Ideal PAR,,, but for how long?

[TbyZ]

Hi Dana if your viewing; I have a quick question.

I'm thinking about corals & all the things that affect zooxanthallae's ability to photosynthesize at their peak rate. In regards to par, if the ideal par value was know for any particular species of coral, what is typically the ideal duration of illumination at that par before the peak rate of photosynthesis falls?
I wouldn't imagine that a coral could remain at peak photosynthesis for 24 hours, for example.

thanks

 

[TbyZ]

 

[TbyZ]

Bump

 

[sbash]

Indeed...

I was just reading through: http://www.advancedaquarist.com/2009/5/aafeature and wondered the same thing. Based on what I got out of that article, several of my tanks are not running for long enough.

@Dana Riddle Can you please shed some *cough* light on the age-old debate (I am thinking based on the article I mention above) of how long we should really be running our lights?

 

[Dana Riddle]

The ideal lighting intensity/photoperiod would mimic the light history of the coral. But there are several problems:
1. We most likely don't know the light history of the coral.
2. We are concerned about coral growth.
3. We want to maintain or induce vivid coral coloration.
4. Maintenance costs are/should be a concern. Lighting and cooling (if needed) can be expensive!
5. Excessive nutrients can cause algal growths.
Hence, we maintain low nutrients levels. If we limit algal growths, we're probably limiting zooxanthellae as well. The coral becomes more dependent upon heterotrophy. If the nutritional requirements of the zoox is satisfied, then photosynthesis can proceed but we must sure we maximize the conditions for this to happen by compromising. The trick is to provide enough light to make sure enough photosynthesis is happening (that is, we meet the zoox compensation point - 100 micromole/m2/sec will almost certainly do the trick.) But we don't want to provide too much light - this can cause dynamic photoinhibition were the 'pressure relief valve' (the xanthophyll cycle) actually slows the rate of photosynthesis. Providing a maximum of perhaps 250-400 PAR should be sufficient and this will likely prevent chronic photoinhibition where the photosynthetic apparatus is damaged and much energy is expended in its repair. Fortunately, PAR of 250-400 will probably be enough to induce non-fluorescent coloration in many corals. Just remember that not all coral colors are light-loving (red fluorescent proteins are generally regarded to be found in deeper water or shaded corals. There are exceptions of course.) So, how long do I run the lights? If lighting is kept under the values that induce a lot of dynamic photoinhibition (or any chronic photoinhibition), the should be no problems in keeping the lights on for 10 to 14 hours a day. There is evidence that zooxanthellate reproduction cycles are interrupted when maintained in constant illumination, so obviously that isn't advisable.

 

[sbash]

There are exceptions of course.) So, how long do I run the lights? If lighting is kept under the values that induce a lot of dynamic photoinhibition (or any chronic photoinhibition), the should be no problems in keeping the lights on for 10 to 14 hours a day. There is evidence that zooxanthellate reproduction cycles are interrupted when maintained in constant illumination, so obviously that isn't advisable.

Awesome, thanks, Dana.

However, good answers lead to more questions

So, for those of us running multiple channels; are you suggesting we should be able to safely keep all channels (in my case white and blue) on for 10 to 14 hours?

Also, I have a couple systems only running (all channels) for about 6 hours. If I ramp those up over a month or so to 10 hours, I should (theoretically) start seeing better growth?

 

[Dana Riddle]

Awesome, thanks, Dana.

However, good answers lead to more questions

So, for those of us running multiple channels; are you suggesting we should be able to safely keep all channels (in my case white and blue) on for 10 to 14 hours?

Also, I have a couple systems only running (all channels) for about 6 hours. If I ramp those up over a month or so to 10 hours, I should (theoretically) start seeing better growth?

This answer will lead to more questions . Spectral issues come into play, if one of your channels is heavy in the red portion of the spectrum, it *possibly* could lead to zooxanthellae loss. This is very much an area that needs further investigation. The tanks I've seen running at very low PAR values are running all blue. Theoretically yes - you should see more growth if intensity and spectral qualities are in line.

 

[TheEngineer]

Can you quantify "heavy" as it relates to red light?

 

[Dana Riddle]

Can you quantify "heavy" as it relates to red light?

That's the issue that confronts us. Early researchers found light quality could affect zooxanthellate and their hosts:
Kinzie, R.A. and T. Hunter, 1987. Effect of light quality on photosynthesis of the reef coral Montipora verrucosa. Mar. Biol., 94:95-109.

Kinzie, R.A., 1993. Effects of ambient levels of solar ultraviolet radiation on zooxanthellae and photosynthesis of the reef coral Montipora verrucosa. Mar. Biol., 116:319-327.

Kinzie, R.A., P.L. Jokiel and R. York, 1984. Effects of light of altered spectral composition on coral zooxanthellae associations and on zooxanthellae in vitro. Mar. Biol., 78:239-248.
I saw it when using LEDs experimentally in 2002:
http://www.advancedaquarist.com/2003/11/aafeature
And, recently, others (Wijgerde et al.) examined the effects of red light. What we don't know is how much red light is required to impact corals/zoox symbioses. Now that I have a meter that can quantify chlorophyll content in a non-invasive manner, it is *only* a matter of developing the experiment's protocol, executing it, and analyzing data. *Sigh*

 

[TheEngineer]

Thanks for the references! I'll look for them. In the article @sbash linked to above, you show this image:

Do you think there's a timing associated with adding red lights where it would perhaps be less detrimental to the zoox? If red inhibits the G2/M phase, would only having red on during the last half of G1 and first half of S reduce the issues?

I'm slowly trying to get a better understanding for how the colors we see are affected by the zoox, I still don't get it...

 

[Dana Riddle]

Thanks for the references! I'll look for them. In the article @sbash linked to above, you show this image:

Do you think there's a timing associated with adding red lights where it would perhaps be less detrimental to the zoox? If red inhibits the G2/M phase, would only having red on during the last half of G1 and first half of S reduce the issues?

I'm slowly trying to get a better understanding for how the colors we see are affected by the zoox, I still don't get it...

Many questions, few answers. The 'colors we see' are the coral fluorescent/non-fluorescent proteins?

 

[TheEngineer]

Many questions, few answers. The 'colors we see' are the coral fluorescent/non-fluorescent proteins?

Yes, sorry. That wasn’t a clear statement when also referring to visual spectra of light.

Another questions in my mind is if red light causes this problem, why do corals in extremely shallow waters not have problems with their zoos? Do they capture it from deeper corals?

 

[Dana Riddle]

Yes, sorry. That wasn’t a clear statement when also referring to visual spectra of light.

Another questions in my mind is if red light causes this problem, why do corals in extremely shallow waters not have problems with their zoos? Do they capture it from deeper corals?

Based on my limited observations in Hawaiian shallow tide pools, I believe these corals do suffer greatly. Growth is stunted likely due to energy reserves being channeled to repair. Zoox concentrations on exposed sides were, at some points, zero while shaded sides had chlorophyll concentrations of over 200 mg/m2.

 

[TbyZ]

Yes, sorry. That wasn’t a clear statement when also referring to visual spectra of light.

Another questions in my mind is if red light causes this problem, why do corals in extremely shallow waters not have problems with their zoos? Do they capture it from deeper corals?

24 Feb 2017
Coral mortality induced by the 2015–2016 El-Niño in Indonesia: the effect of rapid sea level fall
Eghbert Elvan Ampou1,2,3, Ofri Johan4, Christophe E. Menkes5, Fernando Niño3, Florence Birol3, Sylvain Ouillon3, and Serge Andréfouët1,2

Abstract. The 2015–2016 El-Niño and related ocean warming has generated significant coral bleaching and mortality worldwide. In Indonesia, the first signs of bleaching were reported in April 2016. However, this El Niño has impacted Indonesian coral reefs since 2015 through a different process than temperature-induced bleaching. In September 2015, altimetry data show that sea level was at its lowest in the past 12 years, affecting corals living in the bathymetric range exposed to unusual emersion. In March 2016, Bunaken Island (North Sulawesi) displayed up to 85 % mortality on reef flats dominated by Porites, Heliopora and Goniastrea corals with differential mortality rates by coral genus. Almost all reef flats showed evidence of mortality, representing 30 % of Bunaken reefs. For reef flat communities which were living at a depth close to the pre-El Niño mean low sea level, the fall induced substantial mortality likely by higher daily aerial exposure, at least during low tide periods. Altimetry data were used to map sea level fall throughout Indonesia, suggesting that similar mortality could be widespread for shallow reef flat communities, which accounts for a vast percent of the total extent of coral reefs in Indonesia. The altimetry historical records also suggest that such an event was not unique in the past two decades, therefore rapid sea level fall could be more important in the dynamics and resilience of Indonesian reef flat communities than previously thought. The clear link between mortality and sea level fall also calls for a refinement of the hierarchy of El Niño impacts and their consequences on coral reefs.

https://www.biogeosciences.net/14/817/2017/