As the air's CO2 content rises in response to ever-increasing anthropogenic CO2 emissions, and as more and more carbon dioxide therefore dissolves in the surface waters of the world's oceans, theoretical reasoning suggests the pH values of the planet's oceanic waters should be gradually dropping. The IPCC and others postulate that this chain of events, commonly referred to as ocean acidification, will cause great harm -- and possibly death -- to marine life in the decades and centuries to come. However, as ever more pertinent evidence accumulates, a much more optimistic viewpoint is emerging. This summary examines the topic of the potential impacts of ocean acidification on fish.
In an early review of the subject, Ishimatsu et al. (2005)1 write that fish "constitute a major protein source in many countries," adding that the "potential reduction of fish resources by high-CO2 conditions due to the diffusion of atmospheric CO2 into the surface waters ... can be considered as another potential threat to the future world population." And in response to this selfexpressed concern, they conducted a survey of the scientific literature with respect to the potential negative consequences of atmospheric CO2 enrichment for the health of marine fish that could arise from continued anthropogenic CO2 emissions.
Focusing on the possible threat of hypercapnia-a condition that is characterized by an excessive amount of CO2 in the blood that typically results in acidosis, which is a serious and sometimes fatal condition characterized in humans by headache, nausea and visual disturbances-they say their survey revealed "hypercapnia acutely affects vital physiological functions such as respiration, circulation, and metabolism, and changes in these functions are likely to reduce growth rate and population size through reproduction failure." Although this potential threat sounds dire, it represents an egregious flight of the imagination in terms of what could realistically be expected to happen anytime to fish in Earth's future. Ishimatsu et al. report, for example, "predicted future CO2 concentrations in the atmosphere are lower than the known lethal concentrations for fish," noting "the expected peak value is about 1.4 torr [just under 1850 ppm CO2] around the year 2300 according to Caldeira and Wickett (2003)."