How can phosphate 0.10ppm or higher help acropora grow faster if it also inhibits calcification?
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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.
Let’s say, for example, winning an acropora grow-out competition. What is most optimal?What exactly is fast acro growth?
Thank you very much.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.
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 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
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.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).