• carbon acquisition mechanisms
• calcification
• C.elongata
• C. officinalis
• anion exchanger
• carbonic anhydrase

Bicarbonate is the most abundant form of inorganic carbon in seawater and it has been already established that algae use this form of inorganic carbon to perform photosynthesis but it’s not very clear if this form is also used for the calcification process as well.

The currently-accepted hypothesis that biological calcification rates are a simple function of seawater CaCO3 saturation state was tested experimentally. The results from Corallina officinalis show that, calcification is far more responsive to changes in inorganic carbon than to calcium concentrations; and when [CO3-] is kept constant, increases in [HCO3-] cause dramatic increases in calcification rates, even at reduced pH.
All these data suggest that calcification in Corallina officinalis is a biologically controlled process, influenced mainly by the bicarbonate and pH but also mediated by light and nitrogen.


The presence of the two main bicarbonate transporters, carbonic anhydrase (CA) and anion exchanger (AE) like transport protein was investigated using the inhibitors Acetazolamide (AZ) and 6-Ethoxy-2-benzothiazole-sulfonamide (EZ) for CA and 4-Acetamino-4isithiocyanato 2,2’-stibene disulfonic acid disodium salt hydrate (SITS) and 4,4-Diisothiocyanatostilbene-2,2’-disulfonic acid (DIDS) for AE. The results showed that CA is the main carbon acquisition mechanism and that AE protein is only present in Corallina elongata and its activity disappear during summer time.
The anion exchanger protein (AE) was also localized with immunostaining. AE is located around the medulla, in the cortex and mostly in the genicula.

This study also examined how the carbon acquisition mechanisms are influenced by the environment. Nitrate inhibition was shown to be a strong inhibitor of calcification specially during the night, depending on the nitrate concentration in the environment.
The competition between bicarbonate and nitrate is demonstrated to be the reason for the inhibition, is still have to be explained why only calcification is affected. This inhibition is temporary, there is an instantaneous recovery of the organism once is out of the high nitrate environment, this can have a lot of implication for the waste water management.