Ocean acidification and its impact on coral reefs

Ocean Acidification is: the ongoing decrease in the PH of the Earth's oceans, caused by the uptake of carbon dioxide (CO2) from the  atmosphere. Seawater is naturally slightly basic (meaning pH > 7).

Why Coral Reefs are important?

They act as a natural coastal barrier, they support Biodiversity, they are an habitat for third of all fishes at some point of their lives (!) , they are a food source and support the local economy by being a tourism site.  Also - many modern medical advances focus on marine organisms. 

Below is a reading section and a data graphs of the processes described in the reading section.
Please read the section and the accompanying graphs, and at the end answer the question.

Reading section: Ocean acidification and its impacts on coral reefs

Oceans play an important role in the natural carbon cycle by absorbing part of the carbon dioxide contained in the atmosphere. Calculations show that the oceans are responsible for absorbing half of the man-made emissions until 1994 and just 30% of the emissions since.

Ocean carbon dioxide absorption has another result - ocean water acidification. For the next 100 years the forecast shows a reduction of 0.5 to 0.3 pH units for the surface waters of the oceans.

A decrease in pH value ​​entails physiological consequences for various processes, especially on limestone skeleton-based organisms (carbonate). Skeletal construction rates of limestone reef-building corals have fallen in recent years due to rising concentrations of carbon dioxide in the oceans waters. Additionally, these chemical changes in the ocean are likely to weaken existing coral skeletons and reduce the growth of reefs. This phenomenon is called coral bleaching, because the dying corals loose there colors and turns white.

A new study describes a decrease of 13% in the rate of limestone skeletal construction since 1990 at the Great Barrier Reef in Australia - the world's largest reef. Researchers attribute it to a combination of two processes: ocean acidification and rising temperatures (rising temperatures harm corals in a different way than acidification).

Models predict that with a doubling of the concentration of carbon dioxide in the atmosphere, coral reefs will stop growing altogether, and instead begin to dissolve. This prediction is very gloomy, considering the rich variety of  marine species.

(This section was taken and edited from the article: "The effects of global climatic change on marine ecosystems: the global situation and the implications for the marine environment in Israel", by Gil Rilob and Haim Treves, the magazine "Ecology and Environment", January 2010, No. 1, (pp 65-57)) .

Coral Bleaching at the Great Barrier Reef

The Data Graphs :


Top graph (a):

Red - Hawaii

Black - Antartics

Bottom graph (b):

Dark green  blue - the Atlantic ocean

Light green  blue - the Pacific ocean

(The graphs are from a presentation "Climate Change in the Middle East of the 21st century - perception and reality," Prof. Yoav Yair, School of Sustainability, Herzeliya, a seminar Communication and Environment, 3rd of December 2015)

For more information watch the attached video :

Fuel, coal, oil and natural gas combustion are producing gases, which accumulate in the atmosphere, including carbon dioxide (CO2). The accumulation of these gases causes many changes on Earth, such as rising the temperature of the atmosphere, which impacts marine organisms such as coral reefs.

How does the increase of atmospheric carbon dioxide affect coral reefs?
1 People tried to answer this question

The increase of CO2 in the atmosphere increases the amount of CO2 dissolved in the oceans and causes an increase in the concentration of limestone materials that corals are made from.
The increase of CO2 in the atmosphere decreases the amount of CO2 dissolved in the oceans and thus affects the growth rate of corals.
The increase of CO2 in the atmosphere reduces the amount of CO2 dissolved in the oceans and thus affects the growth rate of corals.
The increase of CO2 in the atmosphere increases the amount of CO2 dissolved in the oceans and causes an increase in ocean acidity and reduces the skeletal growth rates of limestone corals.

1.  persits eugene (2020-05-20 16:00:00)
interesting choice!
Hi, Yasmine! 
After reading your question i found it very interesting.The question raises an issue that can affect our future, and not only for our country, but for whole world.
the wording of the question is very solid,full of useful data, that help to get to the right answer, but i think, that you can add a video, describing the bleaching coral process,
For example:

2.  Khawaled Nisreen (24.05.2016 pm 07.40.53)
coral bleaching
Hi for all,
The topic that your question talking about is very interesting and it is obviously related to our daily life. The question is written very well and it includes distracts answers and  an obvious  right answer. 
The reading section helps the reader to understand the question as also it is rich with information that are related to the question , the information depends on researches that makes it more interesting and relevant to our daily life.
The picture of coral bleaching is magnificent and shows the reader obviously the topic of the question , I think that there is no need to the graphs that you put , they are not clear beside the don't show the effect of CO2 on coral reefs.  
I recommend to you to put this video witch shows the effects of CO2 on coral reefs :

The points on map : 
let's start with the first point : The Atlantic ocean , this point shows only graphs, it needs explanation , I didn't understand how these graphs supposed to help me understanding the question. 
The second point : The inter-university institute for marine sciences in Eilat , this point includes information that related to the topic of the question , it talks about coral bleaching in Eilat , it means that it shows the reader in Israel he relevant of the question  to his  daily life beside it helps him to solve the question. 
The third point : Haifa Bay , this point is important and interesting, It shows the reader in Israel he relevant of the question  to his  daily life ,but I think that the text should be shorten  and the picture is needless, it will enough to explain about the effect of  refinery and factories on coral reefs .The video is amazing and it obviously explains the point. 
The fourth point : Eilat Bay , it was so amazing to know that the coral in Eilat has a tolerance for bleaching so it survives high temperatures . The information in this point helps the reader to solve the question. 

Nisren Khawaled 
3.  Ben-Menahem Yael (25.05.2016 pm 02.31.00)
My Opinion

Hi All,


I think that the subject you chose is very interesting, since it deals with an actual issue that is worldwide concern,

and the main cause of this issue is related to human impact.


I like graph number two that demonstrates the following dependencies: 

  • Co2 concentration in the ocean seawater over the years

  • PH value in the ocean seawater over the years.

I think that the student can deduce from it the  relation between the above two items –

when the CO2 concentration increase in the seawater, the PH value decreases.


I think that the following changes in the question  may contribute to the student's understanding:

1. Try to minimize the text and add more pictures that  demonstrate the phenomenon.

            • Picture of “before and after” the coral bleaching phenomenon

            • Picture of the natural carbon cycle that demonstrates how the CO2 "moves" from fossil fuels burning to the atmosphere and then absorbed by seawater in the ocean



 The picture shared under Creative Commons Licenses: http://www.visionlearning.com/img/library/modules/mid95/Image/VLObject-2637-031218011217.jpg

2. Divide graph 2 into two separated graphs

  • Co2 concentration in the ocean seawater over the years

  • PH value in the ocean seawater over the years.

3. From graph 2 the student can  understand that the increase in CO2 causes reduction in the PH value – You can omit the explanation about the PH reduction in the text.

4. Addition of Acidification definition may help the student to find the relation between acidification and reduction of the PH value.

5. Regarding the close question, it seems that both  following answers may be valid. 

A.      The increase of CO2 in the atmosphere increases the amount of CO2 dissolved in the oceans, resulting in

rising water temperatures which causes a decrease in skeletal construction rates at limestone corals.

B.      The increase of CO2 in the atmosphere: increases the amount of CO2 dissolved in the oceans,

causes an increase in ocean acidity and reduces the skeletal growth rates of limestone corals.

Assuming that the correct answer is B, answer A may still be valid, since it is known that the increase in CO2 is related to global warming that can raise the seawater temperature. In addition, as you showed, high temperature of seawater may also cause a decrease in skeletal construction rates at limestone corals.

Good Luck!


4.  Gadban Amal (29.05.2016 am 09.07.03)
why coral reefs is important?

hi all ,
first of all , you choose an interesting topic and presented  in an excellent manner.
Attached background is rich with materials and gives a direct answer to your question , I've never been interested in this subject before but after going through your station i wanted to know why coral reefs is so important and why should people take care of it?
so i recommends to add a paragraph on the importance of the coral

as we can see in the pic above the coral reefs benefit the economy ,
coral reefs suppoet commercial and subsistence fisheries as well as jobs and businesses through tourism and recration .
Approximately half of all federally managed fisheries depend on coral reefs and related habitats for a portion of their life cycles. The National Marine Fisheries Service
estimates the commercial value of U.S. fisheries from coral reefs is over $100 million.

Local economies also receive billions of dollars from visitors to reefs through diving tours, recreational
fishing trips, hotels, restaurants, and other businesses based near reef ecosystems.

refernce :

point in the map:
John Pennekamp Coral Reef State Park :
כתובת: 102601 Overseas Hwy, Key Largo, FL 33037, ארצות הברית
Coral Reef Scuba:
כתובת: 2784 Capital Cir NE # 2, Tallahassee, FL 32308, ארצות הברית
5.  Pearlstein Moran (30.05.2016 am 09.59.04)
Thanks for all the comments
Thanks for all the comments you all wrote us
We all liked the videos and decided to add the cartoon one.
We think that the text is as short as can be, and also we added an introduction on "why Coral reefs are important", and changed answer no.4.

History of edits
More Interactive Questions that might interest you In Biology