So the suggestion is that there is aspartic acid, or aspartic acid-containing proteins, that absorb onto both biological and abiotic CaCO3.
Yes.
Still, I'm not sure this type of data bears on whether aspartic acid concentrations might be limiting or not to the growth of a coral, does it?
Not the given data.
Biological deposited minerals go hand in hand with a organic matrix. E.g the organics associated with silicate depositing organisms such as organic coating of diatoms and sponge spicules contain relatively more serine, threonine and glycine compared to cell contents or tissue.
Serine and threonine (both hydroxyl containing) are likely candidates for Si4+ coordination. (Off topic: would they be adsorbed on glass?, could this cause diatom growth on glass?)
The primary structure of many proteins regularly reveals serine successions: Ser-Ser , Ser-Ser-Ser, Ser-X-Ser , Ser-X-Y-Ser.
Some poteolytic and esterase enzymes have serine at the active center and threonine next to the active site. In an aorta tissue this ability is sometimnes a disadvantage for the organism since formation of silicates can be initiated.
A lot of research is going on on organic matrices in all sorts of organisms and there is indirect proof that the organic matrix is essential for bio-mineralisation. If this is true then that could be rate determining for skeletogenesis.
It is also believed/speculated that the realtive proportion of amino acids with respect to each other and the sequence determines which crystal structure is deposited.
There are also proteins in corals which inhibit CaCO3 crystallisation. E.g. the mucus of Galaxea fascicularis and some of its water soluble organic macromolecules (extracted with water from exoskelton) inhibit CaCO3 crystallisation (In vitro!).
This prevents CaCO3 deposition on the outside of the coral tissue. This might have been of importance millions of years ago when the oceans were far more saturated with respect to CaCO3.
When I try to picture the skeleton of corals over simplified in my mind I see spherulitic CaCO3 with inbetween the organic matrix. The organic matrix ensures a coherent structure can possibly give some elasticity allows absorbtion of mechanical energy and ensures that the surface is not poisoned by CaCO3 inhibiters.
I also see at it (over simplified in my mind) as a polymeric fiber. Crystalline and amorphous regions in which crystals and amorphous parts are conected by polymer chains emerging from other crystalline and amorphous parts.
It is impossible to think that coral skeleton or human bones are composed of singel crystals. Even without knowing e.g. Avrami equations for crystallisation, it is safe to assume that even under the most favourable condition the crystal size will be finite and probably be less than say a few tenths of a millimeter.
So something will be needed to bond the crystals together. A glue such as the organic matrix is very likely. Especially because the organic matrix of corals contains relatively large amount of acidic amino acids such as aspartic acid which have a high binding affinity with CaCO3 and are at least bi-functional.
Note: A few parts of this message have been cited without giving references.
For fun:
3 most abundant amino acids (resd/1000) in;
Human bone: glycine 319, proline 123, alanine 114
Human dentin: glycine 319, proline 115 , alanine 112
Human enamel(developing): proline 251, glutamic acid 142 , leucine 91
Human enamel (mature) : glycine 193 , proline 137 , serine 119