Assessing the Impact of Inorganic Carbon Availability on Coral

A project undertaken at the University of Techonology, Sydney and supervised by Lucy Buxton and Peter Ralph

Project Outline
The oceans, covering more than two thirds of the Earth’s surface play a vital role in removing carbon dioxide (CO2) from the atmosphere. However the massive CO2 loads added to the atmosphere since the industrial revolution have disrupted this delicate balance, and are causing considerable chemical changes in surface waters. This has a two fold effect, 1) CO2 reacts with seawater and is causing acidification of surface waters 2) in turn this alters the balance of inorganic carbon (Ci) available to photosynthetic organisms in the photic zone.

CO2 is already recognised as a major greenhouse gas and clear causal links have now been drawn between atmospheric CO2 and increases to global mean temperatures. Acidification of marine waters is an additional concern to that of global warming. And while global warming and resulting climate change has received considerable political, social, and scientific attention in recent years, the threat that acidification poses to marine flora and fauna has only recently been highlighted.

Sea surface acidification is predicted to occur most in warm shallow areas of low surface mixing, therefore making coral reefs and reef lagoons a prime target for localised acidification. Coral reefs are already at risk from temperature changes caused by global warming; the additional effects of changes in Ci availability and acidification have yet to be addressed. There is a vital need to incorporate the currently unknown effect of seawater acidification into the existing bleaching hypotheses.

This project focuses on the combined effects of dissolved carbon concentration, and temperature elevation on coral photosynthesis. Controlled experiments in the laboratory are combined with field measurements in order to produce environmentally relevant results. These studies will provide environmental managers with a more complete representation of environmental stresses occurring in Australian reef systems, and provide acidification researchers with valuable baseline data for further studies.

Fig. 1. Detail of symbiotic algal cells, zooxanthellae, which reside in the tissue of the coral host, and produce food for coral growth. The loss of zooxanthellae due to environmental stress is called coral bleaching (© L.Buxton)

Fig. 2. Coral colonies on the outer reef of Heron Island, Great Barrier Reef Marine Park (© L.Buxton)

Fig.3. Graph to show the correlation between rising atmospheric carbon dioxide concentrations and global mean temperatures (© Korte Organica)