Ocean acidification and warming

There is no doubt that the increasing amount of greenhouse gases has changed global atmospheric temperatures.  Additionally the release of carbon dioxide into Earth's atmosphere has caused problems for oceans. Carbon dioxide can be released in many ways like burning fossil fuels, deforestation, and forest fires, etc.  About a quarter of all carbon dioxide emissions are absorbed by the oceans.  Within the past 250 years, the oceans have absorbed 530 billion tons of carbon dioxide, which was enough to produce a 30% increase in ocean acidity [9].

So you might be wondering...how does carbon dioxide translate into an increase in hydrogen ions?  What happens is carbon dioxide dissolves into water and reacts with the water, H2O.

[CO2] + [H2O] <==> [H2CO3]

Carbonic acid, H2CO3 is a weak acid so it readily donates a proton and releases HCO3-.  The proton H+ lower the pH and acidifies the ocean.
It is also important to note that as the concentration of carbon dioxide increases in the atmosphere so too does the concentration of carbon dioxide in the ocean because of Le Chatelier's principle of equilibrium. It is natural that chemical compounds want to be in balance.

The low pH prevents abalone shells from developing normally and erodes them.  Abalone shell is made of calcium carbonate tiles stacked like bricks, which makes them extremely strong.  Unfortunately acidification of ocean waters due to anthropogenic carbon dioxide is predicted to result in deleterious effects for abalone larvae development.  The culmination of these effects could be extinction within the next 100 years.  Acidic marine environments reduce the availability of carbonate ions required for shell construction [9].  Shells are very important for larvae and juveniles because they support and protect the young bodies. 

In a study done by Bryne et al., Haliotis coccoradiata reared from fertilization in temperature and pH treatments revealed that acidification to pH 7.6-7.8 resulted in unshelled larvae and abnormal juveniles.  This species of abalone is found in southeastern Australia where the ocean is warming several times faster than the global average, therefore referred to as a climate change hotspot.  The data for this study was collected from Little Bay near Sydney, Australia.  Bryne et al. found that pH and temperature changes did not interact with each other. The nine different treatments used three pH and three temperatures.  H. coccoradiata were observed at 21 hours, the time when normal abalone should have a well-developed shell [1].

In Figure 2, we can see that each two degree increment in temperature reduces the percentage of calcified/shelled abalone larvae.  Within each temperature treatment, the white bar representing the control pH 8.2 shows the highest percentage of calcified larvae.  The black bar representing the lowest pH of 7.6 is the shortest bar in each temperature treatment.  What is shocking is that even at the control pH of 8.2, the 4 degree Celsius increase affected abalone larvae development dramatically, causing the amount of normal larvae to drop to 20%.  At pH 7.6 and +2 and +4 degrees Celsius, most larvae were dead or severely abnormal.  Some individuals at control temperature and pH 7.8 appeared to be anatomically normal except for the absence of a shell, but transferring to control sea water for 3 days did not result in formation of a shell.  This shows that pH is crucial during the first 21 hours of larval development [1].

Neuman-Keul's post hoc tests indicated that the percentage of calcified larvae was significantly lower in the pH 7.6 and 7.8 treatments and in the +2 and +4 degrees Celsius treatments compared with controls [1].

These findings are important in addressing the near-future effects of ocean warming and acidification we will be confronted with if nothing is done to reduce man-made damage to our environment.  Ocean waters are projected to decrease in pH by 0.4 units by 2100 and 0.7 units by 2300.  Ocean temperatures are projected to increase 1-2 degrees Celsius by 2030 and 2-3 degrees Celsius by 2100 [1].  Lack of awareness and action will surely lead to reaching these projections and end in loss of marine biodiversity.

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