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.

The Economic Cost of Climate Change

This blog has presented the major climate related threats to coral reef ecosystems. While the focus has primarily been on the ecological consequences, there are also important economic costs that should be taken into consideration. The economic costs associated with the impacts of climate change on coral reefs comprise both direct costs, such as lower incomes for fishers due to decreased fish populations, and indirect costs, such as the cost of decreased biodiversity and coastal protection. In many cases attaching an economic cost to an environmental issue has proved to be the catalyst for action, as it enables mechanisms to be established that incorporate the environmental cost into activities which have detrimental environmental impacts. Most of the literature regarding this issue examines the economic cost of direct human impacts, such as overfishing and tourism, rather than the potential cost of climate change. However, it is possible to get an understanding of the economic value which has been placed on coral reefs by examining studies that focus on human exploitation. From this it is possible to infer the potential economic cost of a changing climate.




A brief introduction on the subject of valuing nature is provided by Pavan Sukhdev, Special Advisor and Head of UNEP’s ‘Green Economy Initiative’:







A study by White et al (2000) investigates the economic losses caused by reef destruction in the Philippines. Here coral reef fisheries are worth around US$1billion per year, providing a living to around one million small-scale fishers. Coral reef damage in the Philippines is extensive, with less than 5% in ‘excellent’ condition. In Bacuit Bay, Palawan it has been estimated that fisheries and tourism would produce US$41 million more than forestry operations in the watershed (which is causing sedimentation in the bay) over a ten year period (Hodgson and Dixon, 1988). The rise in ecotourism in Bacuit Bay indicates the potential for the sustainable use of this resource, enabling both economic benefits as well as achieving conservation goals. The biodiversity and aesthetic value of Mabini, a marine sanctuary in the Philippines, is estimated at US$300,000 per year based on an average visitor’s willingness-to-pay for entrance. This paper highlights the potential economic cost of a changing climate, if it leads to ecosystem degradation, providing economic justification for coral reef management in this region.




The ‘environmental economics of coral reef destruction in Sri Lanka’ are considered by Berg et al (1998). The total quantifiable economic value of these reefs (which includes the fish-habitat function, the tourist-attraction function and the physical-structure function) is estimated at between US$13,000 – US$4,404,000km² annually. From this, the net economic cost of coal mining in highly developed areas over a 20 year period is estimated to amount to around US$6,615,000. Although climate related impacts may not be as severe as this activity, it provides evidence to support the view that investment should be made in order to mitigate the effects of a changing climate.




While many studies attempt to value coral reefs based on the potential income provided, Pendleton (1995) examines the economic benefits of a marine park based on what it would cost to provide the ecosystem services that the coral reef ecosystem currently supplies. It is estimated that the cost of operating Bonaire Marine Park in the Caribbean Islands to protect the reef would be around 0.7% of the net benefits. Evidently the potential cost of coral reef degradation far outweighs the cost of taking action, assuming that conservation is effective in preserving the reef.




As mentioned above, although these papers are useful in exploring the economic value of coral reef ecosystems, they are mainly concerned with estimating the cost of human exploitation. Brander et al (2009) explore the economic impact of ocean acidification on coral reefs. Their study examines reefs which are considered both economically and ecologically important, and models the cost attached to acidifying oceans based on the four IPCC emission scenarios. Figure 1 presents the estimated annual economic cost of coral reef loss in response to ocean acidification, indicating the escalating costs associated with this environmental issue. It is interesting to note that the B1 scenario is predicted to produce economic benefits by 2085. This is because the B1 scenario relates to an integrated and ecologically friendly world, which utilises clean, efficient technologies and relies on global solutions to provide environmental stability (IPCC, 2007).




Figure 1: Annual economic cost of ocean acidification induced coral reef loss, under four different emission scenarios (Brander et al, 2009).

These studies have emphasised the high economic value that is placed on coral reef ecosystems, and therefore highlight the potential economic cost that climate change (in conjunction with human resource exploitation) is likely to have. The economic justification for investment in conservation and mitigation projects is evident, and should provide motivation for global action.  

Reconstructing Past Climates

As demonstrated in my post on 4^th April, the investigation of fossilised reefs allows the reconstruction of historic sea level fluctuations. This is possible due to the known ecological conditions required by certain species of coral. Similarly, it is possible to investigate other aspects of climate, such as air temperature, sea surface temperature, precipitation and salinity, by using coral reefs as a palaeoclimate proxy indicator. Since the 1970s palaeo-climatologists have realised the potential of coral reefs to monitor climate variations. Coral growth rates, density bands and isotopic composition respond to changes in climate, and can therefore be used to reconstruct past climates (Dunbar and Wellington, 1981). Dunbar and Wellington’s paper assessed the stable oxygen isotopic response to seasonal changes in temperature, salinity and growth rate of branching corals. The coral was stained at certain points in time so that visible markers facilitated the measurement of growth rates and isotopic profiles. By measuring ocean temperature, salinity and oxygen isotopic composition of seawater over the period of a year it was possible to link these changes with observed variations in the coral composition and growth rate. They conclude that variations in oxygen isotopes in coral reefs record seasonal temperature changes, as can be used to explain variations in salinity. Low growth rates were closely associated with colder temperatures and greater cloud cover.




The stable oxygen isotope technique employed by Dunbar and Wellington (1981) has been used extensively to reconstruct past climates. Evans et al (2002) reconstructed Pacific sea surface temperatures from 1607-1990 by assessing stable oxygen isotope (δ¹⁸O) in coral. Sea surface temperatures were derived from oxygen isotope time series taken from 12 tropical Pacific Ocean, Indian Ocean and Red Sea sites. By comparing this data with similar attempts and historical data, it was possible to reconstruct sea surface temperatures in the Nino 3.4 region of the Pacific, the region where sea surface temperatures have the most significant impact on shifting rainfall patterns. Figure 1 presents the results of their reconstruction, indicating the number of El Nino Southern Oscillation (ENSO) warm events, where a sea surface temperature anomaly greater than 0.5°C was inferred from their investigation of coral reefs. 




Figure 1: Coral reconstruction of the number of ENSO warm events in NINO 3.4, 1607-1990 (Evans et al, 2002).

A similar technique was employed in a study by Urban et al (2000), in order to reconstruct ENSO variability over the past 155 years.  Negative oxygen isotope anomalies can be found in central western Pacific corals when El Nino events have increased sea surface temperatures and enhanced rainfall. In contrast, La Nina events (characterised by cool and dry conditions in this region) produce positive oxygen isotope anomalies. Coral from the Maiana Atoll was sampled and the bimonthly oxygen isotope record was used to infer climatic conditions. Figure 2 presents results from this paper, showing the strong correlation between oxygen isotope records in the coral and the instrumental sea surface temperature record. This indicates the potential of this method to reconstruct past climate.




Figure 2: Tropical Pacific variability from coral and instrumental data, 1950-1995 (Urban et al, 2000).

 

A review of present knowledge of tropical palaeoclimates derived from coral reef investigation was compiled by Gagan et al (2000). This article reinforces the benefits that the growing network of coral oxygen isotope records has for paleoclimatology. Constructing climate records that go back to the last deglaciation reveals previously unknown climate variability, such as ENSO cycles that exist on times scales of decades to centuries. However, there are still uncertainties involved with this method that stem from a lack of knowledge regarding the processes that control isotope changes within corals, and the specific climate mechanisms that produce these changes. A multi-proxy approach, combining records from ice cores, tree rings and sediment records is encouraged to ensure high-resolution paleoclimatology.

In the news this week . . .

Last week saw the 2011 instalment of the ‘Greenhouse Conference’ series, held in Cairns, Australia. Organised by Australia’s national science agency, CSIRO, the climate change focused conference covered a wide range of topics, including coral reefs. Speakers included Bronte Tilbrook, Ove Hoegh-Guldberg and Janice Lough who presented their findings from recent research projects. Tilbrook was speaking about the impact of ocean acidification on the Great Barrier Reef, with his research finding that the level of calcium carbonate was below the optimum level for coral reef growth. Although coral reefs appear to be growing, it is suggested that conditions in the Great Barrier Reef are not far from reaching a critical point, the full story was reported in the New Scientist. Hoegh-Guldberg told the conference that the future of the Great Barrier Reef would be determined in the next ten years, by then they will have reached a tipping point if anthropogenic degradation continues. A report on his comments can be viewed here. Janice Lough  spoke about the use of coral reefs to reconstruct past climate change. You can listen to an interview with her on Pacific Beat, courtesy of Radio Australia, talking about her research and the benefits of it. 




The benefits of assessing past coral reef response to climate change has been reinforced by a study led by James Klaus from the University of Miami. The study aims to determine the structure and function of these ecosystems during the Pliocene epoch, in order to assess how present day climate change will affect coral reefs. The findings suggest that modern day coral reefs are very different from Pliocene coral communities, as they were predominantly free living corals that were not attached to the sea floor. These species were adapted to higher sea temperatures and nutrient rich water, indicating the possible coral reef community of the future. The article was published in April’s edition of Geology. 




A ‘stress test’ has been developed by researchers from the Wildlife Conservation Society. The model aims to identify the coral reefs ecosystems that are most likely to adapt to climate change. It is hoped that by prioritising these regions then conservation and management projects will be more effective.




A project run by the Living Oceans Foundation aims to map shallow reef ecosystems around the world in order to develop an effective tool for managers. Over the next five years the team will identify shallow marine habitats, characterise the organisms that live there and develop an understanding of the key processes and interactions. It is hoped that the maps developed will aid effective management, and assist with modelling exercises. The full story can be viewed here.

Historic Sea Level Rise

As mentioned in the previous post, the potential response of coral reefs to present day climate change can be estimated through the assessment of the elevation and ages of drowned reefs. These drowned reefs also allow the investigation of historic sea level rise, which will not only improve our understanding of the changes brought about by a changing climate but will also enable more accurate predictions to be made about contemporary sea level rise. The last glacial to inter-glacial transition, which occurred around 13,000 – 10,000¹⁴C years BP, is the most studied due to the rapid climate change that occurred and the fact that it is the most recent transition (Hoek, 2008).




Figure 1: Caribbean sea-level rise during the last de-glaciation, with the shaded areas showing drowned reefs and the white areas indicating catastrophic rise events (CRE) (Source: Blanchon and Shaw, 1995). 

Blanchon and Shaw (1995) use drowned coral reefs in the Caribbean-Atlantic region to study ‘glacio-eustatic sea-level changes’ during the last de-glaciation. They emphasise the benefits of using coral reefs for studying sea level changes, referring to their suitability for radiometric dating and the way in which they maintain themselves at sea level through vertical accretion. In particular they investigate Acropora palmata, since it forms monospecific reefs and is strongly depth restricted, meaning it can be successfully and reliably used to infer the sea level. When sea levels rise faster than this species can grow vertically the reef will exhibit a mixed framework with other corals, eventually this is replaced by deep water corals. An inverse relationship has been uncovered between the rate of sea level rise and the thickness of this mixed framework layer. Figure 1 presents the sea level rise that occurred during the last de-glaciation, reconstructed from drowned reefs. The results indicate the large volumes of meltwater that entered oceans at three main points in time, and that sea level rise occurred rapidly. However, it also suggests that reefs were able to form again following the rapid sea level rise, which is good news considering the threats currently facing these ecosystems.




A similar study was carried out in Hawaii by Webster et al (2004) which attempted to investigate the reason for the drowning of the 150m submerged reef off Hawaii. Through radiometric dating techniques they were able to place the drowning of this reef at around 14,700 years ago which coincides with a sea level rise period known as 'Meltwater Pulse 1a'. The study not only provides evidence for the occurrence and timing of this meltwater phase, but also the intensity of the sea level rise (approximately 35m in 500 years, equivalent to 40-50mm per year). 

 


Figure 2: Position of drowned reefs in Hawaii. Reef 1 was subject to reef drowning following Meltwater Phase 1a (Source: Webster et al, 2004).

While the main process under investigation in studies like these is eustatic sea level rise, an understanding of  isostatic changes is required to infer eustatic sea level rise from the assessment of coral reefs. Stirling et al (1998) highlight the inconsistencies in the inferred timing and duration of the last interglacial as a result of isostatic processes that vary spatially.




From these studies it is evident that historic sea level rise caused by de-glaciation following the last glacial maximum caused the drowning of many coral reefs. However, it is also apparent that coral reefs were able to recolonize shallow regions of the ocean once sea levels were stable, which has positive implications for the consequences of present day anthropogenic changes.

Present Day Sea Level Rise

The IPCC’s Fourth Assessment Report (2007) predicts that global mean sea level will have risen between 0.18 – 0.59m by 2090, relative to 1980 levels (although there has been much debate over the accuracy of these predictions). Sea level rise is in response to a warming climate, which is currently causing the melting of polar ice and glaciers and the thermal expansion of the oceans. Coral reef ecosystems are dependent upon being able to maintain a certain level within the water, in order to receive sufficient solar energy. Global sea level rise is likely to affect coral reefs by reducing the amount of available sunlight and causing 'drowned' reefs. This happens when the sea level rises at a faster rate than coral growth, meaning there is insufficient levels of sunlight for the maintenance of zooxanthellae within the coral (Hoegh-Guldberg, 1999). Coral reefs are able to adapt to gradually rising sea levels by growing vertically. However, it is predicted that present day sea level rise coupled with ocean acidification (which reduces the calcification rate), will limit the ability of coral reefs to adapt.

An early paper that attempted to assess the threat of sea level rise to coral reef ecosystems published in 1988 by Buddemeier and Smith. This paper estimated that sea levels will rise at an average rate of 15mm per year, which is five times the modal rate of vertical coral reef growth. The authors expect the vertical growth rates to increase in response to rapidly rising sea levels, however they still conclude that this accelerated rate will be insufficient. The paper attempts to predict the response of coral reefs to sea level rise by assessing the maximum growth capacity of coral organisms. This is approached through the analysis of coral reef response during the period of rapid post-glacial sea level rise at the start of the Holocene and the last interglacial period. Their study suggests that rapidly growing corals will be more abundant, as this will enable the reefs to adapt. However, the success of coral reef adaptation is dependent on the level of sea level rise; if it exceeds the maximum growth rate of corals then many reefs will be lost. It is interesting to note that this article does not mention ocean acidification, which is now recognised as a limiting factor for coral reef growth. 




Done (1999) suggests that coral reefs will easily be able to adapt to sea level rise as they are capable of vertical growth rates of up to 20cm per year (compared with current sea level rise which is given as less than 1cm per year). However, he admits that the response will vary between and within regions, reflecting differences in species and the events and processes that operate at that scale.




Figure 1: Photos taken 6 hours apart on the Pacific island of Tuvalu, indicating the potential impact of sea level rise on low lying islands (Source: Gary Braasch).




Aside from the impact on coral reefs, sea level rise will also detrimentally affect coastal populations, especially those in low lying tropical regions where coral reefs are common. One of the most well publicised cases is the island of Tuvalu, which has been featured in the press and academic papers (Lewis, 1989; Church et al, 2006). Tuvalu is a low lying coral attol, where the highest point is less than 5m above sea level and is therefore likely to be one of the first casualties of a rising sea level. Vafeidis et al (2008) developed a global coastal database to assess sea level rise, within the DINAS-COAST project. It aims to support impact and vulnerability analysis to sea-level rise at a range of scales, by collecting high resolution data and will therefore facilitate future modelling exercises. It is this form of monitoring and modelling projects that will enable the better understanding of sea level rise, and the potential impact this will have on coral reef ecosystems and coastal regions.

In the news this week . . .

An article published in the Scotsman this week highlights the importance of Scotland's cold water coral resource. As outlined in the previous post, these deep water corals are highly vulnerable to disturbances and environmental change. A research team from Heriot-Watt University, Edinburgh is investigating the impact of ocean acidification on these ecosystems over the next few years through laboratory experiments and expeditions to the reefs.

The economic impacts of coral reef degradation was outlined in a Guardian article this week. It refers to the double blow currently being dealt to coral reefs from anthropogenic climate change and direct human impacts, such as damaging fishing activities, tourism and pollution.
 


The environmentalists favourite oil company Shell has been heavily crticised this week for planning an oil and gas drilling site thirty miles from the Ningaloo reef. Apparently the burning of fossil fuels isn't destroying coral reefs quick enough, so instead they have decided to take on a more direct approach. 

Ocean Acidification

Rising carbon dioxide emissions from human activities poses another threat to coral reefs in the form of ocean acidification. More than 30% of anthropogenic carbon dioxide emitted to the atmosphere is taken up by the ocean, a process which lowers the pH Sabine et al (2004). Increased ocean acidity affects coral reefs by reducing the calcification rate of reef builders and making coral susceptible to dissolution. The ability of coral reefs to produce calcium carbonate defines these ecosystems, and ensuring that a net surplus is produced enables reefs to build up. This documentary by the Natural Resource Defence Council provides a good deal of information regarding ocean acidification, and the potential impact to coral reef ecosystems:







Inorganic carbon, which is dissolved in the oceans, is used by coral organisms to deposit calcium carbonate. Increasing uptake of atmospheric carbon dioxide by the oceans requires carbonate ions that would otherwise be used by marine organisms to build shells or skeletons, as in the case of coral reef ecosystems. Decreasing carbonate ion concentrations is therefore likely to cause weak and brittle coral skeletons and slow growth rates. The chemistry of this process is relatively well understood, but the impact it will have on the global coral resource is heavily debated. Gattuso et al (1999) reviewed the carbon and carbonate cycle in coral reefs and the potential effects of human induced environmental change. 

  

Crustose coralline algae are an important calcifying organism in most marine habitats. In coral reefs they produce carbonate sediments and form coral reef structures out of carbonate fragments. Kuffner et al (2007) set up an eight week mesocosm experiment to quantify changes to calcifying components as a result of decreasing calcium carbonate saturation, which occurs with increasing carbon dioxide uptake by the oceans. They showed that the recruitment rate and growth of crustose coralline algae was significantly inhibited in mesocosms that had higher carbon dioxide levels. This study shows that ocean acidification has the potential to cause severe changes to benthic community structure in coral reefs, which will threaten coral reef ecosystems. 

 

This problem is not just restricted to tropical coral reefs, cold-water and deep water corals are severely threatened by ocean acidification. Their slow growth rate and limited ability to recover from disturbances make them more vulnerable to the effects of human activities. Turley et al (2007)  review the potential impact of ocean acidification on cold water corals, highlighting the lack of knowledge regarding these inaccessible ecosystems. They refer to a study by Guinotte et al (2006)  which predicts that 70% of known cold water coral ecosystems will be in water that has very low carbonate ion saturation levels, meaning it is unlikely that the corals will be capable of calcifying.
 


The ability of coral reefs to form calcium carbonate rapidly ensures that they are able to migrate upwards in order to adapt to changing sea levels. The threat posed to coral reef ecosystems by ocean acidification will limit their ability to adapt and could result in significant global losses of coral reef ecosystems. However, the impact of ocean acidification is not restricted to the reef building organisms. Many coral reef species produce calcium carbonate shells or skeletons that are central to their survival. Although there has been little research carried out on these species, Klepyas and Yates (2009) summarise knowledge regarding the effects of ocean acidification on these taxa in a special feature in the journal Oceanography. Deep sea sediment cores have provided a lot of information regarding past ocean acidification events, and have enabled an understanding of how these important coral species may be affected. Kump et al (2009) compares previous ocean acidification events to the human induced changes that are occurring today. Once again it appears the environmental changes that are taking place in our oceans are occurring at an unprecedented rate, a fact which questions the ability of coral reef ecosystems to adapt and survive.  

In the news this week . . .

Following on from the last post about the threats posed to Coral Reefs by rising sea surface temperatures, there is some good news from researchers at Southern Cross University's National Marine Science Centre. A team has been investigating coral bleaching at Lord Howe Island, which is located 500km off the coast of New South Wales. Warmer than average sea surface temperatures in 2010 caused mild to severe bleaching events in large areas of the coral reef, but according to Doctor Steve Dalton most sites are now showing signs of recovery. The full story can be viewed here.
 
A research team led by Dr Johnathan Kool of the Australian Research Council Centre of Excellence for Coral Reef Studies at James Cook University, has published a paper which reinforces the importance coral reef ecosystems have in maintaining marine biodiversity. The paper, 'Connectivity and the development of population genetic structure in Indo-West Pacific coral reef communities', presents results that suggest the Coral Triangle, which is the richest marine area in the world (located between Indonesia, Malaysia and the Philippines), is highly dependent on coral and fish larvae swept in from the South China Sea and Solomon Islands. Strong connections between these regions are responsible for the high diversity and resilience in the Asia-Pacific region. Dr Kool can be heard talking about his research in this region on ABC radio. The original news article can be viewed here.

Coral Bleaching

Coral bleaching refers to the whitening of coral following the loss or reduction in the symbiotic single celled organism zooxanthellae, which provide nutrients to the polyp through photosynthesis. This was first described by Peter Glynn (1984) following the 1982-3 El Nino event that caused mass coral bleaching in the Panama and Galapagos regions of the Pacific. Before the 1980s, most coral mortality events were localised and largely linked to factors such as storms and exposure to air during low tides. However, since the ‘80s there has been a marked increase in coral mortality events that are spread over large areas and due to coral bleaching, as a response to increasing sea surface temperatures (Glynn, 1992). Although the monitoring of coral reefs has been more extensive in recent years, anomalously high sea surface temperatures (linked to anthropogenic climate change) have been more frequent and caused widespread coral mortality.

Figure 1. Bleached coral at Reunion Island in the western Indian Ocean. (Source: John Pascal/ Agence pour la Recherche et la Valorisation Marines).

The global rise in sea surface temperatures that has occurred and which is predicted to continue as a response to increasing atmospheric concentrations of greenhouse gases, is likely to result in widespread coral mortalities, due to the sensitivity of coral to periods of thermal stress. One of the best sources of information regarding coral bleaching is the book ‘Coral Bleaching: Patterns, Processes, Causes and Consequence’ (van Oppen and Lough, 2008). The book looks at all aspects of coral bleaching, as the title indicates, at a number of scales and includes attempts to predict future scenarios. In this book a comparison is made between coral bleaching events in the Caribbean and Indo-Pacific, with those in the Caribbean being much more significant. The Caribbean coral reefs are much more vulnerable ecosystems, since they contain less biodiversity than those in the Indo-Pacific and have been more negatively affected during past climate changes (Smith and Buddemeier, 1992).

Severe bleaching events occurred in the Caribbean in 1995, 1998 and 2005, but they all had different impacts to the ecology of the reefs affected. ‘Caribbean Coral Reefs after Bleaching and Hurricanes’ (Wilkinson and Souter, 2008) reviews that status of reefs in this region following the 2005 event, predicts future changes and assesses the susceptibility of reefs. The 1995 event resulted in minimal mortality, even though widespread regions of coral reef suffered from bleaching. 1998 was the most detrimental event, with a reduction in coral reef cover of 50% in Belize. While the 2005 event affected the most widespread area, minimal mortality was reported compared to the two previous significant events. This has been attributed to the number of storms during this period, which mixed the waters and prevented ‘doldrum conditions’ that were linked with previous events. Looking to the future, this book suggests that the climatic conditions that lead to coral bleaching events are projected to occur more regularly over the next 20-30 years. Whether or not bleaching events will occur depends on the adaptive ability of corals and their symbionts. Current scenarios indicate that more than 75% Caribbean reefs will have to increase their thermal tolerance by 1-1.5°C over the next half century to avoid bleaching events occurring more than once every five years. Many biologists believe this time frame is too short to prevent widespread loss of corals.

While many of these papers present a fairly depressing picture of the future for coral reefs, there is some evidence that they have the ability to adapt to changing sea surface temperatures. Baker et al (2004) present findings from a study investigating the thermal tolerance of coral reefs across the tropics. Their results suggest that corals containing thermally tolerant symbiotic algal species are more abundant on reefs after severe bleaching events. Adaptive shifts to these species will improve the resistance of affected coral reefs to future bleaching events, and therefore has the potential to prevent mass extinctions. However, the speed of change may well prevent these adaptations from occurring.

In the news this week . . .

A report published this week by the World Resources Initiative has caught the attention of news agencies around the world. Reefs at Risk Revisited (Burke et al, 2011) updates a 1998 report which assessed the main threats to the global coral reef resource. This time the study includes climate related threats, which contribute to the mounting pressures on coral reefs. The report estimates that 75% of coral reefs are currently at high to critical threat levels, a figure that could exceed 90% by 2030.  The Reefs at Risk research initiative aims to advance understanding regarding the spatial distribution of threats to coral reefs worldwide, providing essential information for the development of conservation strategies. 




The Encyclopaedia of Modern Coral Reefs; Structure, Form and Process will be launched today at the James Cook University in Townsville, Australia. The encyclopaedia is an extensive collection of knowledge regarding coral reefs and weighs four kilos! 




A research expedition investigating coral reefs in Semporna, Malaysia has claimed to have found the most biologically diverse coral reef in the world. 43 species of mushroom corals, which act as a proxy for species richness, were identified (the previous record was 40) as well as 844 species of fish. This study indicates the biological wealth of coral reefs and proves that some coral reef ecosystems are still in fantastic condition. Hopefully papers like this will inspire conservation initiatives and help to preserve this globally important marine resource.

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.

Climate Change and Coral Reefs: An Introduction

This blog will attempt to cover the main impacts of a changing climate on coral reefs, through a discussion of key academic papers and a look at issues that hit the headlines and social media. Whilst many would perceive climate change to be a contemporary issue, coral reefs have been affected by the impact of a changing climate throughout their history. Not only does this allow the investigation of past changes to sea surface temperatures and sea levels, but will enable the simulation of future changes.

My own experience of coral reefs is fairly classic of anyone who has been to Australia! In the time I was there I spent the odd day snorkelling off the coast of Queensland, exploring reefs by boat on organised trips and under my own steam at the many islands scattered across the Great Barrier Reef. Although I'm told the best reefs are far out to sea, and many are protected from the likes of people on their gap year, the areas I went to were fairly disappointing. Especially having seen other traveller's photos of the Ningaloo Reef in Western Australia, where the coral seemed to incorporate every colour of the rainbow, reef sharks and loggerheads were plentiful and shoals of fish were vast. It appeared evident that the dual blow being dealt to these fragile ecosystems by tourism and, more significantly, climate change was having a severe impact.

Ove Hoegh-Guldberg's (1999) paper is a good place to start, as it considers the primary impact of a warming climate on coral reefs - coral bleaching. Rising sea temperatures result in the required temperature for corals, and the photosynthetic single celled organisms (zooxanthellae) that have a symbiotic relationship with them, to be exceeded. This can cause mass coral bleaching events due to the zooxanthellae, that give the coral its colour, being expelled or dying. As well as allowing the development of coral bleaching knowledge, this paper also models future changes, unfortunately painting a fairly grim picture. It suggests that mass coral bleaching events will become much more commonplace and that current warming cannot continue without the global loss and degradation of coral reef. Although sea surface temperatures have increased in the past, the speed at which change is currently occurring prevents the marine ecosystem from adapting to change.
DOI: 10.1071/MF99078