Interesting reports according Darwin's Paradox

[Lasse]

Since my beginning as reefer and holding corals I always has said that it would be very strange from a biological energy conservation point of view if not the coral animal eat and digest at least a part of the algal residents in their tissue. Many has understand that the coral animal must in one or another way control the amount of algae in their tissue but most people seems to believe that the coral animal just repel excess algae from their tissue. For me - it has not been an answer in line with how energy conservation works in nature. For me - it has been more likely that coral animal just farm the resident algae and consumed the surplus algae in order to use their nutrients in favor for the animal host. It has been no evidence for this in science literature - I have based my thoughts mostly from other known patterns of energy conservation in nature and from a philosophic point of view.

However - yesterday an article was published in Nature that strongly support the farmer theory

Reef-building corals farm and feed on their photosynthetic symbionts - Nature

Long-term experiments show that corals acquire dissolved inorganic nitrogen and phosphorus by feeding on symbiont cells, which provide essential nutrients enabling their success in nutrient-poor waters.

www.nature.com

Sincerely Lasse

 

[Lasse]

From Science.org

https://www.science.org/content/article/hard-working-farmers-corals-cultivate-and-eat-their-resident-algae

Sincerely Lasse

 

[taricha]

was just reading this paper. Interesting that they showed a bunch of corals (including common hobby ones) could grow successfully with just NO3 and PO4, and they stripped / sterilized all particulates from the water.
Makes you wonder if we overthink "optimal" nutrient forms for corals when the symbionts can take in plain old NO3 + PO4 and the corals can just eat the symbionts.

 

[Lasse]

was just reading this paper. Interesting that they showed a bunch of corals (including common hobby ones) could grow successfully with just NO3 and PO4, and they stripped / sterilized all particulates from the water.
Makes you wonder if we overthink "optimal" nutrient forms for corals when the symbionts can take in plain old NO3 + PO4 and the corals can just eat the symbionts.

For me - the recipie is simple: Sea water with natural parameters, light, corals and nutrients

Sincerely Lasse

 

[Lasse]

More explanations of the article

Vegetarian diet of corals explains age-old mystery dating back to Darwin - Lancaster University

A new study has revealed why coral reefs can thrive in seemingly nutrient poor water, a phenomenon that has fascinated scientists since Charles Darwin.

www.lancaster.ac.uk

Sincerely Lasse

 

[Subsea]

https://www.science.org/content/article/hard-working-farmers-corals-cultivate-and-eat-their-resident-algae

Could the algae somehow be passing these nutrients along to their coral hosts?

@Lasse
I have found research to this point. And will find it and link it here. in a bit.

My paraphrase

“microbes in surface film cross-talked with microbes in interior of biomass and altered environmental conditions to their advantage”

Sounds like co-op farming. Let’s farm this topic together.
A Cajun Aggie in Texas,
Patrick

PS. This is not the article I want, yet it supports your theory on this.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4711185/

 

[Lasse]

Could the algae somehow be passing these nutrients along to their coral hosts?

Yes - as food

Sincerely Lasse

 

[Subsea]

Microbes in the coral holobiont: partners through evolution, development, and ecological interactions

In the last two decades, genetic and genomic studies have revealed the astonishing diversity and ubiquity of microorganisms. Emergence and expansion of the human microbiome project has reshaped our thinking about how microbes control host health—not only as pathogens, but also as symbionts. In...

www.frontiersin.org

In the last two decades, genetic and genomic studies have revealed the astonishing diversity and ubiquity of microorganisms. Emergence and expansion of the human microbiome project has reshaped our thinking about how microbes control host health—not only as pathogens, but also as symbionts. In coral reef environments, scientists have begun to examine the role that microorganisms play in coral life history. Herein, we review the current literature on coral-microbe interactions within the context of their role in evolution, development, and ecology. We ask the following questions, first posed by McFall-Ngai et al. (2013) in their review of animal evolution, with specific attention to how coral-microbial interactions may be affected under future environmental conditions: (1) How do corals and their microbiome affect each other's genomes? (2) How does coral development depend on microbial partners? (3) How is homeostasis maintained between corals and their microbial symbionts? (4) How can ecological approaches deepen our understanding of the multiple levels of coral-microbial interactions? Elucidating the role that microorganisms play in the structure and function of the holobiont is essential for understanding how corals maintain homeostasis and acclimate to changing environmental conditions.

 

[Subsea]

My bad, I finally read your last link.

“The coral animals are dependent on a ‘symbiosis’, a mutually beneficial relationship with microscopic algae that live inside their cells. The photosynthetic algae produce large amounts of carbon-rich compounds, such as sugars, which they transfer to the host coral for energy generation.”

“The symbiont algae are also very efficient in taking up dissolved, inorganic nutrients from sea water, such as nitrate and phosphate. Even in nutrient poor oceans, these compounds can be found in considerable amounts as excretion products of organisms, such as sponges, that live close by.”

Lasse,
Eureka I have Found It. (Attributed to Archimedes)

This article identifies specific Cynobacteria that perform that purpose.

Discovery of symbiotic nitrogen-fixing cyanobacteria in corals - PubMed

Colonies of the Caribbean coral Montastraea cavernosa exhibit a solar-stimulated orange-red fluorescence that is spectrally similar to a variety of fluorescent proteins expressed by corals. The source of this fluorescence is phycoerythrin in unicellular, nonheterocystis, symbiotic cyanobacteria...

pubmed.ncbi.nlm.nih.gov

Abstract​

Colonies of the Caribbean coral Montastraea cavernosa exhibit a solar-stimulated orange-red fluorescence that is spectrally similar to a variety of fluorescent proteins expressed by corals. The source of this fluorescence is phycoerythrin in unicellular, nonheterocystis, symbiotic cyanobacteria within the host cells of the coral. The cyanobacteria coexist with the symbiotic dinoflagellates (zooxanthellae) of the coral and express the nitrogen-fixing enzyme nitrogenase. The presence of this prokaryotic symbiont in a nitrogen-limited zooxanthellate coral suggests that nitrogen fixation may be an important source of this limiting element for the symbiotic association.
PubMed Disclaimer

 

[Lasse]

In this thread a huge discussion about nitrogen in the water column as a limited factor for algae but not photosynthesizing corals started. I decide to move my answers and thoughts to this thread that I have started by myself because my arguments is mainly build on the report mentioned in this thread.

First a quote from the article showing the predominant thoughts about the symbiosis partnership till now. From here. My bold

Symbiotic corals function as mixotrophs in which the metabolic carbon demand of the animal host can often be met by the translocation of carbon-rich photosynthetic products from their dinoflagellate symbionts 2,3. Although this carbon transfer sustains the host’s energy production, it cannot promote its growth 10. Instead, the host is thought to take up nitrogen (N) and phosphorus (P) in a favourable stoichiometry required to produce the essential building blocks for growth and reproduction mostly by feeding on particulate or dissolved organic material, including plankton and dissolved free amino acids 11,12,13. The symbionts benefit from host heterotrophy by recycling N- and P-rich excretion products of the host metabolism that they can then use to promote their own growth 11,12,14. Retaining these valuable compounds within the symbiotic association is considered the other main function of the photosynthetic partner 10.

From the same sub chapter in the report

Previous studies using isolated symbionts suggested that only small quantities of N in the form of amino acids are released from the symbiont cells and might be available to the host5,7,8,9. More recently, nanoscale secondary ion mass spectrometry (NanoSIMS) experiments have visualized the translocation of 15N from the symbiont, the prominent site of N uptake, to the host16,18. Also, the translocation of substantial amounts of N from the symbiont to the host has been observed in an Acropora coral in the wild6. Furthermore, recent studies indicate that considerable amounts of N-rich amino acids in the host tissue originate from the symbionts16,19,20,21. At present, there is no evidence for the symbiont-to-host transfer of phosphorus11. In fact, symbionts are considered a phosphorus sink within the symbiosis4. Therefore, current knowledge cannot explain host growth-promoting effects of dissolved inorganic N and P described by several studies of corals in experimental settings and in the natural environment22,23,24,25,26,27,28,29. Consequently, a key mechanism controlling the productivity of the world’s coral reefs remains insufficiently understood; a fact that is of particular concern because dissolved inorganic nutrients can represent locally or temporarily the most significant sources of N or P in otherwise nutrient-poor tropical waters (Extended Data Fig. 1).

From next chapter - still my bold

Supply of dissolved inorganic N and P has two potential consequences for symbiotic corals. First, nutrients become directly available to the symbionts15,22,28,32,41,42. Second, nutrients can increase the productivity of the wider natural or experimental ecosystem20,31, yielding increased particulate organic N and P that may serve as food to the coral animal host20. Therefore, quantifying the extent to which each partner in the coral–dinoflagellate symbiosis benefits from increased nutrient levels is notoriously difficult. Here, we reveal a mechanism by which coral animals profit from dissolved inorganic N and P, bridging the gap in the understanding how this important pool of nutrients can promote coral growth and reef development. We report the results of a series of long-term time course experiments in tightly controlled nutrient conditions in the laboratory43,44,45 to test the direct effects of dissolved inorganic N and P on the growth of ten common coral species.

The experiment was set up in order to see whats happen if the corals only had access to dissolved inorganic N and P in the water column. The time scale was more than 6.5 months. NO3 and PO4 was chosen as inorganic N an P sources because - still my bold from here

Coral animals have the capacity to incorporate some ammonium (NH4+) directly15,16. However, this direct uptake pathway is quantitively trivial compared to the 14–23 times higher NH4+ assimilation rates of their symbionts16. By contrast, coral hosts cannot directly assimilate nitrate (NO3) because the animal tissue lacks the required enzymes15,17. Therefore, NO3 uptake and assimilation proceeds exclusively through the symbionts18. The same applies to phosphorus in its dissolved inorganic form (PO4)11.

The set up

We exposed 10 replicate colonies for each of the 9 hard and one soft coral species to either replete or limiting concentrations of nitrate and phosphate for more than 6.5 months (Supplementary Fig. 1 and Methods). Nutrients in these chemical forms cannot be directly assimilated by the animal hosts and particulate material that could potentially serve as food was removed by UV sterilization and microfiltration before the water entered the flow-through tanks with the experimental corals. For corals kept in the nutrient-limited aquarium system, growth and calcification started to stagnate after around 50 days (Fig. 1a–c). Over the same period, these corals lost more than half of their symbiont population, resulting in a bleached appearance (Fig. 1a,b). By contrast, in the nutrient-replete system, the corals grew and calcified at an exponential rate (Fig. 1b–d), whereas symbiont density remained constant (Fig. 1b,d). By the end of the experiment, the coral area covered with live tissue had increased by approximately threefold in corals living in nutrient-replete conditions, indicating a concomitant increase of host and symbiont biomass

The increase in host biomass per colony grown under nutrient-replete conditions corresponds to an average gain of 0.25 mg P and 2.44 mg N. Because the coral hosts were deprived of particulate food in our experiments, this gain in N and P indicates an efficient uptake of dissolved inorganic N and P by the symbiont and subsequent transfer to the host.

If we translate the gain in mg to gain in mmol (of N and P) and get an atomic ratio of N/P we get 1/14*2,14 mmol N and 1/31*0.25 mmol P -> 0.15 mmol N and 0.008 mmol P which will give a mol ratio of 0.15N/0.008P = around 19/1 (mol ration= atomic ratio) as N/P. In the experiment they use (method)

Corals were kept in nutrient-replete conditions ([NO3] ≈ 12 µM, [PO4] ≈ 3 µM), simulating nutrient environments that have been previously described for reefs with increased coral growth rates

This is an atomic ratio of 4/1. 12 µM = 12 µmol/L = 12*62 µg/L = 0,74mg/L NO3 and 3 µM =3 µmol/L = 3*95 µg/L = 0,285 mg/L PO4. With a PO4 of 3 µM - to have the same ratio as the gain above you should have 54 µM NO3. 3 µM P= 3µM PO4 and 12 µM N = 12 µM NO3. 54 µM NO3 = 54*62 µg/L = 3,348 mg/L NO3.
In mg/L the NO3/PO4 ratio is around 12/1

They also did a N labeled experiment with nutrient pulses 5 day a week. In that experiment they calculate How much of N and P that was taken from the water and afterwards was found in the zooxanthellae respective animal tissue. Among the interesting things was this

gain of around 4.8 µmol N and 0.14 µmol P by the symbiont tissue and around 8.4 µmol N and 0.35 µmol P by the host tissue

This correspond to an atomic quota of around 34/1 N/P in the zoox and 24/1 in the tissue.

They have also linked this to natural reefs and found the same - nutrients you find in the water column is found in the hosts tissue and the pathway is that they are captured by the zooxanthellae and transfered as food to the animal.

As I see it - there have been very few persons in the hobby that have realized this turning point how we should look at the the relationship between zooxanthellae and the coral animal. As far as I understand, this cannot be described as a symbiosis any longer - more as slavery and I feed on your offsprings relationship.

Sincerely Lasse

 

[BeanAnimal]

was just reading this paper. Interesting that they showed a bunch of corals (including common hobby ones) could grow successfully with just NO3 and PO4, and they stripped / sterilized all particulates from the water.
Makes you wonder if we overthink "optimal" nutrient forms for corals when the symbionts can take in plain old NO3 + PO4 and the corals can just eat the symbionts.

I just saw this thread. Interesting. I would ask though, is this a survival mechanism more than a long term functional mechanism?

Not a parallel, but your body will start to consume itself if outside nourishment is not provided at sufficient levels.

 

[jda]

I had a similar thought to BeanAnimal... are we sure that the slavery and feeding as described is not just because the researchers created a poor environment? ...stress response, or sorts.

I appreciate the thought and articles. I would love to see a second article, or more. I will be keeping an eye out and remembering this if one every comes.

 

[danimal1211]

Just an observation for it has been understood for some time that dosing aminos has no apparent benefit in higher nutrient systems. I would suspect dosing NH4 to be similar. my nitrates usually stay ~10ppm but when I tried dosing NH4 they shot up to 15. I have suspended the dosing and am bringing them back down.
Could corals and their symbionts actually be showing preference for NO3 vs other nitrogen sources

 

[jda]

Just an observation for it has been understood for some time that dosing aminos has no apparent benefit in higher nutrient systems. I would suspect dosing NH4 to be similar. my nitrates usually stay ~10ppm but when I tried dosing NH4 they shot up to 15. I have suspended the dosing and am bringing them back down.
Could corals and their symbionts actually be showing preference for NO3 vs other nitrogen sources

I have thought about this quite a bit and the only thing that I could reason is that the corals would have to have a surplus of energy to need to use up. However, if they had all of this extra energy and no shortage of building blocks, they could just grow.

I have never seen anybody suggest or recommend that corals get their N from no3... just that they can if they have to. However, anybody can be wrong so the thought and discussion is good.

Others might disagree.

As for aminos, it does not appear that all of them act the same and can be used in the same way. Do you happen to know which actual amino (or aminos) you are speaking of? Some metabolize almost instantly, some might stay together longer, some won't keep together in the bottle, etc. I guess that my point is since nearly nobody knows the actual amino acids that are in most products (one used to list the actual aminos on the bottle), then I might suggest that analyzing aminos not be done too hard?

 

[danimal1211]

I can’t say specifically which ones. I do know ME corals specifically says their product is for low nutrient systems, that high N03 systems will not benefit.

 

[KrisReef]

For me - the recipie is simple: Sea water with natural parameters, light, corals and nutrients

Sincerely Lasse

I have parakeets at home and I am thinking of setting up their perch directly over my refugium. Am I over thinking this one?

Un-sincerely,
Kris

 

[taricha]

I would ask though, is this a survival mechanism more than a long term functional mechanism?

I had a similar thought to BeanAnimal... are we sure that the slavery and feeding as described is not just because the researchers created a poor environment?

It's certainly a mechanism that is used in starvation, but not only that.
Check out the figure 1b in the article. It shows what the corals looked like from the beginning throughout the experiment.
The corals that were starved still grew somehow for months. They are the saddest palest things ever, but they still grew to some extent - in part by eating their symbionts - and they end up dead/near dead and white. So certainly a mechanism used in starvation.
The other corals that had NO3+PO4 ate their symbionts but the symbionts grew on NO3 + PO4 and they look, well, normal. They seem very much like how we'd see those corals in the hobby.
Would the corals be happier with some aminos, phyto, etc? maybe - that wasn't tested in this experiment. But you'd have to answer a different question there. In cases where the coral host is well-fed directly from water and doesn't need to eat its symbionts, how does the coral control the symbiont growth? It can either clamp down chemically somehow on what nutrients it lets through to the symbionts, or it expels the extra symbionts it doesn't need, or eats them anyway and sheds the excess nutrients as sugars, mucus, dissolved organics etc.

this part of Lasse's post also is a good answer on this Q

They have also linked this to natural reefs and found the same - nutrients you find in the water column is found in the hosts tissue and the pathway is that they are captured by the zooxanthellae and transfered as food to the animal.

"Coral animals have the capacity to incorporate some ammonium (NH4+) directly15,16. However, this direct uptake pathway is quantitively trivial compared to the 14–23 times higher NH4+ assimilation rates of their symbionts16. By contrast, coral hosts cannot directly assimilate nitrate (NO3) because the animal tissue lacks the required enzymes15,17. Therefore, NO3 uptake and assimilation proceeds exclusively through the symbionts18. The same applies to phosphorus in its dissolved inorganic form (PO4)11."

We could ask the Q why corals can get away with being so bad at taking up commonly available N & P forms in the water, while their symbionts are so good at it. It seems a crippling limitation unless munching on the symbiont is - in fact - a typical nutrition pathway.

 

[BeanAnimal]

Thank you for the reply. I need to take it and the citations and digest. I fear I did not peruse, but rather browsed.

 

[jda]

Something still seems off to me. I am mostly into acropora, so my apoligies since I focus on that.

Fast growing acropora do not have enough symbionts to populate the new growth and tissue. It takes a while for the zoox to be able to populate these areas, which is why the color is different and/or white in the leading edges. I am talking thriving corals with significant growth - ideal, if you will.

I wish that they would have included some other sources of nitrogen and phosphorous in their study. I would feel better about their conclusions if they same thing happened with ample fish waste in a system. Otherwise, this will all just feel like a study of what happens when corals get stressed.

It also makes sense to me that the host does not have to accumulate much of their own building blocks since they can recycle what they have and also steal from their symbionts.

This might not apply here, but there are examples of hosts being complete savages with Tridacna clams growing and digesting their zoox for energy under any conditions.

 

[Lasse]

My bold

We exposed 10 replicate colonies for each of the 9 hard and one soft coral species to either replete or limiting concentrations of nitrate and phosphate for more than 6.5 months

Still my bold

For corals kept in the nutrient-limited aquarium system, growth and calcification started to stagnate after around 50 days (Fig. 1a–c). Over the same period, these corals lost more than half of their symbiont population, resulting in a bleached appearance (Fig. 1a,b). By contrast, in the nutrient-replete system, the corals grew and calcified at an exponential rate (Fig. 1b–d), whereas symbiont density remained constant (Fig. 1b,d). By the end of the experiment, the coral area covered with live tissue had increased by approximately threefold in corals living in nutrient-replete conditions, indicating a concomitant increase of host and symbiont biomass. We used a subset of these experimental corals (Montipora foliosa, Montipora capricornis, Acropora polystoma and Stylophora pistillata) to determine the N and P content of the tissue covering the expanded coral area. The increase in host biomass per colony grown under nutrient-replete conditions corresponds to an average gain of 0.25 mg P and 2.44 mg N. Because the coral hosts were deprived of particulate food in our experiments, this gain in N and P indicates an efficient uptake of dissolved inorganic N and P by the symbiont and subsequent transfer to the host.

IMO - 3 times larger area covered by coral tissue as an average after 6 months is not a survival mechanism. you can compare with area growth of non-photosynthesizing corals

I have never seen anybody suggest or recommend that corals get their N from no3... just that they can if they have to. However, anybody can be wrong so the thought and discussion is good.

I´m afraid that you need sooner or later rethink this. Think from an evolutionary standpoint. NO3 is by far the predominant inorganic N species in seawater even over reefs that get N inputs from guano - my bold as usally, According to the background of the natural distribution of NO3 and NH4 in the sea - IMO - uptake of NO3 is normal and that they beneficially absorb NH4/NH3 on the occasions when it is freely available

The deposition of seabird guano, specifically, can introduce significant amounts of nitrogen and phosphorus to reef systems28,38,39,40. Indeed, the amount of N available in dissolved inorganic form, mostly nitrate, in reefs close to seabird colonies can be about 90-fold higher than the amount available to corals in the form of zooplankton in reefs elsewhere

From here

however nitrate concentrations were significantly elevated for both sampling intervals at the seabird site. Large bird populations on small islands can result in extremely high nitrate concentrations in groundwater, which is advected into adjacent coastal lagoons33. In this study, despite nitrate concentrations above thresholds considered harmful to corals64,65, the A. formosa fragments growing near the seabird nesting island remained healthy during the experiment, grew vigorously and had endosymbiont cell densities considered optimal67 for branching corals68,69,70 to maintain photosynthetic performance71. The findings provide an interesting perspective on the contested issue of whether excess nutrients are harmful or beneficial to coral reefs

From the same article but especially for @Hans-Werner Its about the A formosa that grew vigorously in the quote above

Seabird guano elevates dissolved organic nitrogen32, inorganic nitrogen15,16 and phosphate concentrations in seawater15,58. In this study, there was no significant difference in measured phosphate concentrations between Namena and Cousteau, despite differences in seabird populations. Phosphate fluxes may have been higher from seabird guano, however if this is assimilated readily by benthic organisms it would not show in the water column concentrations. Nevertheless, phosphate concentrations were elevated and not limiting at both sites64,65, suggesting that the endosymbionts were replete in phosphorus to support coral growth and metabolism66. Nitrogen concentrations in the water column, in comparison, were significantly different between sites with ammonia and nitrate significantly elevated at the seabird site (Namena) compared to Cousteau and other coastal sites in Fij

It takes a while for the zoox to be able to populate these areas, which is why the color is different and/or white in the leading edges. I am talking thriving corals with significant growth - ideal, if you will.

There is different types of calcification - among many species it is in the top of the branches or in the edge of the colonies. First the skelet - after that place for the animal to grow. Acropora is for me one of the species that have most of the calcification on the outside of the colony


Sincerely Lasse