Figure 6. Calcification and pH_i regulation in C. pelagicus.

(A) Calcification rate following manipulation of pH_i. Coccolith production by decalcified C. pelagicus cells in f/2 FSW media (pH 8.2, 15 °C) was monitored by cross-polarised light microscopy (upper right and Figure S6). Upper left shows a scanning electron micrograph of a C. pelagicus cell with an intact coccosphere for reference. Scale bars, 10 µm. pH_i was manipulated by perfusion with f/2 media at pH 8.2 (control), at pH 6.5, or at pH 8.2 + 10 mM NH₄Cl for 10 min (lower panel). Note the appreciable lag in restoration of the initial calcification rate following acidification of the cytosol. Traces are normalized to initial rate (0–150 min). (B) Mean calcification rate (±SE) was calculated by linear regression for each period (0–150, 150–300, and 300–600 min) and is expressed as a percentage of the initial rate (n = 4 except for pH 6.5, where n = 3).