How does rising atmospheric CO2 affect marine organisms?

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Rapid Adaptation to Potential Effects of Climatic Change Via Natural Selection
Purcell, K.M., Hitch, A.T., Klerks, P.L. and Leberg, P.L. 2008. Adaptation as a potential response to sea-level rise: a genetic basis for salinity tolerance in populations of a coastal marsh fish. Evolutionary Applications 1: 155-160.

What was done
Noting that "relative sea-level rise is resulting in the intrusion of saline waters into marshes historically dominated by freshwater," the authors examined the effects of historical salinity exposure on the survival of Western mosquito fish (Gambusia affinis) of coastal Louisiana (USA), where they retrieved populations from fresh, intermediate and brackish marshes, assessed their survival time in water having a salinity of 25%o, and tested their descendents (reared for two generations in freshwater) to see if there was a genetic basis for any differential survival they might experience when introduced into brackish water.

What was learned
In the first phase of their study, Purcell et al. determined that "fish from brackish and intermediate marshes had an increased tolerance to salinity stress relative to fish from freshwater environments," while in the second phase they found that "descendents of individuals from brackish marshes showed elevated survival relative to the descendents of fish with no historical exposure to salinity."

What it means
The four researchers say the "difference in salinity tolerance among individuals that had never experienced elevated salinity strongly suggests a genetic basis for the differences observed between fish from brackish and freshwater marshes," and they conclude that "this genetic basis for increases in salinity tolerance to stress events suggests that at least some resident marsh fishes have the capacity to respond to saltwater intrusion through natural selection." And, we might add, they apparently have the capacity to so respond very quickly, i.e., in only a couple of generations.

Reviewed 13 May 2009