Ocean acidification does not affect magnesium composition or dolomite formation in living crustose coralline algae, Porolithon onkodes in an experimental system

• Published in: Biogeosciences
• Main Authors: M. C. Nash, S. Uthicke, A. P. Negri, N. E. Cantin
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2015
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; Ocean acidification
• Online Access: https://doi.org/10.5194/bg-12-5247-2015; https://doaj.org/article/9d8a6fb1505b48dbac44a42790d149b9

There are concerns that Mg-calcite crustose coralline algae (CCA), which are key reef builders on coral reefs, will be most susceptible to increased rates of dissolution under higher p CO 2 and ocean acidification. Due to the higher solubility of Mg-calcite, it has been hypothesised that magnesium concentrations in CCA Mg-calcite will decrease as the ocean acidifies, and that this decrease will make their skeletons more chemically stable. In addition to Mg-calcite, CCA Porolithon onkodes , the predominant encrusting species on tropical reefs, can have dolomite (Ca 0.5 Mg 0.5 CO 3 ) infilling cell spaces which increases their stability. However, nothing is known about how bio-mineralised dolomite formation responds to higher p CO 2 . Using P. onkodes grown for 3 and 6 months in tank experiments, we aimed to determine (1) if mol % MgCO 3 in new crust and new settlement was affected by increasing CO 2 levels (365, 444, 676 and 904 μatm), (2) whether bio-mineralised dolomite formed within these time frames, and (3) if so, whether this was effected by CO 2 . Our results show that there was no significant effect of CO 2 on mol % MgCO 3 in any sample set, indicating an absence of a plastic response under a wide range of experimental conditions. Dolomite within the CCA cells formed within 3 months and dolomite abundance did not vary significantly with CO 2 treatment. While evidence mounts that climate change will impact many sensitive coral and CCA species, the results from this study indicate that reef-building P. onkodes will continue to form stabilising dolomite infill under near-future acidification conditions, thereby retaining its higher resistance to dissolution.