New Paper: holding coral reefs together
Assisted by AI
Our study takes a detailed look at the processes that form and maintain ‘algal ridge’ structures around the coral reef at One Tree Island, Australia. Algal ridges are crucial for the existence of coral reefs. They form elevated barriers on the windward sides of reefs, breaking up wave energy and protecting the calmer, more delicate areas behind them. Their existence depends on biogoechemical processes that ‘cement’ the ridges together. Our study delves into those biogeochemical processes.
We discovered that the ridge’s subsurface is predominantly anoxic. We found hydrogen sulphide present in the water, indicating active sulphate-reducing bacteria. These bacteria play a pivotal role in driving the carbonate precipitation that cements the subsurface of the ridge together.
One of our key findings is that the total alkalinity (TA) and pH levels in the ridge’s porewater are primarily influenced by anoxic respiration processes, especially those driven by sulphate-reducing bacteria. However, the TA levels in the porewater are lower than in the surrounding seawater, as more TA is consumed through carbonate precipitation than is generated by these processes. This highlights a delicate balance between carbonate precipitation and dissolution within the algal ridge, a dynamic that is crucial for its structural integrity.
Our study challenges the traditional view that diagenetic processes in high-energy reef systems are driven mainly by the pumping of oxygenated seawater due to wave action. Instead, we propose that these processes can also occur under anoxic conditions, driven by geochemical changes induced by sulphate-reducing bacteria. This revelation shifts our understanding of how these ridges are formed and maintained, particularly under the influence of complex microbial activities.
This study provides new insights into the role of sulphate reduction and carbonate precipitation in the formation and maintenance of algal ridges under anoxic conditions. Understanding these processes is crucial for predicting how these vital reef structures will respond to future environmental changes, particularly as they face the dual threats of ocean acidification and other anthropogenic impacts. The resilience of coral reefs may depend significantly on the continued function and stability of these algal ridges.