Zooxanthallae and Bleaching

In the past blog posts we have looked at changes to the corals in the Red Sea and the Barrier Reef, but now it is time to go down in scale, and take a look at something much smaller. Zooxanthallae, as mentioned in previous posts, are photosynthetic bacteria that allows corals to feed. We will take a closer look at the relationship between the two, and how changing environments is resulting in bleaching. 

An enlarged view of the microscopic Zooxanthallae.

The relationship between coral and zooxanthallae is mutually beneficial. The coral provides a safe environment for the zooxanthallae. The bacteria can then produce oxygen and glucose whilst removing waste (this is photosynthesis). This allows the coral to feed and can remain sessile. This is a very important relationship as otherwise the coral would struggle to feed itself, as they cannot photosynthesise themselves. From a more commercial viewpoint, the bacteria is important as it is the zooxanthallae itself that provides the colour for the coral. The bright vibrant colours attract various marine life such as fish, which in turn attracts tourists to destinations all over the world. Thus the relationship helps to bring in an estimated $9.6 Billion per year through coral reef generated tourism. As the bacteria requires sunlight, corals need to exist in shallow, clear oceans. However due to anthropogenic activity, the pristine environment which allows this relationship to flourish is being put under incredible strain.

Corals and zooxanthallae are being put under extreme pressure by rising temperatures. Higher temperatures will result in the bacteria being expelled from the coral. As they bacteria determines the colour of the coral, the coral will become white. This also means that the coral has no way to obtain food. They are not dead however. They can remain almost in a state of hibernation for some time. This gives the conditions a chance to return to acceptable levels. If this happens then the bacteria will return to the coral and the relationship will be back on track. However too long without being able to 

feed will result in the death of the coral. 

The threshold at which the bacteria will leave the coral depends on different types of coral and zooxanthallae. Exposure to high temperatures (32 degrees and above) for as little as 7 hours can result in expulsion of zooxanthallae at 1000 times the normal rate. This shows just how sensitive the corals and bacteria can be, especially to storm events, where there are isolated incidents of rapid 

heating. For example there was mass expulsion of zooxanthallae in Jamaica after Hurricane Flora. Having said this, the corals examined in the study returned to normal after 17 days, so there is some hope for corals, as they are resilient. 

Coral and zooxanthallae have evolved together so they are almost thought of as one. Bleaching remains a serious threat to the coral, and they could be completely destroyed as a result of it. So much would be lost if this were to come to fruition, and the worlds oceans may never be able to recover. 

Sources

1. https://themarketmogul.com/the-economic-impact-of-coral-reefs/

2.http://www.sciencedirect.com/science/article/pii/0022098189901093

Case Study- Red Sea Coral Reef

The Red Sea Coral Reef is the second largest in the world in terms of length, at 1900km long and has an area of 438,000km2. The only coral reef that is longer is the Great Barrier Reef. The Red Sea is located in between Africa and Asia, and is a seawater inlet of the Indian Ocean. Corals in the Red Sea are aged up to 5000 years old. The majority of the coral forms around the shoreline.

The Red Sea Coral Reef

The dominant coral genera are Porites and Acropra. These are both types of stony corals, covering hundreds of species.  Acropora in particular is well suited to reef building as it is very good at taking up calcium carbonate from the water. The coral reefs in the Red Sea are some of the most robust in the entire world. They have a high tolerance to temperature and salinity. The fact that it is resistant to higher temperatures is particularly important due to predicted increases in ocean temperatures. In 2011, the temperature of the Red Sea had increased by 0.7 degrees since 1994. With temperatures set to rise at a faster rate, the durability of these corals will be invaluable.

An example of Porite Coral

The largest portions of the coral reefs can be found in the northern area of the Red Sea, near Egypt and Saudi Arabia. There are smaller amounts of coral to the south of the Red Sea due to the influx of material from the Indian Ocean. There is also a larger amount of mixing due to higher wind speeds, which will mean that coral reefs struggle to develop. This is because more sediment prevents the production of calcium carbonate, which is needed to secure the base for coral reefs.

 As far as the world is concerned, the Red Sea coral reefs are doing pretty well. The amount of coral cover ranges from 50-85% depending on the site being examined. However, not everything is rosy at the Red Sea. There has been significant damage done due to overfishing, and major damage done by irresponsible diving, driven by tourism. The Ras Mohammed National park was established off the coast of Egypt in 1983 to help combat the degradation of the reefs. More parks like this will be needed to created to help ensure the reefs safety.

Sources

1.http://www.coral-reef-info.com/red-sea-coral-reefs.html

2.http://www.natureasia.com/en/nmiddleeast/article/10.1038/nmiddleeast.2011.119

Hard Corals

This blog post will be focused on hard corals, and how these are very significant to the coastal system. Hard corals can just be healthy corals that's are naturally hard, but there is also an order of coral known as Scleractinia, which has a nickname called 'stony coral'. These occur in all the worlds oceans, and as suggested by their name, they are harder and more sturdy than other orders of coral. But why is this hard coral so important?

An example of a Scleractinia Coral.

The answer is that they provide a natural barrier against waves, which helps to protect global urban populations, coastal communities and the beach itself against erosion and water damage (such as flooding). The corals reduce the amplitude of the incoming waves by absorbing energy. The waves then have less erosionary power to cause damage. They act as a dampener against the waves. This ability of coral reefs to act as protection against waves will become even more important due to climate change. It is thought that the frequency and severity of storm events such as hurricanes are likely to increase. This will mean that more and more protection against storms will be required.

Governments spend billions on flood defence schemes the world over. Defra spent £2.56 billion between 2007 and 2011, and this figure is set to rise.

DEFRA Spending From 2006-2015

From the figure, we can see just how much DEFRA has been spending on flood defense. Spending reached a peak in 2010-2011, where it totaled almost £700 million. This is an astronomical figure, and without corals as a form of natural defence, who knows how much it could have been, or how much it will be in the future.

 We can see that so called 'hard engineering' is incredibly expensive, and perhaps other soft engineering techniques should be considered. The question is are soft engineering methods effective enough?

The protective nature of coral reefs assumes that they are healthy. They are no longer as effective at absorbing wave energy. This can be caused by acidification or even bleaching due to high temperatures. This means they are more likely to suffer damage from the waves as their structural integrity has been compromised. This can then result in more coastal erosion as they are then not as well equipped to protect the coastline.

Here we've had a brief look at how hard corals protect the coast. It may well be wise for governments to invest in promoting coral reef growth, as this will help coral populations to soar, as well as being less expensive than large man made structures such as sea walls, groynes and dykes.

Sources

1. Coral.org/blog/hard.corals.natures.seawalls/

2. https://www.google.co.uk/amp/s/www.carbonbrief.org/factcheck-how-much-is-the-government-really-spending-on-flood-defences/amp

Changes to the Great Barrier Reef

Changes to the Great Barrier Reef

A famous example of a coral reef, the Great Barrier Reef (GBR) is the largest in the world. It covers an approximate area of 133,000 square miles, composing 2900 individual reefs and 900 islands. It is famously so big, that it can be seen from space. 1981 was a big year for the GBR, as it was named a world heritage site, due to the sheer number and diversity of the wildlife supported by these reefs.

Great Barrier Reef at its best, showcasing all its diversity.

This was a massive boost for tourism and visits to the GBR, but in the prevailing 30 years or so, the area has been going through some tough times. On the 28^th November, BBC news reported that due to high water temperatures throughout 2016, 67% of corals had ‘died’ in the northern section of the GBR, as well as 6% from the central section. Despite this doom and gloom, some positive news from the southern part of the reef where the vast majority of the reef remains in good health. This was the worst ever recorded bleaching event in the Barrier Reef’s history and with global ocean temperatures set to rise, this may not be the largest bleaching event for long….

As well as rising temperatures, the GBR faces a threat from the declining amount of coral calcification. This is the result of increased ocean acidification. The level of coral calcification has decreased by 14.2% since 1990, the sample area encompassing 328 colonies from 69 reefs that make up the GBR. This is unprecedented in at least the last 400 years. The impact of a decrease in the amount of coral calcification means coral reefs lose their ability to deposit calcium carbonate (CaCO3). This is important as thousands of coral species derive their structural integrity from creating a calcareous skeleton. The peak year was 1970, where calcification was increasing by 1.76 gcm-2 year-1. It’s been downhill ever since.

And it continues to get worse. Kroon et al, 2012, published a paper stating extensive nitrogen, phosphorous and herbicides had been found throughout the GBR. 80000 tonnes of nitrogen now enters the GBR every year, with phosphorous at 16000 tonnes a year. These inputs into the GBR have come as a result of anthropogenic activity, especially from agricultural sources, urban development and deforestation. The danger of these inputs is that it may lead to eutrophication, hypoxia and reductions in coastal biodiversity. This will affect the coral as well, as the algal blooms will prevent coral from using photosynthesis to feed and will therefore begin to bleach.

As we have seen, the GBR has experienced some testing times, and now it is under threat like never before. The outlook doesn’t look promising, however hopefully there can be success built around the presently healthy southern part of the reef. In summary, coral populations have been on the decrease ever since 1970, due to a mixture of anthropogenic factors. In order to save the Great Barrier Reef concerted effort from Australia and other world powers will be required.

 

Sources

Full BBC article: http://www.bbc.co.uk/news/world-australia-38127320

http://science.sciencemag.org/content/323/5910/116.full (Glenn De'ath et al, 2009)

http://www.sciencedirect.com/science/article/pii/S0025326X11005583 (Kroon et al, 2012)

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