Several weeks ago I posted an article which was very sceptical about ocean acidification.  After spending the last term writing this blog and researching ocean acidification, I will now attempt to explore some of their claims and see if there is any truth behind them.

One of their main claims was that ocean biodiversity will flourish under increasingly acidic conditions.  Whilst the last post I wrote suggested that some species of mussel and lobster will be able to survive in acidic oceans there has been no conclusive evidence to suggest that biodiversity will actually prosper.  In fact if you try searching species that will thrive in acidic waters in Google or Web of Science you get very few useful returns. However, if you search species which are threatened by acidifying waters the literature is vast.  As I have said previously, the species most at threat are those which calcify, due to dissolution and a shoaling of the carbonate and aragonite saturation horizon.  These species are often low down in the food chain, and so if they go extinct their predators will also be affected.  The evidence for dissolution is abundant, not only from scientific experiments but also just by looking at some of the world’s coral reefs. I posted this image before which shows how rapidly a shell can deform in acidic water. 

This cartoon shows the deformation of a shell in an acidic ocean over a period of 45 days (NAOO).

Anthony et al. (2011) created a model to see how ocean acidification affected the resilience of coral reefs.  Their main findings were that reefs which suffer from overfishing and eutrophication were more vulnerable to acidic waters.  They also found that as CO₂ levels rise, the resilience and growth rates of coral reefs will fall and mortality will increase.  The Great Barrier Reef has seen a rapid reduction in calcification rates and growth of large corals (Hoegh-Guldberg, 2009).  Hoegh-Guldberg (2009) has also shown that ocean acidification not only reduced the productivity of corals but also made them more sensitive to bleaching.  More recent work by Kurihara et al. (2008) and Mayor et al. (2007) has shown that ocean acidification reduces egg production in marine shrimps and also causes an increase in unsuccessful hatchings in copepods.  Earlier on in this blog I also pointed out larger marine animals were being affected by ocean acidification.  Whale numbers are falling due to an increase in ‘noise’ in acidic waters, which makes communication and navigation trickier.  Clown fish are losing their sense of smell, due to the acidic conditions, which means that they can’t smell their habitats. 

I believe that we cannot deny the fact that ocean acidification is having a detrimental impact on marine organisms.  The effects are most widely felt by calcifying organisms yet larger marine mammals such as Whales are not out of harm’s way.  Caution needs to be given and some people probably over emphasise the effects of ocean acidification, as it is evident that some species can prosper in acidic waters. However, if their prey cannot adapt and goes extinct then they will die too, whether they are adapted to acidification or not.  More work needs to be done to assess the impact of rising CO₂ levels on a wider range of species to see how many other species have been able to adapt.  A significant proportion of ocean species will be affected by ocean acidification but it cannot be claimed that every species will be negatively affected.  Similarly, at the moment the evidence is too large to suggest that creatures are unscathed from rising carbon dioxide levels.

References

Anthony, K, Maynard, J. Diaz-Pulido, G. Mumby, P. Marshalls, P. Cao, L. (2011). ‘Ocean acidification and warming will lower coral reef resilience’, Global change biology, 17, 1798-1808.

Hoegh-Guldberg, O. (2009). ‘Climate change and coral reefs: Trojan horse or false prophecy?’, Coral Reefs, 28, 3, 569-575.

Kurihara, H. Matsui, M. Furukawa, H. Hayashi, M. Ishimatsu, A. (2008). ‘Long-term effects of predicted future seawater CO2 conditions on the survival and growth of the marine shrimp Palaemon pacificus’, J Exp Mar Biol Ecol , 367:41–46.

Mayor, D. Matthews, C. Cook, K. Zuur, A. Hay, S. (2007). ‘CO2-induced acidification affects hatching success in Calanus finmarchicus’, Mar Ecol Prog Ser, 350:91–97.