Overview of Coral Reefs and the Threats Posed by a Changing Climate

Coral reefs have a high ecological importance, due to their biodiversity and the provision of a wide range of ecosystem services that are required by humans. They are often referred to as the 'Rainforests of the Sea', home to around 25% of marine species, while occupying only 1% of the ocean floor (Mulhall, 2009). Benefits to humans include: the provision of fish; coastal protection from storms; the potential successful tourism industry; source of medicines. These ecosystem services are under threat from a combination of stressors that stem from both human exploitation and anthropogenic climate change.



The formation of corals is best explained by this informative video:



The threats to coral reefs from climate change result from a combination of stresses including: increasing sea surface temperatures; sea level rise; ocean acidification due to increased atmospheric carbon dioxide concentration; changing salinity; altered ocean currents; more intense storms through ENSO variation. The impact of ENSO variation has been highlighted by recent tropical storms in north-east Australia, causing damage and sedimentation. The vast size of this cyclone is portrayed here, indicating the area of reef that was affected.



Over the next few weeks each of these threats will be discussed in detail, they are outlined in this video featuring Ove Hoegh-Guldberg, whose paper was discussed in the post below and who runs a blog that contains a wealth of information regarding climate change:

Understanding and predicting the impacts of climate change is a necessity in order to mitigate the impacts and attempt to preserve these important resources. Dr Barrie Pittock’s 1999 paper attempts to estimate changes to the environmental factors that affect coral reef ecosystems. Predicted changes include a 2-3°C increase in sea surface temperatures by the end of this century, sea level rise at a rate of 1-10mm per year and tropical cyclone intensity is expected to increase by 10-20% by 2070. These changes must then be translated into direct ecosystem consequences, such as potential species extinction. A recent attempt at predicting coral reef fish vulnerability from multiple stressors (including both climate driven habitat loss and the effects of fishing) was undertaken by Graham et al (2011). This study predicts that around a third of all coral reef fish species in the Indian Ocean are at risk from localised extinctions. Interestingly those species most at risk from one factor are not vulnerable to the other. This is worrying, as areas where both stressors are present will suffer greatly.

Figure 1  Vulnerability of coral reef fish species to fishing and climate driven habitat disturbances in Indian Ocean (Source: Graham et al, 2011). 




It is evident that anthropogenic climate change affects coral reef ecosystems significantly, through a variety of stressors. In order to be able to mitigate the impacts of a changing climate on coral reefs, preserving their biodiveristy and the provision of vital ecosystem services, the effective modelling of future changes is required.