Alkalinity Swing and Coral Mortality- Mechanism?

[andrewey]

For some reason, I'm struggling to find any write ups for the mechanism by which changes in alkalinity (and not the absolute level of alkalinity) are associated with coral mortality. I had assumed the mechanism involves the loss of carbonate/bicarbonate buffering against pH changes, but I'd love to know if this is accurate, if there are other mechanisms at play, or why the change in alkalinity within an acceptable range (7-11dkh) seems to play a significant role compared with the differences of absolute buffering capacity within this range.

Specifically, I am looking at mechanisms where alkalinity remains between 7-11dkh during the swing and where the pH remains appropriate (e.g. ~pH 8.2). For the purposes of this question, I would like to avoid the example of the association between ULNS systems and high alkalinity.

If anyone could point me in the right direction, I'd be very grateful! Thanks!

 

[Randy Holmes-Farley]

Mechanism is incredibly hard to scientifically prove.

My expectation is that corals develop a certain number of protein transporters in their cell membranes to uptake bicarbonate, and a sudden change in the available bicarbonate averaged over some period of time that is faster than the coral can adapt will flood the coral with bicarbonate, or starve it of bicarbonate, causing detrimental issues with calcification (from lack of or excess of carbonate from the bicarbonate) and photosynthesis (from lack of or excess of CO2 from the bicarbonate), and perhaps other processes (like internal pH control as the coral tries to make both CO2 and carbonate from the bicarbonate).

 

[nomsmon]

Mechanism is incredibly hard to scientifically prove.

My expectation is that corals develop a certain number of protein transporters in their cell membranes to uptake bicarbonate, and a sudden change in the available bicarbonate averaged over some period of time that is faster than the coral can adapt will flood the coral with bicarbonate, or starve it of bicarbonate, causing detrimental issues with calcification (from lack of or excess of carbonate from the bicarbonate) and photosynthesis (from lack of or excess of CO2 from the bicarbonate), and perhaps other processes (like internal pH control as the coral tries to make both CO2 and carbonate from the bicarbonate).

Chemistry is not my strong suite and buffers are a bit over my head so apologies for any errors.

If alkalinity changes without the pH changing does that mean one side of the carbonate buffer equilibrium has changed?
Alkalinity goes down, additional H+ has been added?
Alkalinity goes up, additional HCO2- or HCO3- has been added?

Are the coral uptaking HCO(2/3)- and Ca+ in ionic form? CaCO2 is insoluble in water right?

When additional H+ ions are added does this increase the amount of Ca2+ and HCO3- in the solution? Which seems like it would be beneficial to the coral. Does this shift the ratios of HCO3 to HCO2 as no H+ are released by the CaCO2 => Ca2 + 2HCO3 reaction?