Impact of El Niño Southern Oscillation on Coral Reefs

Impact of El Niño Southern Oscillation on Coral Reefs

It has been well documented that rising temperatures are causing mass bleaching of coral reefs and putting the population of coral reefs under threat. This is partly due to anthropogenic warming, but there is a natural phenomenon that is causing temperatures to rise. This is known as El Niño. The idea of this is that trade winds at the equator cause ocean currents in the East Pacific to upwell from deep in the ocean. This helps to keep the average temperature of the East Pacific relatively cool. The current then proceeds west. As it moves in this direction, it is heated by the sun, meaning temperatures in the West Pacific are up to 10 degrees warmer than in the east. When an El Niño event occurs, this current that cools the East Pacific will significantly weaken, or may even disappear completely. This results in the East Pacific being pretty much the same temperature as the West Pacific.

This higher ocean temperature in the East Pacific is not good news for corals.  The ENSO has been identified as the trigger of bleaching in the Eastern Pacific. Studies in the Java Sea have shown just how big an effect El Niño can have on coral reefs. The 1982/83 warming event meant that average sea temperature was raised by 2-3 degrees over a six month period. This rapid warming was too much for corals, with between 80-90% of corals having died at test sites. This is obviously a massive blow to coral population, as well as significant damage to other marine life that lives in and around the coral. As seen in Figure 1, the Java Sea borders Java, Sumatra and Borneo. These are all heavily reliant on tourism and the loss of 80-90% of the areas coral reefs would have been a significant deterrent to tourists. Five years after the study there was a recovery of sorts, however the coral population is still at around 50% of previous levels.

 

 Figure 1- Map of the Java Sea and surrounding area.

 

Gill et al. (2006) showed that high levels of aerosols (dust and sulphides, largely created by volcanic activity) effectively mitigated bleaching conditions, even during ENSO years that would normally have created bleaching-favourable conditions. An El Niño event coupled with a period of anthropogenic warming could prove catastrophic for coral reefs. Having said this however, there have been several El Niño events since the mass bleaching event in Indonesia without there being such a pronounced effect on the coral population. This means that there must be other factors affecting coral reefs, not just the ENSO. The variety of factors affecting coral reefs in the South Pacific means that quantifying the impact of these events on coral reefs is very difficult, however it is certain that they will be important to the future survival of coral reefs.

Sources

http://www.sciencedirect.com/science/article/pii/S0272771408003405

http://link.springer.com/article/10.1007/BF00265007

 

Solutions to the Problems of Coral Reefs

We have seen in the last blog that the World's Reefs face a challenge unprecedented in the past due to a variety of reasons, such as bleaching due to elevated global temperatures, overfishing and pollution, blast fishing and coral mining to name but a few. Humans have had the biggest impact on coral reefs. This can be seen by looking at he geological record, where there is a clear analogue which can be measured against present day levels. Coral reefs are likely to have never been under this big a threat. They face complete eradication, but how can this be prevented?

Well, there are many factors affecting coral reefs, so it is likely that several different courses of action working in tandem will be required. Hughes et al. suggested that 'strong policy decisions to reduce the rate of global warming' were required to protect coral reefs. This was back in 2003, and there has yet to be a clear set of decisions made in order to reduce the impact on coral reefs. There has been a distinct lack in clear global action.



Despite the lack in concerted global action, there have been several localised attempts to preserve coral reefs. For example in the Maldives, where coral reefs have massive economic value, there have been numerous restoration projects including clipping and replanting of coral, in order to keep the population at acceptable levels.

Maldives Reef that has experienced bleaching.

Banning the dumping of waste from farms, industry and households into the oceans and rivers and beach clean ups are both examples of simple methods that could be employed to ensure the future of coral reefs. Sustainable fishing is slightly harder to implement, however it would have a big impact on the coral. Healthy fish populations and healthy coral reefs go hand in hand. Not enough fish will result in algal blooms near the surface of the ocean. This will mean less sunlight will reach the coral further down in the water column. As they feed through photosynthesis you can see why this is a problem.



The main issue faced by coral reefs is the rising sea temperatures. In order for this to be reduced, the amount of co2 coming from anthropogenic sources needs to be reduced. This will involve a complete change in attitude from humans. We can't keep thinking it is alright to pollute the earth with little regard for the consequences. We need to stop the problem at its source, not focus on clearing up the problems afterwards. Reduction of co2 and changing attitudes will take a long time to take place however, and will involve lots of political protocol to organise such changes. Like Hughes said back in 2003, the world powers need to come together to solve this problem. In the meantime, 'stop gap' solutions will be required to allow the coral to recover and so that things do not get to the irreversible
stage.



Sources

1. Climate change, human impacts and the resilience of coral reefs, Hughes et al 2003
2. Phase shifts, herbivory and the resilience of coral reefs to climate change, Hughes et al 2007

World Resources Institute- Reefs Revisited

This second blog post will focus on the World Resources Institute Reefs Revisited report. This was published by the WRI in 2011, and was a follow up to the original report published in 1998. It was published to raise awareness of the threats posed to coral reefs and also outlined methods to help combat the threats that are faced by corals.

Reefs revisited is going back to the worlds coral reefs to see whether they are still in danger, and if they are, what can be done to combat this change.

The study found that there are 800 types of coral around the world, so diversity is still at good levels. However since the original report was published, there have been vast increases in population. This has led to an increase in industrialization, agricultural development, commerce and greenhouse gas emissions. This all has an effect on global temperature, which then affects coral reefs. The ocean temperatures and ocean acidity is now the highest they have been for 400,000 years. The higher temperatures will result in bleaching. Bleaching is when the higher temperatures forces the symbiotic algae to leave the coral reefs, and so they will be ‘bleached’ as the algae is the component of coral’s colour. The loss of this bacteria makes it very difficult for the coral to feed as they can no longer use photosynthesis. It will force the coral into an almost torpid state. It is possible for them to come out of this bleached state, however in order for this to happen ocean temperature must decrease.

FIGURE 1

From Figure 1, we can see that the corals have been classified depending on how threatened they are. Blue is low threat, yellow is medium, red is high and purple is very high. Large portions of the Great Barrier Reef is classed as low which is promising as this is the largest coral reef found in the world. Worryingly, large proportions of Indonesia and Thailand reefs are rated as high threat. this could be due to poorly governed tourism in the area.

The study identified threats to coral as being either global or local. Local threats are those that take place in close proximity to the coral, which includes more sewage discharge and watershed based pollution, as well as higher levels of reef erosion. Global threats are threats that effect the coral indirectly, through human impacts on global temperatures and ocean chemistry.

The combination of both local and global threats leaves coral reefs largely under threat. The study found that when thermal stresses are added to the local stresses of the different reefs, 75% will be classed as threatened. This is a troublingly large number. Looking at individual areas, we can see that the most at risk area is Southeast Asia, where 90% of reefs are classed as threatened. These provide a great source of income for countries such as Thailand and the Philippines. Tourism and fishing are massive factors for these economies, and so without the coral reefs there will be widespread unemployment, as many regions are dependent on the coastline and what can be found in the oceans. The story doesn’t get much better as you move to other areas. The Atlantic Ocean’s reefs are threatened at a rate of more than 75%, with over 30% as very high risk. The Pacific Ocean is the least at risk, but still with 50% of its reefs threatened. This is obviously a problem that is not going to get better by itself. Going back to the effect this will have on countries such as the Philippines, we can see the magnitude of the effect of lost coral reefs on coastal communities. 275 million people throughout the world live within 30km of coral reefs. The socio-economic factors associated with loss of coral reefs include:

• Changes in the fish population that surrounds the reefs. Bleaching could lead to fish moving away from the reefs, meaning fishermen then struggle to catch enough fish to make a living.
• There may also be a decrease in the species diversity when corals become bleached, and so the amount of tourism may decrease as the reefs are no longer as attractive as there are less fish. Tourism is a large part of the economy for many of these reef-bearing countries such as Thailand, and a loss in tourism would substantially lower GDP (looking at the Maldives, 96.5% of their GDP is dependent on tourism, so they absolutely cannot afford to lose their coral reefs).
• The reefs also provide a large reserve of pharmaceutical materials, which if bleaching persists will mean a lack of medicine for people locally and globally. Many people in poorer countries will not be able to afford increased prices in medicinal care.

 

So as we have seen then, the report doesn’t look too promising. With so much of the world’s reefs threatened, is there any way of salvaging them? Well there may be, if action is taken promptly, and the action is widespread. The report outlined ways in which coral reefs can be saved. Reducing the amount of co2 emitted into the atmosphere is one way of ensuring the survival of coral reefs. Less co2 will help to reduce temperatures as the greenhouse effect caused by co2 and other particulates will be reduced. There are other methods suggested as well, such as managing coastal development, preventing local threats such as pollution into the ocean from taking place. Action needs to be taken soon, as coral reefs don’t have long before it is too late.


the full report can be downloaded here: http://www.wri.org/publication/reefs-risk-revisited