species like floating algae are more apt to use the red light to grow, which I don't want. The stuff I don't like uses the green to orange (480nm-640nm) light, so I only want just enough green/yellow/orange/red for color rendering to make my livestock look pretty to the human eye while maintaining healthy coral, anemones and clams.

After all that, I finally get to the purpose of this whole blog. How I use an affordable quantum sensor to more accurately measure the PAR of my reef aquarium LED fixtures.


Part 1: Technologies

Part 3: Quantum Sensors and LEDs

References

[5] Light In Lakes, 01MAY2012

[6] Hyperphysics, Pigments for Photosynthesis, 01MAY2012

[7] University of California Museum of Paleontology, Photosynthetic Pigments, 01MAY2012

[8] ATJ's Marine Aquarium Site, Photosynthesis, 01MAY2012

[9] Steve Berg, Winona State University, Chapter 15: Photosynthesis, 02MAY2012

 

[GeorgeMonnatJr]

I just stumbled on a great resource. This pdf describes in greater detail that's easy to understand the stuff I mentioned above.

Emmanuel Boss (Guest Lecturer), The University of Maine: School of Marine Sciences: Maine In-situ Sound & Color (MISC) Lab, Light and biology in the ocean, posted 2006, 03MAY2012

I was looking for normal PAR readings of the sun when I found it. I'll try to work it into my blog above, but I think I'm at or near the character limit.

 

[GeorgeMonnatJr]

Cyanobacteria Action Spectra

I was researching cyanobacteria (cyano) and how to get rid of it after reading complaints, and I came across a great reference. I wish I wasn't at a character limit in the blog, but in the future I may rewrite it with this reference.

Photosynthesis: Light energy transduced to chemical energy, Pigments and absorption spectra, updated 11/30/2008, 09MAY2012

Phycobilins are water-soluble pigments, so they are found in the cytoplasm, or in the stroma of the chloroplast. Phycolibins occur in Cyanobacteria (phycocyanin and phycoerythrin) and the "red algae", the Rhodophyta (phycoerythrin).

My conclusion from this is that cyano MUST have green-to-orange light (480nm - 640nm) to derive significant energy from photosynthesis. That is why old MH and florescent bulbs can cause cyano outbreaks - they have more green-to-orange light. Blue LEDs have none of that and "white" LEDs have less than MH.

My question above still stands, does anyone know if corals need the green-to-orange light (480nm - 640nm)? If not, then with LEDs it should be very simple to starve out the cyano while still feeding coral. For comparative spectra of MH and LEDs, see Part 1 of my blog.

 

[GeorgeMonnatJr]

F. favus Zooxanthellae Action Spectra

In an attempt to answer my own questions above about coral spectra requirements, I found this reference.

O. Levy*, Z. Dubinsky and Y. Achituv, The Journal of Experimental Biology, Photobehavior of stony corals: responses to light spectra and intensity, Accepted July 22, 2003, 09MAY2012

Absorption characteristics of the major pigments extracted from F. favus zooxanthellae. Pigments are: Chl, chlorophyll; Chld, chlorophyllidae; Per, perdinin; Dia, diatoxanthin; Dino, diadinoxanthin.

That chart and the one in my previous comment tell me you could use LEDs to provide light from about 430nm to 500nm but no light from 500nm to 650nm and effectively starve out the cyano without harming the coral. Or at least that would work for one kind of head coral.

I'd still like a marine biologist/botanist to back me up - or even to refute what I'm saying.

 

[Timfish]

Another interesting datum is in some cases the red fluorescing some corals show is not done by pigments the coral produces or are produced by the zooxanthellae but by symbiotic cynobacteria with in the host cells.

Delbeeck & Sprung "The Reef Aquarium" Vol III, pg 515

 

[GeorgeMonnatJr]

George, you are aware the zooxanthellae species are dinoflagellates in the genus Symbiodinium? Unless it can be specifically shown this genus does not use it this would seem to me to make chlorophyll C important for the survival of corals.

Delbeck & Sprung, "The Marine Aquarium" Vol I pg 47 &
http://en.wikipedia.org/wiki/Symbiodinium

No, I'm admittedly ignorant of how corals "work". That's why I'm fascinated by and really appreciate any comments like yours by people who know better. I need to get all of the Sprung books (saw one at Half Price Books for $45, looked online and saw cheapest was around $200 on Amazon, went back to Half Price and it was gone. Did you snag it? )

What I really need is a list of which coral groups use which zooxanthellae species and their specific action spectra. I'm fairly confident in saying that the deeper the ecological niche that a coral species inhabits, the less green-to-red light it needs to grow.

 

[GeorgeMonnatJr]

Another interesting datum is in some cases the red fluorescing some corals show is not done by pigments the coral produces or are produced by the zooxanthellae but by symbiotic cynobacteria with in the host cells.

Delbeeck & Sprung "The Reef Aquarium" Vol III, pg 515

Everything about coral and marine biology is still fascinating to me, so thank you for the comments.

 

[Timfish]

. . . I need to get all of the Sprung books (saw one at Half Price Books for $45, looked online and saw cheapest was around $200 on Amazon, went back to Half Price and it was gone. Did you snag it? )
. . . a list of which coral groups use which zooxanthellae species and their specific action spectra. . . .

No. I heard Delbeek & Sprungs books were going out of print but I was blown away by the prices on Amazon.

Search Dana Riddle and Sanjay Joshi for more on fluorescing pigments, lighting and coral but there are certainly other researchers. Corals pick zooxanthellae partly on environmental cues so I doubt there's a strict correlation between coral and zooxanthellae sp.