Coral Biology/Chemistry questions

[Tennyson]

Does anybody know how a coral works from a biology/chemistry standpoint?
I'd like to know more about coral photosynthesis, NO3/PO4 uptake and its relationship to calcification. Also how is this different in NPS (non-photosynthetic coral)?

Below is some information I've gathered while looking into the subject. Please correct me if I'm wrong anywhere!
In general, symbiotic bacteria (zooxanthellae) undergo photosynthesis to provide nutrient assimilation to the coral. The coral then uses the energy to do normal coral processes like respiration, mucus production, calcification. Image below found here

There's two components to a photosynthetic coral from what I understand in this paper (figure below)
1) Symbiotic polyps containing zooxanthellae (photosynthesis and calcification)
2) Asymbiotic polyps (calcification)

A potential mechanism is shown below. Red lines show the pathway in symbiotic polyps (photosynthesis). Black lines show the pathway for both symbiotic and asymbiotic polyps for calcification. In calcification, CO2 is converted to DIC (dissolved inorganic carbon) which is then oxidized into Carbonate (CO3)2- and incorporated into the coral skeleton. This process also creates a pH gradient, pushing protons (H+) into seawater and raises internal pH of the coral.

This figure shows a deeper explanation of photosynthesis in zooxanthellae of the host coral.
It also explains what happens when there is an interruption to photosynthesis (such as from a sudden drop in NO3/PO4/nutrients, or an alkalinity spike - both of which cause coral starvation). This interruption is followed by an overproduction of reactive O2 species (ROS) that promote bleaching and expelling of the coral's zooxanthellae.

My questions are
1) How is NO3 / PO4 involved in photosynthesis? Is it rate limiting? Do zooxanthellae use it or does the coral body use it?

2) How do NPS corals use NO3 / PO4 if they lack zooxanthellae? Do they use it at all? Does it negatively impact NPS coral function?

3) What is the mechanism for cell respiration /calcification in NPS corals?

4) How do coral inflate themselves? Is it done with a solute gradient?
The diagrams show that coral use a pH gradient during calcification (higher pH inside tissue than surrounding seawater). Is pH the solute, or is there another solute that makes coral inflate, such as HCO3 or a component of salt water?

5) How does seawater pH (too acidic or too basic) affect photosynthesis/respiration and calcification?


Thanks and happy reefing!

 

[Tennyson]

bump

 

[redfishbluefish]

I can answer your NO3 / PO4 questions....

The nitrogen and phosphorus are used by all cells to build necessary components....such as amino acids or ATP (Adenosine triphosphate), just to mention two compounds that utilize N and P.

I'll have to look, but pretty sure Dr. Randy wrote a paper about coral biology. I'll look for it and if I find it, I'll add it here.

EDIT TO ADD:

Could only find this one...but I'm sure there is another, but can't find it.

The Chemical and Biochemical Mechanisms of Calcification

 

[nereefpat]

Tough questions for a fish tank message board . I can get you started.

1) How is NO3 / PO4 involved in photosynthesis? Is it rate limiting? Do zooxanthellae use it or does the coral body use it?

Photosynthesis itself doesn't have much to do with Nitrate or Phosphate. It's all about using energy (light) to combine CO2 and H2O to make sugars that a plant can use later for energy and growth. A chlorophyll pigment does have a tiny amount of N, but no P. The zooxanthellae do all the photosynthesis.

2) How do NPS corals use NO3 / PO4 if they lack zooxanthellae? Do they use it at all? Does it negatively impact NPS coral function?

I'm certainly not an expert on NPS corals...N and P are building blocks. They are required by all forms of life, and they make up certain percentages of a cell's weight. N is used to make protein, and P is used in cell membranes, for example. Think of them as fertilizer. NPS corals *probably* can use N and P from the water column, while they *probably* have to capture some from the food they eat (plankton?). Again, I know little about NPS corals, so i'm just commenting on N and P in general.

3) What is the mechanism for cell respiration /calcification in NPS corals?

Respiration is the reaction used to get the energy out of sugar so it can be used for growth, repair, etc. It uses oxygen and sugar to yield energy, CO2, and H2O. Think of it as the opposite of photosynthesis. NPS corals collect food, and respire for energy. Sun corals, for example, collect plankton and use the energy for growth, including building skeleton.

4) How do coral inflate themselves? Is it done with a solute gradient?
The diagrams show that coral use a pH gradient during calcification (higher pH inside tissue than surrounding seawater). Is pH the solute, or is there another solute that makes coral inflate, such as HCO3 or a component of salt water?

I don't know. I'd have to do some reading.

5) How does seawater pH (too acidic or too basic) affect photosynthesis/respiration and calcification?

Stony corals build skeletons from Ca and carbonate. Ca and carbonate are present and separate in seawater. Corals combine them by increasing the pH so that the two combine (is precipitate still the right word?). The higher to tank's pH already is, the less the coral has to increase it to combine Ca and carbonate. So coral growth should, theoretically, be faster at higher tank pH. Lower pH usually means more CO2, so I wouldn't be surprised if that has some effect on photosynthesis. Planted freshwater tanks certainly benefit from CO2 injection, but I would suspect that CO2 isn't limiting for photosynthesis in our reef tanks. Too high of pH can cause inorganic precipitation of Ca and carbonate, and too low of pH could cause breakdown of coral/sand/rock. But I think both of those situations are very rare in our tanks.

Hopefully that helps. I know I rambled a bit, and didn't really use any references. Please discuss further.

 

[Tennyson]

Thanks for the responses! I figured Reef2reef would be the best place to ask these questions that don't really have readily available answers. Also please feel free to discuss the topic / contribute aside from just my questions!


Generally I've learned that higher alkalinity (9 - 12 dKH) needs to be matched with higher NO3/PO4 - because increasing coral growth with alkalinity also increases the demand for nutrients to supply that growth.

In contrast, with ULNS systems, nutrients are barely detectable and alkalinity is proportionally lower (less than 8 dKH). Growth may be slower but coral are more colorful.


with that in mind, here's some follow ups and I think that might be it for me

1) Why are coral more colorful in ULNS compared to nutrient rich? Is it because the available NO3/PO4 are used to develop pigment/protein instead of growth?

2) What parameter swings cause coral the most shock (aside from salinity and temp)? Is it drops in NO3/PO4? Or rapid decline/increases in alkalinity? Lighting? pH?

3) Why do unstable parameters cause coral and our reef tanks so much trouble?

4 - from earlier) How do coral inflate themselves? Is it done with a solute gradient?
Is pH the solute, or is there another solute that makes coral inflate, such as HCO3 or a component of salt water?

5) Coral inflate during feeding and also during parameter shock. Are these all by different mechanisms?