Talmage, S. C., & Gobler, C. J. (2010). Effects of past, present, and future ocean carbon dioxide concentrations on the growth and survival of larval shellfish. Proceedings of the National Academy of Sciences of the United States of America, 107(40), 17246. Retrieved from http://search.proquest.com/docview/757190173?accountid=10598
Anthropogenic CO2 has found its way into the world’s oceans, thereby decreasing pH levels. As a result, the growth of marine organisms, especially those with CaCO3 shells, is being negatively affected. The School of Marine and Atmospheric Sciences at Stony Brook University has conducted experiments that examine the effects of the ocean’s past, present, and future (21st and 22nd centuries) CO2 concentrations on the growth of larvae of two species of bivalve shellfish (Mercenaria mercenaria and Argopecten irradians). For these species, the CaCO3 shells, serving as lines of defense for larvae and providing physical stability for fragile organs, are so vital. Larvae of both species were grown under near preindustrial CO2 concentrations and modern day CO2 levels. The results show that for the former, growth and metamorphosis rates and survival and lipid accumulation rates were higher in comparison to the latter group of larvae. Thus ocean acidification during the past 200 years may be inhibiting the survival of larval shellfish.
At first, it might seem like a good thing that the oceans are absorbing massive amounts of carbon dioxide—about a quarter of all anthropogenic CO2 emissions. I mean, it’s slowing down global warming right? Not so fast. What many don’t realize is that even though the oceans are delaying atmospheric climate change, beneath the surface, dissolved CO2 causes enormous problems. Carbon dioxide forms carbonic acid when it dissolves in water, and the average acidity of ocean water has decreased from a pH of 8.2 to pH 8.1 since the Industrial Revolution. It may not seem like much, but because the pH scale is logarithmic, this 0.1 point decrease represents a 30% increase in the acidity of our oceans.
This increased acidity caused by our fossil fuel addiction means that we’re putting millions of aquatic species at risk. The situation is particularly worrying for species that use calcium carbonate to build their skeletons or shells, because the ability for these calcifying organisms to build their shells depends on the chemistry of the water they live in. These organisms range from phytoplankton, zooplankton and corals to molluscs, echinoderms and crustaceans. While there are exceptions, many studies of these organisms have found that an increase in dissolved CO2 and a decrease in pH results in decreases of average calcification rates and shell weights.
If this doesn’t seem like a big deal, then you should know that not only could this have rippling effects throughout oceanic ecosystems, but humans will be affected too. Or rather, humans are already feeling the effects, because ocean acidification has already reached economically important aquatic species. In 2007, oyster farmers in the Pacific Northwest discovered that their oyster larvae were dying like they had never seen before. The cause? The ocean water that the farmers used for their oyster tanks was so acidic that larvae shells were actually dissolving in it.
At one Washington farm, a shocking 80% of its oyster larvae died in 2009. The problem is particularly bad in the Pacific Northwest because of natural upwelling patterns, which brings up CO2-saturated water absorbed by the Pacific Ocean 50 years ago. Yes, you heard right. Water from 50 years ago, when CO2 emissions were much lower than they are today, is killing shellfish. Imagine how damaging the situation could become when the CO2 absorbed now resurfaces 50 years in the future.
In 2007, the total mollusc harvest is estimated to have been worth $15 billion. Some populations are especially dependent on shellfish— for example, New Zealand, Thailand, France and Chile rely on molluscs and other shellfish for over 10% of their protein. The subsistence fishers of small tropical island nations are even more vulnerable to changes in shellfish populations. Clearly, we should be concerned that our CO2 emissions are putting lives and livelihoods at risk through ocean acidification. If we don’t take action immediately, we’ll be harming more than just ocean life—humans will be feeling the effects as well.