Dolomite-rich coralline algae in reefs resist dissolution in acidified conditions

• Main Authors: Nash, Merinda C, Opdyke, Bradley N, Troitzsch, U, Russell, Bayden D, Adey, W H, Kato, A, Diaz-Pulido, Guillermo, Brent, C, Gardner, M, Prichard, J, Kline, David I
• Format: Dataset
• Language: English
• Published: PANGAEA 2013
• Subjects: Alkalinity; total; Aragonite; Aragonite saturation state; Benthos; Bicarbonate ion; Bottles or small containers/Aquaria (<20 L); Calcification/Dissolution; Calcite saturation state; Calculated using CO2SYS; Calculated using seacarb after Nisumaa et al. (2010); Carbon; inorganic; dissolved; Carbonate ion; Carbonate system computation flag; Carbon dioxide; Coast and continental shelf; Fugacity of carbon dioxide (water) at sea surface temperature (wet air); Group; Laboratory experiment; Macroalgae; Magnesium carbonate; magnesite; OA-ICC; Ocean Acidification International Coordination Centre; Partial pressure of carbon dioxide (water) at sea surface temperature (wet air); pH; Plantae; Porolithon onkodes; Potentiometric; Potentiometric titration; Replicate; Rhodophyta; Salinity; Sample code/label; Single species; South Pacific; Species; Temperate; Temperature; water; Treatment; Weight loss; Ocean acidification
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.825092; https://doi.org/10.1594/PANGAEA.825092

Coral reef ecosystems develop best in high-flow environments but their fragile frameworks are also vulnerable to high wave energy. Wave-resistant algal rims, predominantly made up of the crustose coralline algae (CCA) Porolithon onkodes and P. pachydermum, are therefore critical structural elements for the survival of many shallow coral reefs. Concerns are growing about the susceptibility of CCA to ocean acidification because CCA Mg-calcite skeletons are more susceptible to dissolution under low pH conditions than coral aragonite skeletons. However, the recent discovery of dolomite (Mg0.5Ca0.5(CO3)), a stable carbonate, in P. onkodes cells necessitates a reappraisal of the impacts of ocean acidification on these CCA. Here we show, using a dissolution experiment, that dried dolomite-rich CCA have 6-10 times lower rates of dissolution than predominantly Mg-calcite CCA in both high-CO2 (~ 700 ppm) and control (~ 380 ppm) environments, respectively. We reveal this stabilizing mechanism to be a combination of reduced porosity due to dolomite infilling and selective dissolution of other carbonate minerals. Physical break-up proceeds by dissolution of Mg-calcite walls until the dolomitized cell eventually drops out intact. Dolomite-rich CCA frameworks are common in shallow coral reefs globally and our results suggest that it is likely that they will continue to provide protection and stability for coral reef frameworks as CO2 rises.