Peer Reviewed White Papers on PAR/Coral Growth?

[webersp]

TL;DR - I’m wondering if anyone can share any white papers or other peer reviewed scientific publishings showing a strong correlation between PAR levels and coral growth. 
 

Context: I haven’t been “hip” to the hobby in awhile, but I’ve consistently maintained a tank and I’m using the same Kessil A160 I’ve had for 6+ years; before that I had some A150s, halides, T5s, some Steve’s/Rapid LED DIYs, and some old far eastern box LEDs.
Started poking around the saltwater forums recently (not just nano-reef) and seeing what’s new, and I’m noting that, in terms of lighting, there seems to be heavy focus on;

A. Getting VERY high PAR numbers for SPS

B. Properly acclimating them to not bleach under those ratings

C. Using LEDs that are already powerful enough to bleach coral, and then supplementing them with T5s.  
 

I can’t find any (legitimate) readily available data on the correlation between growth and PAR - when Kessil A150s were new (many moons ago), there was constant talk about how to acclimate new inhabitants to prevent bleaching - now just about every thread about even the A160 insists that they’re only good for a few softies and LPS in the smallest nano tanks.  It’s a single anecdotal example, but that’s when I first started to notice people having to turn their lights down to keep coral happy - black boxes were the same way. 
 

Is this some sort of PAR “arms race” spurred by the early SMD LEDs that were neither the correct power or spectrum? Are people

ill-advisedly chasing higher PAR numbers when what they really want is the spectrum and consistent shading of T5s, but without the inconvenience of bulbs? The last time I got rid of a T5 fixture, I couldn’t pay someone to take it off my hands. It seems they’re headed the way of vinyl and becoming “retro” cool/functional as people get back to basics. But all of this is making me wonder, does coral actually benefit from excessive PAR?
 

 

[mcarroll]

On 9/14/2023 at 12:19 AM, webersp said:

there seems to be heavy focus on;

A. Getting VERY high PAR numbers for SPS

B. Properly acclimating them to not bleach under those ratings

C. Using LEDs that are already powerful enough to bleach coral, and then supplementing them with T5s.  

Your observations are not incorrect. 😉 

On 9/14/2023 at 12:19 AM, webersp said:

I can’t find any (legitimate) readily available data on the correlation between growth and PAR[....]
[....]all of this is making me wonder, does coral actually benefit from excessive PAR?

First, without referring to non-hobby sources, lighting is one area we have had good "in house" research.  (Chemistry is the other main area.)  

 

Among other sources, Dana Riddle in particular, laid out the case that we are (or were, for those paying attention) over-lighting their corals, sometimes by a WIDE margin.  

 

His articles were mostly in the now-defunct advancedaquarist.com website....which is now technically a part of reefs.com, as their "Reefs Magazine"...but older articles (from the old website) are still not indexed, so require some digging to find.  The best article I could find with a few minutes digging through their "feed" was "Lighting for Reef Aquaria: Tips on Taking Light Measurements" which, which very good reading, only addresses recommended light levels in summary fashion in the paragraph on "Coral Light Requirements"....in part...

 

Quote

Although we generally think of corals as originating from brightly lighted natural reefs and naturally assume corals need lots of light, the truth is that most corals require relatively little in order to thrive.[....]

That article also has a nice summary of converting from lux to PAR measurements.  If you can find his other articles on lighting, they elaborate greatly on the "why's"?  

 

Regarding coral requirements, I found similar info in an old journal article (can't recall exactly where this detail was, but it's one of the articles referenced on my blog) where they had survey'd light levels needed by various corals....they found, to put it in a nutshell, that levels from as low as 5,000 lux would meet most corals' so-called "compensation point" where photosynthesis production exceeds the costs+their metabolic needs.  5,000 lux ISN'T MUCH, and corals can be chemically very adept at these levels.  Corals have adaptations (which come at a cost/with risks) to thrive at shallower depths with more light than this – they do NOT "need" more light than this.  They are "at home" in low light.  (Recall that corals are only photosynthetic by way of their "infection" with dinoflagellates...it's not an inherent trait.  Corals are, at their phylogenetic root, a non-photosynthetic deep-water sessile scavenger/predator which is at home on the sea floor WITHOUT light.

 

Clams are the most notable exception among the critters we keep.  By comparison to corals, clams seem to have essentially no stress response to strong light, and have a fairly high minimum irradiant level of around 30,000 lux.  

 

Getting To Those Journals...

"The in situ light microenvironment of corals" is one article that gets into the nitty gritty of how corals use light, espeically in lower light situations.  Might be interesting.

"Novel Adaptive Photosynthetic Characteristics of Mesophotic Symbiotic Microalgae within the Reef-Building Coral, Stylophora pistillata" also focuses on corals in low light.

"Flicker Light Effects on Photosynthesis of Symbiotic Algae in the Reef- Building Coral Acropora digitifera (Cnidaria: Anthozoa: Scleractinia)." is another one I think is super interesting on the "maximum intensity" end of the lighting possibilities.

"Ocean Optics by Curtis Mobley" is another must-read for anyone deeply interested in coral lighting.

 

Last, you mentioned "growth" as one of the bellwethers....but we know that fast growth (eg from higher light levels) doesn't necessarily mean generally "healthier" corals as "Fast Growth May Impair Regeneration Capacity in the Branching Coral Acropora muricata" illustrates.

 

So in general your "gut" and experience are correct.  🙂 👍  I hope the links help!