Human Threats to Coral Reefs and Coral Damage (continued)

Sedimentation can also occur, which can have similar effects on corals to algae preventing sunlight from reaching the corals. There are a number of causes of sedimentation, such as soil erosion, dredging, deforestation and construction. Sediment as a by-product from activities such as these can suspend in the water and block light reaching zooxanthellae. Unfortunately, the majority of sediment is entering the oceans in developing countries with high coral reef densities (Birkeland, 1997), therefore the sedimentation is having much more of an effect on the ecosystem than it would otherwise have in regions with less coral reefs. The countries producing the highest levels of sedimentation include those in South East Asia and in the Western Pacific. In fact, almost 100% of all the sediment entering the oceans originates from these areas (Birkeland, 1997). Sediment can also form a thin film on the upper surface of coral, which can be removed by direct movement of the polyps, via secretion of mucus from the mucus glands within the polyps, or tissue swelling (Weber et al., 2006). However, these solutions use up resources, and therefore if these defensive mechanisms are sustained due to settling sediment over long periods the polyps may become damaged, and can die in extreme cases. Damage to the coral, and its recovery, is directly related to the sediment type as well as the quantity (Weber et al., 2006). High nutrient sediment has been found to lead to greater stress levels in corals than lower nutrient sediment. In Puerto Rico, reefs subjected to high levels of sediment influx had significant loss of coral species in comparison to other locations. Most of the species affected usually reside in other geographical locations in deeper water, from 25-30m, but due largely to the lack of light caused by the sediment these coral species cannot survive, leading to reefs occurring only in shallower waters (Acevedo et al., 1989).

Human Threats to Coral Reefs and Coral Damage (Continued)

The twentieth century introduced another threat to coral reefs, in the form of weapons testing. However, opinions differ as to whether testing does in fact have a long term detrimental effect to reefs. After World War 2, between 1946 and 1958, testing of the nuclear bomb was carried out in the atolls of the Pacific Ocean by the US (Reuther, 1997). Atolls are circular coral islands that enclose a central lagoon, often occurring on top of submerged mountains or volcanoes. The most notable nuclear testing was carried out on the Marshall Islands, or the ‘Pacific Proving Grounds’. It is thought 67 bombs were tested in this period, and clearly had direct effects on the surrounding reefs. One bomb, codenamed Castle Bravo, was detonated in 1954 at the Bikini Atoll, the first testing of the more powerful hydrogen bomb. Its yield was underestimated by the military by two and a half times and as a result had significantly high impacts on the environment, spreading nuclear fallout over thousands of kilometres, infringing on many other reefs and inhabitants (Reuther, 1997). Some data, however, shows that the ecosystem in these areas is in pristine condition, and that species that were affected at the time have quickly recovered. For example, in France, despite direct damage to coral caused by explosions, there is little evidence to suggest the balance of species has been affected long term. Data shows that loss of fish species was complete in the area most affected by the bomb. However, recovery of the populations, initially via immigration followed by reproduction, was very swift, lasting just 1-5 years (Planes et al., 2005). In this case the coral habitats for species were not badly damaged, so it seems as though as long as the habitats are not badly damaged, and niches remain free, coral communities may recover fairly quickly in the case of nuclear weapons. Another study on coral reef gastropods in French Polynesia gave similar results. Populations of gastropod fell immediately after nuclear testing, but they were quickly able to recolonise empty niches left as a result of the bombs (Lanctot et al., 1997).

Human Threats to Coral Reefs & Coral Damage (Continued)

In areas where standard military weapons testing takes place, studies on the reefs have shown them to be in pristine condition. This could be because as the military occupy these regions, detrimental human activities such as fishing, sedimentation and pollution cannot take place without civilian human presence and so, despite minor habitat damage from explosions, coral organisms can thrive (Spalding et al., 2005). Differing results from studies on weapons testing have lead to no definite conclusion as to the impact such actions have had, and are having, on coral reefs. Further investigations need to be carried out in order to increase our knowledge on the effects of weapons testing on coral reefs.

Summary and conclusion

It seems clear from numerous investigations that human influences are severely harming the health of coral reefs (Reaser et al., 2000; Obura, 2005; Barber et al., 2001). Fishing and sedimentation in particular appear to be having a large impact, with nutrient enrichment seemingly slightly less damaging. More studies into the effects of weapons testing need to be carried out in order to determine their impact, although the discontinuation of nuclear testing in the Pacific atolls could make the results of these studies of less value. However, climate change appears to offer the greatest threat to coral health. Steadily rising SSTs over time have led to stronger ENSO events, and in turn mass bleaching events have increased. Bleaching events brought about by the climate are much more widespread and directly affect far more corals than any of the other human factors mentioned, which apply to more local areas of coral. Although the timescale being studied is a small one, it seems as though the rising temperatures are a result of climate change and not one-off events. Whether or not global warming as a result of increasing greenhouse gases in the atmosphere is occurring is unproven and open to speculation, but it seems likely in my opinion that there is a significant human aspect to this phenomenon.

Conclusion (Continued)

Further studies to improve our awareness of coral reef ecosystems could include selecting a coral native to a particular region, and exposing it to different species of zooxanthellae in turn. There is current evidence, as stated earlier, suggesting that after bleaching, corals become recolonised by more resistant zooxanthellae (Kinzie III et al., 2001; McClanahan, 2000). Running experiments on this topic will lead to a better understanding of recolonisation and this will lead to a better insight into the changing diversity and adaptation of zooxanthellae. This could aid in the long term conservation of coral reefs. Also further experiments to gauge the natural ability of corals to acclimatise to increasing temperatures may be useful.

Although susceptibility models already exist, such as that developed by Maina et al. (2007), it would be beneficial to continue designing models to predict the effects of non-steady state processes such as climate change will have on coral reefs in the future (Crabbe, 2007).

Conclusion (Continued)

I also agree with the views of Nystrom & Folke (2001), who suggest more trans-continental studies into reef resilience, as the majority of studies conducted in the past have focused on collections of reefs in a small geographical range. These further studies will hopefully aid in the conservation of coral reefs, as well as help gain a further insight into the ways climate change may affect the interactions between reefs.

Genetic studies could also be carried out on resistant species of corals and zooxanthellae in order to determine which genes they possess that give them a greater resilience to environmental extremes.

Conclusion (Continued)

There are extensive management issues that must be addressed in order to reduce coral reef damage. Education and communication are perhaps the most important, as at present many people are ignorant to the effects of, for example, pollution, climate change and overfishing. Educating communities will allow changes to be made locally to the management of crucial issues such as those explained earlier.

In a recent survey amongst 286 scientists (2007), reducing atmospheric carbon dioxide emissions was ranked as the second most effective change to be made to help improve the health of coral reefs. This is because it seems probable human behaviour resulting in CO2 emissions is at least partly responsible for the slowly increasing global temperatures and extreme environmental conditions that impact upon reefs via bleaching. This is a global problem however and requires participation from many countries in order to have a significant impact.

Conclusion (continued)

Stricter regulations on fishing should be introduced in certain parts of the world, as currently it is being carried out at an unsustainable level that is damaging to the reefs. If corals are to continue to thrive fishing must be carried out at a sustainable level via improved management. Studies based on an existing bio-economic model, the Gordon-Schaefer model, show that in many regions where fishing exceeds recruitment a reduction in fishing of approximately 60% is needed in order for fish stocks to return to a steady equilibrium. A complete ban on blast fishing would also be beneficial due to its direct destructive effects on the coral reefs and their organisms.

Finally, advances in waste management should be made, especially in China, which, due to its rapid industrialisation, is the main contributor to the pollution of coral reefs. However, in reality, due to the political situation in the country, and the speed of industrialisation, major reductions in pollution in the near future seem unlikely.

Introduction to Coral Reefs

Coral reefs that exist today are generally less than 10,000 years old. However, they have been around for over 500 million years, acting as a backbone for many coastal ecosystems. They play a significant role in food production supporting countless other organisms that rely on their health for their own survival. Not only are reefs important for biological reasons, they also have huge socio-economic impacts on nearby communities. However, evidence shows the health of coral reefs is currently in decline, with fears that human impacts are facilitating the destruction of these extremely diverse ecosystems. This research will look at what corals are and how they function; their role in ecosystem health and human society; and then focus on the human-influenced reasons why reefs are in decline, specifically looking at a process known as coral bleaching. This research will conclude with a look at the future prospects of corals and the sustainability of their health.