Production and accumulation of reef framework by calcifying corals and macroalgae on a remote Indian Ocean cay
<p>Coral reefs face increasing pressures in response to unprecedented rates of environmental change at present. The coral reef physical framework is formed through the production of calcium carbonate (<span class="inline-formula">CaCO<sub>3</sub></span>) and m...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2023-03-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/20/1011/2023/bg-20-1011-2023.pdf |
| Summary: | <p>Coral reefs face increasing pressures in response to unprecedented rates of environmental change at present. The coral reef physical framework is
formed through the production of calcium carbonate (<span class="inline-formula">CaCO<sub>3</sub></span>) and maintained by marine organisms, primarily hermatypic corals, and calcifying algae. The northern part of Western Australia, known as the Kimberley, has largely escaped land-based anthropogenic impacts and this study provides important metabolic data on reef-building organisms from an undisturbed set of marine habitats. From the reef platform of Browse Island, located on the mid-shelf just inside the 200 <span class="inline-formula">m</span> isobath off the Kimberley coast, specimens of the dominant coral (six species) and algal (five species) taxa were collected and incubated ex situ in light and dark shipboard experimental mesocosms for 4 <span class="inline-formula">h</span> to measure rates of calcification and production patterns of oxygen. During experimental light and dark incubations, all algae were net autotrophic producing 6 to 111 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M4" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">mmol</mi><mspace linebreak="nobreak" width="0.125em"/><msub><mi mathvariant="normal">O</mi><mn mathvariant="normal">2</mn></msub><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">m</mi><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">d</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="82pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="d5faf179aedb03711a27d6fc8a92f85e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-20-1011-2023-ie00001.svg" width="82pt" height="16pt" src="bg-20-1011-2023-ie00001.png"/></svg:svg></span></span>. In contrast, most corals were net consumers of <span class="inline-formula">O<sub>2</sub></span> with average net fluxes ranging from <span class="inline-formula">−</span>42 to 47 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">mmol</mi><mspace width="0.125em" linebreak="nobreak"/><msub><mi mathvariant="normal">O</mi><mn mathvariant="normal">2</mn></msub><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">m</mi><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">d</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="82pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="4ced8ec024bcae4c4de1e6a495a21393"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-20-1011-2023-ie00002.svg" width="82pt" height="16pt" src="bg-20-1011-2023-ie00002.png"/></svg:svg></span></span>. The net change in pH was generally negative for corals and calcifying algae (<span class="inline-formula">−</span>0.01 to
<span class="inline-formula">−</span>0.08 <span class="inline-formula">h<sup>−1</sup></span>). Resulting net calcification rates (1.9 to 9.9 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">g</mi><mspace width="0.125em" linebreak="nobreak"/><msub><mi mathvariant="normal">CaCO</mi><mn mathvariant="normal">3</mn></msub><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">m</mi><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">d</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="83pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="9fd6f5b5523b408501bd3925892de3ba"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-20-1011-2023-ie00003.svg" width="83pt" height="16pt" src="bg-20-1011-2023-ie00003.png"/></svg:svg></span></span>) for corals and calcifying algae
(<i>Halimeda</i> and <i>Galaxura</i>) were all positive and were strongly correlated with net <span class="inline-formula">O<sub>2</sub></span> production. In intertidal habitats around Browse Island, estimated relative contributions of coral and <i>Halimeda</i> to the reef production of <span class="inline-formula">CaCO<sub>3</sub></span> were similar at around 600 to 840 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M14" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">g</mi><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">m</mi><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">yr</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="50pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="e28c3cb62a32cbeb793fafd4d3225939"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-20-1011-2023-ie00004.svg" width="50pt" height="15pt" src="bg-20-1011-2023-ie00004.png"/></svg:svg></span></span>. The low reef platform had very low coral cover of <span class="inline-formula"><</span> 3 % which made a smaller contribution to calcification of <span class="inline-formula">∼</span> 240 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M17" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">g</mi><mspace width="0.125em" linebreak="nobreak"/><msub><mi mathvariant="normal">CaCO</mi><mn mathvariant="normal">3</mn></msub><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">m</mi><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">yr</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="86pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="1cec03640aad7994849a3558001b9b3b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-20-1011-2023-ie00005.svg" width="86pt" height="16pt" src="bg-20-1011-2023-ie00005.png"/></svg:svg></span></span>. Calcification on the subtidal reef slope was predominantly from corals, producing
<span class="inline-formula">∼</span> 1540 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M19" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">g</mi><mspace linebreak="nobreak" width="0.125em"/><msub><mi mathvariant="normal">CaCO</mi><mn mathvariant="normal">3</mn></msub><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">m</mi><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">yr</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="86pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="4bd0deb57a0ecd2f11f30170b14104cf"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-20-1011-2023-ie00006.svg" width="86pt" height="16pt" src="bg-20-1011-2023-ie00006.png"/></svg:svg></span></span>, twice that of <i>Halimeda</i>. These data provide the first measures of community metabolism from the offshore reef systems of the Kimberley. The relative contributions of the main reef builders, in these undisturbed areas, to net community metabolism and <span class="inline-formula">CaCO<sub>3</sub></span> production is important to understand exclusively climate-driven negative effects on tropical reefs.</p> |
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| ISSN: | 1726-4170 1726-4189 |