Figure 2: Influence of photosynthetic algal tissue and pCO2 and temperature on carbonate mineralogy.

Photosynthetically active tissue (surface layer) governs the mineralogical response (that is, dolomite (a), aragonite (b) or MgCO3 (c)) of crustose coralline algae when exposed to pre-industrial (Pre), control (Cont) and High pCO2 concentrations and ambient (28 °C, blue bars) and warming (30 °C, red bars) temperatures. (a) Total asymmetry as an indicator of dolomite amount is higher in bulk tissue (ANOVA, P<0.001, n=3) than the surface layer and asymmetry increased under greenhouse conditions (high pCO2 and 30 °C) only in bulk samples (P<0.001, n=3). (b) Aragonite % is higher in bulk samples (P<0.001, n=3) and under pre-industrial pCO2 and ambient temperature (28 °C) (P=0.001, n=3). Negligible amounts were found in greenhouse surface layer samples. (c) High- MgCO3 (mol% MgCO3) has less Mg-content in surface layers (P<0.001) than in the bulk tissue, but an increase in surface layers is observed under warming conditions (P=0.004, n=3). Data are presented as means and error bars denote s.e.m.