Acropora phosphate paradox

[Miami Reef]

How can phosphate 0.10ppm or higher help acropora grow faster if it also inhibits calcification?

 

[Lavey29]

What exactly is fast acro growth?

 

[Miami Reef]

Look at the contradicting forum posts I found. Not found in the same thread.

Being that po4 is probably the least usable form of phosphorous form most organisms and is not preferred over meta/poly phosphates and particulate organic matter containing phosphorous, then I am not sure what the benefit is. po4 is a waste product in most systems.

I don’t think there’s any evidence about organic phosphate being more usable, or even as usable as inorganic phosphate.

 

[Miami Reef]

What exactly is fast acro growth?

Let’s say, for example, winning an acropora grow-out competition. What is most optimal?

Acropora need phosphorus/phosphate, but inorganic phosphate can inhibit calcification.

 

[taricha]

There was a paper that gets discussed around here a decent amount that at least resolves your paradox. Under higher Phosphate, the coral grew faster but the calcification was less dense.
Effects of phosphate on growth and skeletal density in the scleractinian coral Acropora muricata: A controlled experimental approach

"Acropora muricata were sub-divided and distributed among three 110-L aquaria, and exposed to phosphate levels of 0.09, 0.20, and 0.50 mg L− 1 for four months. Total skeletal length, living tissue length, weight, branch production, and polyp extension were measured. Linear extension and tissue growth increased under all conditions. Growth rates were highest at a phosphate concentration of 0.50 mg L− 1. Weight increased through time, graded from low to high with phosphate concentration. Density decreased through time, and was significantly lowest in the high phosphate treatment. Phosphate concentration produced no visible effects of stress on the corals, as indicated by polyp extension and lack of mortality. It is suggested that the phosphate enhanced growth was due to increased zooxanthellar populations and photosynthetic production within the coral. Skeletal density reduction may be due to phosphate binding at the calcifying surface and the creation of a porous and structurally weaker calcium carbonate/calcium phosphate skeleton. Increased phosphate concentrations, often characteristic of eutrophic conditions, caused increased coral growth but also a more brittle skeleton."

For a hypothetical grow-out contest you don't care about skeletal density, you'd want weight and linear growth from higher PO4.
For long term health, you might want something different - or maybe not. That wasn't evaluated in the paper.

 

[Miami Reef]

There was a paper that gets discussed around here a decent amount that at least resolves your paradox. Under higher Phosphate, the coral grew faster but the calcification was less dense.
Effects of phosphate on growth and skeletal density in the scleractinian coral Acropora muricata: A controlled experimental approach

"Acropora muricata were sub-divided and distributed among three 110-L aquaria, and exposed to phosphate levels of 0.09, 0.20, and 0.50 mg L− 1 for four months. Total skeletal length, living tissue length, weight, branch production, and polyp extension were measured. Linear extension and tissue growth increased under all conditions. Growth rates were highest at a phosphate concentration of 0.50 mg L− 1. Weight increased through time, graded from low to high with phosphate concentration. Density decreased through time, and was significantly lowest in the high phosphate treatment. Phosphate concentration produced no visible effects of stress on the corals, as indicated by polyp extension and lack of mortality. It is suggested that the phosphate enhanced growth was due to increased zooxanthellar populations and photosynthetic production within the coral. Skeletal density reduction may be due to phosphate binding at the calcifying surface and the creation of a porous and structurally weaker calcium carbonate/calcium phosphate skeleton. Increased phosphate concentrations, often characteristic of eutrophic conditions, caused increased coral growth but also a more brittle skeleton."

For a hypothetical grow-out contest you don't care about skeletal density, you'd want weight and linear growth from higher PO4.
For long term health, you might want something different - or maybe not. That wasn't evaluated in the paper.

Thank you very much.

What about nitrate levels? Do higher levels slow or increase growth? I read conflicting opinions and I want to know what the papers say.

 

[taricha]

What about nitrate levels? Do higher levels slow or increase growth? I read conflicting opinions and I want to know what the papers say.

There's papers that show high nitrate can be harmful if it's paired with low phosphate values, but not necessarily harmful if other nutrients are available in excess along with nitrate.
If you're looking for optimal, very few would argue that published research shows nitrate is optimal as a nitrogen source, it's used because it's stable, common, and easy.
Other N sources are almost universally preferred, but it's hard to regulate the amount of stuff like ammonia and amino acids, and particulate foods in the water.
So I'd argue for some level of NO3 to remain in the water as an N-source of last resort if the other N-sources are consumed.

 

[taricha]

I should add that I optimal coral nutrition for SPS is way outside my comfort zone of topics.
There are people with decades of practical experience and their advice should be given more weight than somebody like me who reads some papers.

 

[Randy Holmes-Farley Verified Community Expert]

Faster growth is always relative to something else. If compared to levels too low, higher phosphate will accelerate growth.

I’d also caution that there’s a lot of conflicting info that may relate to what other sources and levels of N and P are available, as well as different effects on different organisms.

 

[areefer01]

There was a paper that gets discussed around here a decent amount that at least resolves your paradox. Under higher Phosphate, the coral grew faster but the calcification was less dense.
Effects of phosphate on growth and skeletal density in the scleractinian coral Acropora muricata: A controlled experimental approach

Didn't BRS have a video or something trying to show coral growth over time vs a parameter? Maybe it was pH and I'm mixing it up with phosphate. I'm at 2.2 ppm and haven't noticed any slowdown.

Edit: I also meant to add that I don't believe the corals are any less fragile. I do not frag but they are not brittle to touch (like trying to snap off a piece with my fingers vs. tool).

 

[taricha]

Edit: I also meant to add that I don't believe the corals are any less fragile. I do not frag but they are not brittle to touch (like trying to snap off a piece with my fingers vs. tool).

Right. Even if skeletal density decreases 30%, we probably don't care in an aquarium context - unless those conditions involved some other more relevant weakness of the coral.
The "storms" in our tanks are pretty mild.