Climate Change Implications on Great Barrier Coral Reefs - Term Paper Example

Climate change implications on Great Barrier Coral Reefs The recent global trend for climate change is now well established, with the average surface temperature on Earth rising by 0.6 plus or minus 0.2 degrees centigrade since 1900, and the temperatures appear to be escalating at levels which are much greater than what they have been in the past 1000 years (IPCC, 2000 in Hughes, 2003). The ensuing climactic changes have also produced changes in wind velocity and direction. Coral reefs are among the most spectacular marine ecosystems and the greatest diversity of species may be noted on the Great Barrier Reef in Australia. These are very productive ecosystems that are able to survive and are highly productive in waters that are low in the nutrients required for primary production; as a result they have a tremendous beneficial effect on other forms of marine life in the region. The benefits of coral have been listed by Carte (1996). At the outset they are excellent sources of income because of their tourist attraction, with thousands of tourists visiting the Great Barrier Reef for scuba diving. The coral reef ecosystems are also invaluable in providing a fertile environment within which fish are able to thrive; as a result, fisheries are associated with coral reef systems and generate a considerable amount of wealth for Australia. Since there is such an abundance of fish thriving in the coral reefs, they also provide a source of protein for poorer countries through a diversion of supplies to those countries (Bryant et al, 1998). Thirdly, coral reefs are also effective in protecting coastlines from erosion, flooding and damages caused due to storms, because they function as a barrier to wave action. The upheavals in climate may however, be causing some damage to the Great Barrier reef and eroding its properties; the same properties that have contributed to all the advantages it has. This report examines the impact of these climactic changes upon the various species of coral found on the Great Barrier Reef in Australia. The impact of rising global temperatures: Rising temperatures have a detrimental impact upon coral because they cause bleaching; when the thermal tolerance level of the corals are exceeded, then there is a corresponding explosion in their composition of photosynthetic symbionts or zooxanthellae, which in turn leads to bleaching (Hoegh-Guldberg, 1999). When the corals are bleached white, it means that their zooxanthellae are destroyed, thereby damaging this life form. Bleaching is associated with coral mortality, with the intensity of temperatures, corals such as pocillopora, staghorn corals or Acroporidae, Acropora hyacinthus and Acropora gemmifera have disappeared, and Hoegh-Guldberg (1999) estimate that several species of coral which are 700 years old have died out due to bleaching, although corals are capable of surviving almost up to 1000 years. In general, corals are able to respond to natural variations in climate through the processes of acclimatization or modifying the cellular metabolic processes in such a manner that they are able to function at different temperatures. Alternatively, corals may adapt, such that only the species that are able to survive in higher or lower temperatures as the case may be, would tend to survive while the less resistant species would die out. Such acclimatization or adaptation however, is a slow process which takes decades to accomplish and corals are finding it difficult to survive in the rapid pace at which global temperatures are rising. Corals and their zooxanthellae have different thermal optima and maxima, hence they have adapted differently depending upon the region they are found (Hoegh-Guldberg, 1999) and according to Salih et al (1999), the intertidal corals which have fluorescent pigmentation are more likely to be able to tolerate heat stress as opposed to those corals without fluorescent pigmentation. Yet another detrimental impact of persistent or rapidly changing high temperatures is the inhibition of the reproductive capacity of corals, as a result of which the coral population begins to decline. This is especially the case in flat reef corals, which when bleached appear to stop producing eggs altogether. Some of the species of coral which have been affected in this manner include the Symphillia species, Montipora, Favia,Goniastrea, and Platyguya daedalea. The acropora species is also susceptible to reduced reproductive capacity due to intense temperatures; some of the species which are slowing down in terms of their reproductive rate include flat reef species such as Acropora aspera, Acropora palifera, Acropora. pulchra and M. Digitata. Since the development of gonads is slowed down due to bleaching, intensity in temperatures does not work to the benefit of corals. When there is a slow down in the reproductive rate, this also means that the coastline is not able to recover as quickly from erosion of the coastline. The argument that the acropora species is responding negatively to rising temperatures has however, not been corroborated in other studies, which suggest that the most vulnerable species, i.e., Acropora, pocillopora and porites are actually developing thermal resistance.(Maynard et al, 2008). In this study, the authors have pointed out that after the extensive bleaching of corals along the Great Barrier Reef in Australia in 1998, a subsequent event which occurred in 2003 causing even more thermal stress, did not result in further losses of the acropora species. Rather the authors point out that the bleaching severity in 2003 was actually 30-100% lower than what was predicted on the basis of the relationship between thermal stress and the severity of coral bleaching in 1998. This was the case despite the higher incidence of solar irradiance and mortality rates being lower does tend to suggest that the species which were thought to be vulnerable, i.e, acropora, pocillopora and porites had all acclimatized to some degree so that they were better able to cope with the thermal pressures when there was a recurrence of the stresses that occurred earlier. According to Goreau and Macfarlane (1990), one of the most important functions of corals is to sustain the reef and the coastline through their fast growth and repair capabilities which also encourages fish to thrive. When subjected to bleaching however, corals not only reduce their rate of growth, they also become calcified after losing their zooxanthellae, which reduces the available energy which can be used by the ecosystem. This also affects other forms of life. It must however, be noted that not all corals appear to be susceptible to the thermal stresses and despite the rapid rise in temperatures, appear to remain largely unaffected, for example species such as Coeloseris mayeri and Symphillia radians, which were not even bleached in the high temperatures and appear to be thriving.(Fisk and Done, 1985). The impact of changing wind velocities and directions: Wind data over the Heron islands, which is located inside the Southern Great Barrier Reef from the years 1962 to 1980 have shown that the annual wind energy vector has oscillated from its original position in the early 1960’s, i.e., SSE to an ESE direction in the 1970s (Flood, 1986). With such a change in the wind velocity and direction, there is a corresponding impact upon the direction in which waves are propagated and consequently, the manner in which the coral sand cays in the region are being shaped. Flood (1986) argues that the changing shoreline of Heron islands that is caused by soil erosion may not necessarily be caused by tourist overcrowding or abuse; rather it may be a symptom of climactic changes which are changing wind directions and velocity and thereby altering the formation of the coral cays. It also appears that depth may have an impact upon the extent to which climactic changes may produce bleaching and therefore destroy coral. Fisk and Done (1985) found that the windward side appears conducive to bleaching while corals on the leeward side are less susceptible. They noted bleaching among the corals in the Great Barrier Reef up to a depth of 15m, but below the 10m mark, fewer corals were damaged, for example only the Seriatopora hystrix and Montipora foveolata were affected by the winds and rising temperatures. Changes in climate also affect corals when sea levels rise or when the alkalinity of the water changes. The greenhouse effect has produced a higher concentration of carbon dioxide in the atmosphere and carbon dioxide above the water produces changes in the concentration of chemical species like protons and carbonate ions, as a result of which the acidity of the water increases. The sea water exists in an aragonite saturation state which is likely to decrease with an increase in the carbon dioxide concentration of the water.(Gattuso et al, 1998). As opposed to the calcification caused by rising water temperatures, the changing aragonite balances in the water is expected to decrease the calcification rate of corals by 14 to 30% by the year 2050. The extent to which acclimatization might take place cannot however, be accurately predicted. Conclusions: In conclusion, it may be noted that the evidence which exists suggests that while there is a definite negative impact on some species of corals due to climactic changes, there is some acclimatization which appears to be taking place. The rapid pace of rising temperatures may be detrimental to corals because they cause bleaching. Several species of the Acropora corals have died out due to the intense high temperatures which have caused bleaching and killed off their zooxanthellae and it has been estimated that between 20 to 100% of corals have perished. As also detailed earlier, the high temperatures are also causing the slow decline in several species of corals, notably the acropora species, by slowing down the production of gonads and thereby reducing the reproductive capacity of these corals, which in the long run would also cause a dying out of the species just as they are dying out because they are unable to bear the intense heat. This is especially damaging because the acropora species has traditionally been one of the fastest growing species of coral. Since corals cannot adapt quickly, it appears likely that intertidal corals with fluorescent may be most likely to survive provided sea temperatures stabilize. However, based upon the observations of experts as detailed earlier, some of the vulnerable coral species may also be acclimatizing themselves to the higher temperatures and may therefore be able to adapt themselves and survive in a new and different environment generated by the climactic changes. The literature review above also suggests that climactic changes as evidence din rapidly rising temperatures and changing wind velocities and directions may not always have a detrimental impact upon all corals, in fact some coral species appear to be quite resilient and remain unaffected by the climactic upheavals. Similarly, the literature review also suggests that the calcification of corals may not take place as rapidly as projected because yet again, some acclimatization may be taking place to reduce the calcification rates. Hence, on an overall basis, no definitive projections can be made; however it does appear that some existing species of corals like acripora may not be able to survive and may become extinct as they die out. The coastline of the Great Barrier Reef is changing and is not as self regenerating as it was before because the pace of such regeneration may have slowed down considerably. While the shape of the Great Barrier Reef is changing however, corals may still survive, especially species such as fluorescent intertidal corals or those corals which are able to become heat resistant. It also appears likely that many species of coral may adapt and acclimatize their metabolic activity in such a manner as to ensure their survival. References: Bryant, Bryant, D., Burke, L., McManus, J., and Spalding, M, 1998. “Reefs at risk: a map-based indicator of threats to the world’s coral reefs”, World Resources Institute: Washington, DC. CITED in: Guldberg, 1999. Carte, B.K., 1996. “Biomedical potential of marine natural products”, BioScience, 46:271-86 IPCC, 2000. “Climate change 2001: the scientific basis”, CITED in Hughes (2003) below. Flood, P.G., 1986. “Sensitivity of coral cays to climactic variations, southern Great Barrier Reef, Australia, Coral reefs, 5:13-18 Gattuso, J.-P., Allemande, D., and Frankignoulle, M, 1999. “Photosynthesis and calcification at cellular, organismal and community levels in coral reefs. A review of interactions and control by carbonate chemistry”, American Zoologist, 39, 160.83. Goreau, T. J., and MacFarlane, A. H., 1990. “Reduced growth rate of Montastrea annularis following the 1987.1988 coral-bleaching event”, Coral Reefs 8: 211.15. Hoegh-Guldberg, Ove, 1999. “Climate change, coral bleaching and the future of the world’s coral reefs”, Marine Freshwater Research, 50: 839-66. Hughes, Leslie, 2003. “Climate change and Australia: Trends, projections and impacts”, Austral Ecology, 28: 423-443 Maynard, J.A., Anthony, K.,R.N., Marshall, P.A. and Masiri, I, 2008. “Major bleaching events can lead to increased thermal tolerance in corals”, Marine Biologist, 155: 173-182. Salih, A., Cox, G., and Hoegh-Guldberg, O, 1997. “Photoprotection of symbiotic dinoflagellates by fluorescent pigments in reef corals. In.Proceedings, Australian Coral Reef Society, Heron Island 50 year commemorative meeting.. (Eds. J. G. Greenwood and N. Hall.) pp. 217.30, (University of Queensland Press.) Read More