Concluding Thoughts

Over the past three months this blog has attempted to uncover some of the most significant climate related threats to coral reefs.  These are presented in the poster below (click to view full size). 




 

This exercise has revealed the fragile nature of these globally important marine ecosystems, as well as the potential loss in natural and economic wealth that a changing climate could bring about. It is evident that anthropogenic carbon dioxide emissions are creating conditions that test the resilience of coral reefs, due to the impact of increasing sea temperatures, acidifying oceans, rising sea levels and increasing storm intensity. Although it is apparent that coral reefs have adapted to dynamic climate conditions for thousands of years, the speed of contemporary climate change combined with direct human pressures poses a worrying threat. In order to ensure that the natural resilience of coral reefs enables these ecosystems to adapt to a changing climate it is imperative that detrimental human activities, such as overfishing, coral mining and sedimentation, are effectively managed. Ensuring that an effective balance between conservation practices and sustainable resource use for local people is met will help to maintain these ecosystems. As well as attempting to mitigate the effects of anthropogenic climate change, efforts need to be made to stop the problem at source. This means stricter and better enforced international policies to reduce anthropogenic environmental degradation, as well as investment in renewable energy sources and more efficient technologies. Ultimately, the future of coral reefs is in our hands, as is the case with many other important habitats. Being able to protect these ecosystems and prevent widespread extinctions is, in my mind, the most demanding challenge human’s face.

Tropical Storms, Climate Change and Reef Resilience

The increasing number, duration and intensity of tropical storms in response to a warming climate is another possible threat to coral reef ecosystems. This issue has only been discussed briefly in this blog, and since tropical storms have the potential to cause widespread damage to coral reefs it is a threat that should be examined. While coral reefs act as protection for coastal settlements, they can often be severely damaged during tropical storms. Global Circulation Models predict rising global average sea surface temperatures, increasing the likelihood of tropical storms (IPCC, 2007). Recovery from tropical storm damage can take many years, depending on the resilience of the reef. While the prediction of future changes to storm intensity inevitably involves uncertainty, data from the last thirty yeas suggests that the number of intense storms is increasing (Figure 1).




Figure 1: Total number of intense hurricanes, showing a significant increase in category four and five storms over the period 1970-2004 (Webster et al, 2005).




The assessment of coral damage following hurricanes and cyclones has been carried out for many years. Rogers et al (1991) monitored coral reef off the south coast of St John, US Virgin Islands, at a depth of 11-13m. Nine months after permanent transects were set up Hurricane Hugo struck, allowing the analysis of storm destruction. The category 5 hurricane caused patchy damage to the reef, with large waves moving and damaging significant quantities of coral and depositing sediment on the sea floor. Following the storm there was a decrease in the percentage of living coral by 40%, 12 months later there had been no significant increase in the amount of live coral. There was also a decline in species diversity following the storm. The ability of a coral reef to recover following storm damage is highly influenced by the extent of human activities, with overfished ecosystems showing poor recovery compared with less disturbed reefs. Similar results were found in a more recent study by Guillemot et al (2010), following Cyclone Erica in New Caledonia, South Pacific, 2003. The cover of live coral decreased by 45% in the two year period following this storm. After four years the coral reef displayed good signs of recovery, with a return to pre-cyclone fish community. It is suggested that the moderate anthropogenic pressure in this region was conducive to good resilience and recovery.




In order to predict how future changes in tropical storm intensity are likely to affect coral reef ecosystems it is useful to assess long-term variability as well as their role in ecosystem disturbances. Through topographical surveys and geological dating of coral ridges and terraces (which are produced by storms) it is possible to estimate historic storm surge and wave heights. Nott and Hayne (2001) determine the intensity of tropical cyclones along the Great Barrier Reef over the past 5,000 years using this method. Their results indicate a long history of intense tropical cyclones in this region, with the majority leading to widespread coral damage, including a weakening of the substrate which enables severe damage to occur during less intense storms. This study suggests that storm events are central to coral community structure and function, including the life span of individual corals. Therefore, if the frequency and intensity of these events is to change it may have significant negative repercussions for coral reef ecosystems. The authors of this study consequently believe that coral reef ‘vulnerability, exposure and risk is much higher than previously estimated’ (Nott and Hayne, 2001 p.511).




Once again it appears that coral reefs are likely to be negatively affected by climate change. Although there is strong evidence that coral reefs are resilient to storm damage, and are able to recover in the long-term, the ability of these ecosystems to do so is significantly reduced in regions where human pressures are having damaging impacts. The need to reinforce reef resilience through effective policies and management appears a necessity if these fragile, yet globally important, habitats are to be maintained.

In the news this week . . .

There is talk of extending the network of Australian Marine Protected Areas in order to prevent commercial fishing in a region of the Coral Sea. There is debate over whether a no-take MPA would be more economically viable than a multiple use MPA, due to the cost involved with enforcement and the loss of income for local people, compared with the potential environmental benefits that would occur with full protection. This issue links in nicely with this week’s post which looked at the economic valuation of nature, and the potential cost of climate change. The full news article can be viewed here.




This week scientists from around the world travelled to Belize for a conference, hosted by the Intergovernmental Panel on Climate Change and the Caribbean Community Climate Change Centre, aimed at discussing the impact of climate change on small nation islands. These nations are likely to be some of the worst affected by climate change, due to their dependence on fragile ecosystems, such as coral reefs. Sea level rise is also a very real threat to these regions, with potential impacts including a reduction in island size, a reduction in the level of freshwater and increased soil salinity. In order for their survival adaptation is a necessity, and workshops like these will help focus scientific investigation and international action on these issues.




Finally, here is a first-hand account of the damage that both human exploitation and climate change are doing to coral reefs in Bora Bora, French Polynesia. Provided by Jon Bowermaster, a National Geographic journalist, the article offers a fascinating insight into some of the main concerns in this region, as well as some interesting solutions.