Final Blog

Over the course of these blogs I have learned a vast amount about corals, from how they function in the ocean system. On a smaller scale, I have looked at individual coral reefs in the form of the Great Barrier Reef and the Red Sea Coral Reef. I have seen how corals are affected by human stress, and just how large this problem is set to become.

Human stresses are a gigantic threat to corals. We have looked at this in detail. The future of the coral reefs hangs in the balance. Unfortunately the collective lack of action from world powers to tackle climate change leads be to believe that corals may be consigned to the history books. Bleaching of corals is increasing rapidly, co2 emissions are as well, resulting in an acidic ocean, and continued irresponsible fishing and dumping of waste into the ocean means corals look set to face an uphill battle for survival.

As David Attenborough said in the recent 'Planet Earth 2', humans are a plague on the earth. With little regard for the world we live in, we are destroying environments world over, with no thought of the cost. The loss of corals would be catastrophic, both economically and environmentally. The loss to the tourism would run into the billions of $. Arguably, the environmental impacts would be even more astronomical. The loss of corals would mean decrease in fish populations as well as other marine life. The lack of corals could lead to mass starvation as corals from the basis of the food chain with the support they give to algae.

There would likely be unforeseen impacts with the loss of corals. One certainty would be that coastal areas would come under a lot more stress from waves and storms. Corals act as a natural barrier and dissipate the energy of incoming waves. Without this other forms of protection would be required, such as expensive hard engineering methods. Damage to low lying countries would increase, like Bangladesh and The Maldives.

An example of the damage that can be caused by rising sea levels.

It seems as though there is not much hope for corals, but there is time. If global action can be taken to combat climate change, then perhaps there will be a future for coral reefs. We are the generation that can make a difference, and so we must work together to ensure the future of not just coral reefs, but the entire world.

Dependence on Corals

As we draw to the end of this blog series, I will look at just how important corals reefs can be, as we start to get used to the reality that they may no longer be around as we move into the future. The environmental and economic implications of the loss of coral reefs would be catastrophic.

Now, the complete loss of coral from the earth is far from certain and may not ever happen, but what is certain is their importance to so many people. It is estimated that 6 million people worldwide are dependant on coral reef fisheries. This may seem like a small number seeing as the worlds population now stands at over 7 Billion. But these people tend to live in very poor countries, and so the coral reefs and the fish that inhabit them are the only way to survive. The problem with all these people being so dependant on the fisheries is that overfishing has begun to be a problem. The lack of fish is making a poor area even worse off than before. There have been attempts to diversify where these areas get there income from, to reduce dependence on the coral reefs. This however has not been successful, and has in fact had adverse effects on communities.

Fishery

It seems as though it must be accepted that these 6 million people must rely on coral reefs, and least in some capacity. The corals don't just provide income for people oh no no no. They help to provide people with an identity, and add to people's lifestyle. This lifestyle is one that they may not have been able to chose, but at least these coastal areas have something in common, as they don't have much. The corals are something that a community can be built around, some,thing that is hard to quantify.

Although we don't directly rely on coral reefs directly in this country, their impact is till felt. Here in the UK, we buy fish from all over the world. The loss of corals would mean less fish. This would result in a massive increase in price. This is just an example of how interconnected the world really is.

We have seen that some areas of the earth are more dependant than others, but it is certain that no one wants corals to die out, as the impacts would be catastrophic and would be felt on a global scale.

Source

1.http://www.sciencedirect.com/science/article/pii/S1877343513001875

Current Status of Coral Reefs

Worrying news has come from a recent study by Hooidank et al, which suggests that coral bleaching is the greatest threat to coral reefs, and that by the end of the century, the majority of corals will unfortunately have gone past the ASB- Annual Severe Bleaching condition. This is where change is a certainty and recovery is not certain whatsoever.

The corals are bleached when temperature stresses get to too high a level. When this stress occurs, the zooxanthellae will leave the coral. If the temperature stresses continue, the coral will die. How long the coral can survive in this state will depend on the severity of the temperature stress, and the resilience of the genus of the coral. If the water conditions return to acceptable levels, then the coral may survive. Worldwide there has been an ocean bleaching event that began in 2014, and may continue further into 2017.

Anthropogenic activity is the main driver behind the temperature stress felt by the corals. Things are not looking good for the corals, with 99% of reefs experiencing annual severe bleaching. The average projected year for this event is 2043, so just 26 years into the future. There is just over a quarter of a century to make changes, however the damage may already be done.

http://www.nature.com/articles/srep39666/figures/1

Above is a link to the figure used in the report. No one ocean basin stands out as having particularly healthy or unhealthy reefs. However specific countries are in danger. For example, Papa New Guinea has a high proportion of their reefs that are likely to experience ASB events within the next 15 years (as early as 2030). This is very troubling as Papa New Guinea is not a wealthy nation, with a GDP per capita of just $2800, and so they may struggle to tackle issues such as coral reef preservation. The Northern area of the Great Barrier Reef is fairing slightly better, with the vast majority not likely to experience an ASB event until at least 2050. However, this only leaves 35 years or so to try and prolong the existence of corals in the ocean.

This is all very worrying, especially seeing as we have known about the decline in coral reef health for decades, and the problem is getting more severe and widespread. One strategy to prolong the lifespan of coral reefs is to manage the ‘weak of the strong’. This is the idea that attention and money be diverted to the healthiest coral reefs, while the unhealthiest in the oceans is left to die. This would ensure the future of at least some corals, preventing them from becoming extinct. The sad reality is that this may be the best we can do, with worldwide coral reefs a thing of the past.

The UN Framework on Climate Change Convention have met to try and prevent irreversible anthropogenic damage to the environment. They have 195 members, and have the goal of keeping warming below 2 degrees. This may be extremely problematic, but if global warming can be kept to 2 degrees, then there may be some hope for corals yet.

The growing acidity in the oceans is a problem also. It prevents corals from calcifying, which means they are not protected against the environment, as the calcification enabled them to have a protective layer.

Calcification Rates across the Great Barrier Reef

As we can see from the figure, calcification has decreased by 0.2 g/cm2/yr. over the last 100 years. This means that corals are now even more vulnerable than before. The most alarming conclusion that we can draw from this graph the rate of decline in the past 10 years. tTis shows that action is required now.

At this point I would like to speak about an example of corals becoming healthier, to counter the earlier part of the blog. Unfortunately I could find nothing along these lines. The only thing I could come across is information of how the rate at which corals are being destroyed is slowing down. This is as good as it gets. This was published in December 2016, so is extremely relevant, and just highlights the struggles faced by corals in the coming years.

 

 

Sources

1. http://www.nature.com/articles/srep39666

Man Made and Natural Stresses

In this blog post I will be looking at what has the larger impact on corals- natural or man made problems. Both can cause serious damage, with natural causes including hurricanes, large storms and natural algal blooms. Man made problems can be a wide variety of things- overfishing, ocean acidification, bleaching through increased temperatures as a result of global warming and other pollutants put into the ocean by humans.

First of all let's take a look at natural impacts on corals. Hurricanes are one such an issue for corals. They are unavoidable, and happen on a repeating time scale. They are very difficult to predict however. In 1980, Jamaica experienced a category 5 Hurricane, Hurricane Allen, around 40 years after the last major storm event. The storm was incredibly damaging to jamaicas corals. 5 years after the hurricane the number of corals per m2 was still lower that pre storm levels by a factor of 10. This just shows the catastrophic impact that hurricanes can have on coral reefs. The corals found at shallow depths were the most succeptable to damage. The elkhorn and staghorn corals were the worst off after the storm. These are examples of soft coral. The hard coral species fared better, as they are better equipped to be protected against storms. The corals at depths of 10-15m were much less likely to be damaged. This meant that after the storm the area was much more densely populated with hard corals relative to soft corals than before the storm. The storm also had a secondary impact on the coral. The hurricane resulted in an algal bloom. This algal bloom transpired as a result of increased runoff of nutrients following the high rainfall and windspeeds. This bloom prevented the coral from being able to feed, as this occurs through photosynthesis which was temporarily blocked by the algae.  

This meant that the recovery of the corals was inhibited. However over time they will be able to recover. The problem in recent times is that the human factors will then come into play once corals have been weakened by a hurricane for example, and put the corals under incredible strain.

There are several ways in which human activity puts corals under stress. As we all know, anthropogenic activity has resulted in global temperatures accelerating to new levels. These elevated temperatures will result in the loss of symbiotic algae from corals. This means they can no longer feed. The bleaching effect is he loss of the algae as this is what gives the coral its colour. Corals can recover from bleaching, but this requires the temperature of the ocean to go down. It is hard to

quantify how much bleaching has been due to human activity. It is clear however that human activity has had a significant impact on coral bleaching. Scleractinia and hydro corals are particularly succeptable to bleaching. It has been predicted that a 2 degree increase in the ocean temperature will reach the upper threshold of the majority of corals. This is a very worrying statistic.

Acidification is another threat to corals. Acidification can be caused by irresponsible farming and irrigation, resulting in the runoff of fertilisers. Acidification of the oceans can also be caused by extra co2 being in the atmosphere, caused by anthropogenic sources. This then results in more acid in rainwater, which will then filter into the oceans. This prevents corals from being able to produce their protective skeleton, leaving them vulnerable to waves and storms.

Overfishing is another human impact on corals. Overfishing results in man made algal blooms,mas there are less and less fish to eat the algae and phytoplankton. The algal blooms prevent the coral from being able to feed through photosynthesis.

But what has the bigger impact on corals? Both natural and human impacts can be destructive. Natural impacts tend to be much larger in their scale and intensity, over a much shorter period of time, such as the hurricane we examined in Jamaica. There was a large drop off in the amount of coral found after this very serious event. However this was a category five hurricane, and so the majority of hurricanes and tropical storms will be at a lower magnitude than this. Corals are also well adapted to recovering from tropical storms, and complications tend to arise from human sources.

Human effects on coral seem to be less intense than tropical storms, but they ever present. A storm may last a day or two, but ocean temperatures rising is a constant worldwide. With no signs of slowing down, it would appear that human impacts are the largest threat to coral the world over. The human impacts are something that we can do something about, which means the future of corals are in our hands.





Sources
1.http://bio.classes.ucsc.edu/bio160/Bio160readings/Catastrophes,%20Phase%20Shifts.pdf
2. http://link.springer.com/article/10.1007/BF00303779

Coral Reef Biodiversity

As we have seen in previous posts, corals have a mutually beneficial relationship with symbiotic algae, zooxanthallae. It is hard to quantify just how much bacteria is found on corals. This algae is not the only thing that can be found around reefs. They play host to a wide variety of fish, crabs, sharks and all manner of other sea creatures. Like rainforests on land, coral reefs are hotspots for biodiversity. The Pacific Ocean is home to a vast array of plant and animal species, encompassing areas such as Australia, Indonesia, The Pacific Islands etc. these contain a large proportion of the worlds coral reefs. The Great Barrier Reef has 600 species of coral, 1500 species of fish and 6 species of turtle alone. The marine life flocks to the corals.

As we know, these corals are under threat, and so as a result of this these animals and plants are under threat. If corals were to be eradicated from the face of the earth, then it would be likely that the marine life dependant on them will follow suit. It is not just the decline of coral that affects these species. Overfishing has been increasing rapidly, coupled with the disease and bleaching of corals has left many ecosystems in a sorry state.

A study by JM Pandolfi et al. showed just what has been happening to the diversity at coral reefs from prehuman times to the present day. An alarming number of large herbivores have become extinct in this time period, with almost 30% of the large herbivores perishing. This contrasts to small herbivores who experienced no extinction over the same period, however there was still a high proportion of coral reefs that had depleted amounts of both small and large herbivores. It is a different story with regard to the carnivores found at coral reefs. Only 10% of large carnivores became extinct, 20% less than herbivores. Looking to plants, seagrass has become depleted at 50% of studied sites. These are worrying statistics. This has been taken across the entire world so gives a fairly accurate portrayal of what is currently going on in the worlds coral reefs. Here is a link to the study:

https://www.researchgate.net/profile/Robert_Warner2/publication/10612648_Global_Trajectories_of_the_Long-Term_Decline_of_Coral_Reef_Ecosystems/links/0912f50883b8b8e52f000000.pdf?origin=publication_detail

This reduction in biodiversity will then add to the issues faced by corals. The lack of fish and other marine animals will result in algal blooms. This will reduce the amount of sunlight reaching the corals. The corals will struggle to feed, resulting in more bleaching. Bleached corals will attract less animals. There is a multiplier effect occurring. This is a dangerous cycle that needs to be broken.

Things may be different on a local scale but on the whole things aren't looking good. The decrease in biodiversity is set to increase, with coral bleaching set to rise, along with unsustainable fishing, the oceans may be a lonely place to be in the future.

Corals and Ocean Indicators

As we have seen in past blog posts, corals are extremely sensitive to changes in sea temperature, salinity and acid levels. This is normally seen as a negative, however there is an upside. The coral can be used as an indicator as to areas affected by climate change. The reason that they are so good at being ocean health indicators is that they are found worldwide, especially in the tropics, which are particularly susceptible to climate change. When there has been an increase in the ocean temperature, the corals will show this through bleaching. This is because when temperatures get too high, the bacteria that gives coral its colour will leave the coral as it cannot stand the temperature. The more bleaching that has taken place, the higher the relative temperature of the ocean will have become. Corals will show an increase in acidification by a reduction in calcium carbonate in the skeletons of the corals. The more CO2 that is dissolved into the ocean, the lower the amount of calcium carbonate corals will have. There is an inverse relationship. There are some issues with using coral to find out about ocean water quality. For example, changes in coral reefs may not represent global changes, and may just show local variations, and don't show the bigger picture. The good thing about them is that they are so well monitored that any changes that occur are usually observed and recorded on a large scale.

So we can see that corals can be used to determine ocean health, but what other methods can be used to evaluate the health of oceans?

One such method of determining ocean health could be by examining diatoms. These can be used to show water quality. This is because only certain diatom species will live in certain conditions. So if they are found in an area, then you can establish what the conditions in the ocean when the diatoms were alive. The sudden disappearance of a species will tell us something has changed.Diatoms are useful for this as they are extremely abundant, have large distribution and have a vast number of

species, which means they are easily identifiable. This means that diatoms are extremely useful at

telling us about ocean changes. They aren't quite as specific as corals at identifying changes, but used in conjuncture with corals they could be extremely useful.

An example of a diatom, which like zooxanthallae is microscopic.

Other indicator species can be used to show ocean quality. This can be invertebrate species such as caddis flys and nymphs that can be found in certain conditions. These invertebrate indicator species can be harder to sample than coral for example, as they require collection and are harder to count.

I think that coral are a fantastic indicator of climate change. The sensitivity to a variety of different factors means that they provide excellent detail to explain what is happening to the oceans. Used in conjecture with invertebrate indicators and diatoms, a clear picture of the oceans can be determined.

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