Acclimatization of Symbiotic Corals through Wavelength Transformation by Fluorescent Protein Pigments

[Nano sapiens]

Having read through a multitude of threads espousing the benefits, or not, of 'complete spectrum' (relatively speaking), I found this article the other day and had the chance to really dig into the nitty-gritty bits today:

Acclimatization of symbiotic corals to mesophotic light environments through wavelength transformation by fluorescent protein pigments

While a bit involved, I do think it's the worth the effort and time required to grasp the implications of how corals have adapted to the predominately blue light field found at mesophotic (~45 meters) depths. What was discovered has implications for the current all blue wavelength lit reef aquaria, especially in medium/low PAR environments.

The big takeaway for me was that brownish corals (Lobophyllia hemprichi and Echinopora sp.) at lower light levels of around 25 PAR found at ~45 meters depth (basically all 'bluish' light) had 100% mortality after 2 years in those conditions. Those same two species (same conditions) that had pcRFP pigmentation (photo convertible, from green to red, Red Fluorescent Pigmentation) had 0% mortality. The pcRFP pigmentation exists in the upper epidermis layer and converts blue light to orange/red which then has the ability to penetrate the coral tissue to a greater depth (nourishing the deeper living zooxanthellae) as well as scattering the light more broadly to benefit many more of the aforementioned zooxanthellae.

An interesting excerpt (refers to the Gulf of Eilat):

While completely absent in the shallowest surveyed depth of 1 m, the proportion of red fluorescent coral colonies increases with depth, reaching 30% at 45 m depth.

I doubt many of us are running 25 PAR reefs , but the findings are still relevant to reef keepers running all blue lower light level reefs and can help to explain why certain corals in the population simply fade away over extended periods of time.

 

[KrisReef]

Thanks for posting this.

 

[taricha]

This is interesting to me in a slightly different direction.
Hobby is full of advice saying that when trying to starve algae (like dinos) of light, but give a minimum to corals, you should use actinic or far blue only.

But if you dive deep into the dinoflagellate photosynthetic pigments, this makes little sense. The problem dinos and our coral symbiont dinos have exactly the same pigments. so playing games with moving the light spectrum around seems senseless.

BUT...
far blue / actinic light misses Chl C , and peridinin entirely and almost misses Chl A. So inside a fluorescent coral, the blue incoming light gets shifted to more useful wavelengths, so it's plausible that far blue selectively gives light to symbitic dinos inside fluorescent coral while light-starving dinos and other algae outside the coral. Plausible anyway.

So maybe the anecdotal hobby advice was right all along...

 

[KrisReef]

This is interesting to me in a slightly different direction.
Hobby is full of advice saying that when trying to starve algae (like dinos) of light, but give a minimum to corals, you should use actinic or far blue only.

But if you dive deep into the dinoflagellate photosynthetic pigments, this makes little sense. The problem dinos and our coral symbiont dinos have exactly the same pigments. so playing games with moving the light spectrum around seems senseless.

BUT...
far blue / actinic light misses Chl C , and peridinin entirely and almost misses Chl A. So inside a fluorescent coral, the blue incoming light gets shifted to more useful wavelengths, so it's plausible that far blue selectively gives light to symbitic dinos inside fluorescent coral while light-starving dinos and other algae outside the coral. Plausible anyway.

So maybe the anecdotal hobby advice was right all along...

I’m lost at “light shifting wavelengths” (in these discussions). My understanding of light physics and energy can’t allow this to happen-@least in my formal understanding of how things work?
But your understanding seems correct at least in the light of busy hobbiest figuring out what to do to make things work in our tanks before the science catches up.

 

[oreo54]

I’m lost at “light shifting wavelengths” (in these discussions). My understanding of light physics and energy can’t allow this to happen-@least in my formal understanding of how things work?
But your understanding seems correct at least in the light of busy hobbiest figuring out what to do to make things work in our tanks before the science catches up.

Refers to the conversion via flourescence.

Taking in blue light and converting to internally to say green or red photons ala Stokes shift. Then using those photons for photosynthesis.

Stokes shift - Wikipedia

en.wikipedia.org

Only would benefit corals that have flourescent pigments or a very close to one.

 

[KrisReef]

Refers to the conversion via flourescence.

Taking in blue light and converting to internally to say green or red photons ala Stokes shift. Then using those photons for photosynthesis.

Stokes shift - Wikipedia

en.wikipedia.org

Thank you! I will have to put my nose in some books and catch up on these things!

 

[oreo54]

Thank you! I will have to put my nose in some books and catch up on these things!

Get the glow: the secret to deep-water corals’ radiance - Nature

Organisms use red fluorescent protein to optimize light for photosynthesis.

www.nature.com

However, says Wiedenmann, the study shows that the protein pigments expressed by shallow corals are “biochemically and optically distinct” from those of their deep-dwelling counterparts. “Not many of them may have the capacity to escape to deeper waters,” he says.

 

[Nano sapiens]

This is interesting to me in a slightly different direction.
Hobby is full of advice saying that when trying to starve algae (like dinos) of light, but give a minimum to corals, you should use actinic or far blue only.

But if you dive deep into the dinoflagellate photosynthetic pigments, this makes little sense. The problem dinos and our coral symbiont dinos have exactly the same pigments. so playing games with moving the light spectrum around seems senseless.

Ah, so what do we know about coral associated dinoflagellate photosynthetic pigments?

https://eatlas.org.au/content/gbr-gci-symbiodinium-clade-distribution-article

'So far, all clades except E, H and I have been found in corals although on the Great Barrier Reef most corals harbour Symbiodinium types from clade C and to a lesser extent clade D. Clade E is found in anemones and clade F, G, H and I are common among foraminifera. Each of these clades contains genetically and ecologically distinct subcladal types or strains. These types can, but do not necessarily have to be, different Symbiodinium species. Subcladal types often only differ by a few nucleotides. Yet, they may vary distinctively in their physiological characteristics; from differences in symbiont size and pigment composition to differences in heat stress tolerance.'

I don't know much about the various free living dinoflagellate pigments, but it may be that they are species specific or the organism may be able to alter them based on conditions?

Down the rabbit hole we go

BUT...
far blue / actinic light misses Chl C , and peridinin entirely and almost misses Chl A. So inside a fluorescent coral, the blue incoming light gets shifted to more useful wavelengths, so it's plausible that far blue selectively gives light to symbitic dinos inside fluorescent coral while light-starving dinos and other algae outside the coral. Plausible anyway.

So maybe the anecdotal hobby advice was right all along...

Interesting idea and sounds plausible for those corals with wavelength altering pigmentation such as pcRFP. But then there are many corals that don't have this same ability.

I'm going to ramble a bit here, but I find it interesting to ponder the theoretical consequences of running only 'far blue/actinic' light at the higher intensities typically seen in reef aquaria (something not found in nature).

Looking at a mesophotic coral with pcRFP, it alters the weak intensity (~25 PAR) broad spectrum blue light towards orange/red and these wavelengths, while not being as optimal for zooxanthellae photosynthesis as blue, do however penetrate much deeper into the coral's tissues and also back-scatter against the skeleton which nourishes a substantial population of the more deeply embedded symbionts. Corals without this type of pigment at these depths either have to get by on the reduced intensity broad spectrum blue light, possibly have other tricks up their sleeves that I am not aware of/have yet to be discovered, and/or utilize different symbiodinium clades that have pigments that can more efficiently utilize the reduced available light.

In a reef aquarium example with just far blue/actinic, a large portion of the upper blue spectrum is weakly represented (or possibly missing altogether). In this case, what reefers are doing (whether they know it or not) is compensating by using a higher intensity in an attempt to drive sufficient zooxanthellae photosynthesis. Some corals will adapt to this, others not so much, and those with pcRFP may find that the conversion to orange/red at the higher intensities causes bleaching (detrimental overabundance of red light, as has been demonstrated by Dana Riddle and others)...and so decrease or loose their pcRFP completely under these circumstances.

 

[oreo54]

Want to complicate deep water photosynthesis even more?

Calculations have shown that at the great depths the peredinin absorbance corresponds to 42% of total cell absorbance and that the increase of light absorbance correlating with changes of its spectral characteristics is entirely determined by presence of this carotenoid. The increase of amount of peridinin in cell is as much important as important the increase of all other pigments taken together. However, at the same time selective and preferential accumulation of peridinin and the change of its native state in the limits naturally occurred in zooxanthellae cells have only low impact on the light absorbance. The presence of peridinin could be considered as manifestation of chromatic adaptation of organism. The comparison of light absorption by zooxanthellae with different content of peridinin (or without peridinin) reveals that this pigment expands the habitat of hermatypic corals in ocean waters at 8-17 meters into the deep.

https://www.researchgate.net/publication/7767152_Light_absorption_by_carotenoid_peridinin_in_zooxanthellae_cell_and_setting_down_of_hermatypic_coral_to_depth

Or generally...

Frontiers | Photosynthetic Acclimation of Symbiodinium in hospite Depends on Vertical Position in the Tissue of the Scleractinian Coral Montastrea curta

Coral photophysiology has been studied intensively from the colony scale down to the scale of single fluorescent pigment granules as light is one of the key ...

www.frontiersin.org

The external light field is a poor proxy for the internal
light microenvironment experienced by the coral symbionts
(Kaniewska et al., 2011).

Addendum..

Our study of Symbiodinium photosynthesis in hospite under
real tissue light gradients was done under red illumination.
The role of spectral composition is undeniably important as it
affects processes such as light harvesting (Vogelmann and Han,
2000; Szabó et al., 2014), photoinhibition (Oguchi et al., 2011),
respiration (Wangpraseurt et al., 2014c), CO2 fixation (Sun et al.,
1998), and O2 production (Kühl et al., 1995), and we note that

Lichtenberg et al. Photosynthetic Acclimation of Symbiodinium in hospite
the results may differ under white light illumination, although the
internal light field in coral tissues is red shifted

 

[Nano sapiens]

Want to complicate deep water photosynthesis even more?

https://www.researchgate.net/publication/7767152_Light_absorption_by_carotenoid_peridinin_in_zooxanthellae_cell_and_setting_down_of_hermatypic_coral_to_depth

Or generally...

Frontiers | Photosynthetic Acclimation of Symbiodinium in hospite Depends on Vertical Position in the Tissue of the Scleractinian Coral Montastrea curta

Coral photophysiology has been studied intensively from the colony scale down to the scale of single fluorescent pigment granules as light is one of the key ...

www.frontiersin.org

Yup, 'Down the rabbit hole we go'

 

[taricha]

I’m lost at “light shifting wavelengths” (in these discussions).

Yep, here's two examples from my system. I extracted water soluble fluorescent pigments from a few of my corals. (Sorry guys, no acros. You'll have to read papers from the pros for that.)

This one is from a green toadstool leather. Exciting the extracted pigment with a 448nm LED, it emits the curve in green - photons from 490-540nm are well represented.

And here's one from a candy cane.
exciting it with 405nm, it gives off a good amount of light from 450-530nm.

Only would benefit corals that have flourescent pigments or a very close to one.

Interesting idea and sounds plausible for those corals with wavelength altering pigmentation such as pcRFP. But then there are many corals that don't have this same ability.

true, and the hobby has been selecting for corals with those traits - bright fluorescence in response to blue light. So most hobby corals will fit here.

compare the above emission of green light from the fluorescent pigments to the absorption curve of the peridinin-chlorophyll protein complex - the workhorse of dinoflagellate light harvesting.

In high light, fluorescence probably doesn't matter much for light gathering of the symbiont, but in low "actinic-only" light, it may well be important.

 

[KrisReef]

I think this quote sums up a bit of this light subject:
“The external light field is a poor proxy for the internal
light microenvironment experienced by the coral symbionts
(Kaniewska et al., 2011).”

(I’m supposed to be working, you guys are awesome !)I think I will sell my PAR meter now that it has been shown to be functionally useless.? Who measures internal light fields and how much does that meter cost?

 

[Nano sapiens]

I think I will sell my PAR meter now that it has been shown to be functionally useless.? Who measures internal light fields and how much does that meter cost?

Considering the intricacies of measuring internal light fields (and who knows how many thousands of dollars for the specialty instruments), a PAR meter is an appropriate/relatively affordable tool for reef hobbyists.

 

[Nano sapiens]

Yep, here's two examples from my system. I extracted water soluble fluorescent pigments from a few of my corals. (Sorry guys, no acros. You'll have to read papers from the pros for that.)

This one is from a green toadstool leather. Exciting the extracted pigment with a 448nm LED, it emits the curve in green - photons from 490-540nm are well represented.

And here's one from a candy cane.
exciting it with 405nm, it gives off a good amount of light from 450-530nm.

Nice, the excitation and emissions spectra line up neatly with what has been previously noted:

In high light, fluorescence probably doesn't matter much for light gathering of the symbiont, but in low "actinic-only" light, it may well be important.

That makes sense.

I find it fascinating that we see coral fluorescence which helps mitigate the potential harmful effects of high illumination in regards to the zoox, but then we also see coral fluorescence used to directly benefit them when in lower light environments.

Corals using the same device (fluorescence), but resulting in different ways of caring for it's symbiotic partners.

 

[oreo54]

Lot of florescence at 450-525nm....
Coincidence?

PerCP (Peridinin-Chlorophyll-Protein Complex)​