Assessing ocean acidification impacts on the reef building properties of crustose coralline algae
Crustose coralline algae (CCA), and in particular Porolithon onkodes, play an important reef-building role in modern tropical coral reefs. CCA form thick crusts of Mg-calcite and grow over corals and loose substrate to bind these together. This binding and cementing process is fundamental to the dev...
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| Format: | Doctoral or Postdoctoral Thesis |
| Language: | English |
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| Online Access: | http://hdl.handle.net/1885/110700 https://doi.org/10.25911/5d7635dc4e712 https://openresearch-repository.anu.edu.au/bitstream/1885/110700/4/Nash%20Thesis%202016.pdf.jpg |
| Summary: | Crustose coralline algae (CCA), and in particular Porolithon onkodes, play an important reef-building role in modern tropical coral reefs. CCA form thick crusts of Mg-calcite and grow over corals and loose substrate to bind these together. This binding and cementing process is fundamental to the development of structural reefs that are capable of withstanding the high-energy waves in the shallow to inter-tidal areas of the reef. As anthropogenic CO2 emissions continue to increase, the oceans absorb part of this extra CO2 and become more acidic, a process known as Ocean Acidification (OA). There are concerns that OA will have a negative affect on the reef-building capacity of coral reef organisms, in particular on CCA. This is because Mg-calcite is meta-stable and more susceptible to dissolution than aragonite, the mineral used by corals to build skeletons. The goal of this thesis work was to firstly understand the physical and mechanical properties that enable the CCA to cement the reef and withstand damage from high-energy waves, bioerosion and chemical dissolution. Secondly, to anticipate how OA may interfere with these reef-building properties. These goals were pursued by setting clear aims with associated specific objectives designed to elucidate information relevant to these questions. Methods were developed for X-ray diffraction to identify the mineral composition of CCA. Nanoindentation was investigated as a tool for determining the mechanical properties of CCA and the measurement of fracture toughness was found to return physically meaningful information relevant to structural reef development. Study of CCA calcification showed that cell wall Mg-calcite exhibited radial crystal morphology in agreement with published studies on temperate species. However, high-resolution imaging showed the radial crystals were made of banded stacked sub-micron grains within an organic framework. Dolomite was found not only as cell lining by submicron rhombs, but also as the primary calcification of hypothallial cell ... |
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