Ocean acidification does not affect magnesium composition or dolomite formation in living crustose coralline algae, <i>Porolithon onkodes</i> in an experimental system
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 <i>p</i>CO<sub>2</sub> and ocean acidification. Due to the higher solubility of Mg-calcite, i...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-09-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/12/5247/2015/bg-12-5247-2015.pdf |
| Summary: | 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 <i>p</i>CO<sub>2</sub> 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 <i>Porolithon onkodes</i>, the predominant
encrusting species on tropical reefs, can have dolomite
(Ca<sub>0.5</sub>Mg<sub>0.5</sub>CO<sub>3</sub>) infilling cell spaces which increases their
stability. However, nothing is known about how bio-mineralised dolomite
formation responds to higher <i>p</i>CO<sub>2</sub>. Using <i>P. onkodes</i> grown for
3 and 6 months in tank experiments, we aimed to determine (1) if mol %
MgCO<sub>3</sub> in new crust and new settlement was affected by increasing
CO<sub>2</sub> 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<sub>2</sub>. Our results show that there was no
significant effect of CO<sub>2</sub> on mol % MgCO<sub>3</sub> 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<sub>2</sub> treatment.
While evidence mounts that climate change will impact many sensitive coral
and CCA species, the results from this study indicate that reef-building
<i>P. onkodes</i> will continue to form stabilising dolomite infill under
near-future acidification conditions, thereby retaining its higher resistance
to dissolution. |
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| ISSN: | 1726-4170 1726-4189 |