Assessing the impacts of ocean acidification, global warming and terrestrial runoff on the cross-shelf variability of coral calcification in the central Great Barrier Reef

• Main Author: D'Olivo Cordero, Juan Pablo
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Subjects: coral calcification; ocean acidification; Great Barrier Reef; boron isotopes; Ocean acidification
• Online Access: http://hdl.handle.net/1885/11981; https://doi.org/10.25911/5d7391cc3ec1a; https://openresearch-repository.anu.edu.au/bitstream/1885/11981/6/DOlivo_J.P._2013.pdf.jpg

Ocean acidification and thermal stress due to anthropogenic greenhouse gas emissions present significant, potentially interacting, threats to the future of coral reefs. Coastal reef environments, as in the case of the Great Barrier Reef (GBR), can also be exposed to terrestrial stressors. This thesis evaluates the combined effects of ocean acidification, rising temperatures and river inputs on the calcification of Porites corals along a transect across-shelf the central GBR, north of Townsville. Calcification rates were obtained for 41 long-lived Porites corals from 7 reefs, in an inshore to offshore transect across the central GBR. The boron isotope composition (d11B) of selected cores was used to reconstruct annual and sub-annual changes in seawater pH in inner-shelf and mid-shelf environments. These unique seawater pH records are integrated with sea-surface temperature, river discharge and rainfall records to assess the nature and cause of seasonal, interannual, decadal and long-term (̃50 years) trends in coral calcification. Significant across-shelf differences in the temporal variability and long-term evolution of coral calcification are documented and can be related to local and global-scale changes in environmental conditions and water quality. Corals in the mid-shelf and outer-reef regions of the GBR exhibit an increase in calcification of 10.9% (1.1% S.E.) and 11.1% (3.9% S.E.) respectively since ̃1950 which are associated to the rise in sea-surface temperatures. However, calcification rates of mid-shelf corals show a decline of 3.3% (0.9% S.E.) over the recent period (1990-2008). This may indicate that a thermal optimum for calcification has been reached. Calcification rates in inner-shelf reefs over 1930-2008 display a long term trend of decreasing calcification of 4.6% (1.3% S.E.). The interannual-decadal component of variation is modulated by wet and dry periods, particularly during the last ̃40 years. The negative effects of bleaching on coral growth are evident in inshore reefs, and are ...