How does rising atmospheric CO2 affect marine organisms?

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Juvenile Marine Fish Learning to Take the Heat
Eme, J., Dabruzzi, T.F. and Bennett, W.A. 2011. Thermal responses of juvenile squaretail mullet (Liza vaigiensis) and juvenile crescent terapon (Terapon jarbua) acclimated at near-lethal temperatures, and the implications for climate change. Journal of Experimental Marine Biology and Ecology 399: 35-38.

The authors write that "temperate fishes have been considered especially vulnerable to changing climate conditions," and that "increasing water temperatures may also threaten shallow-water marine fishes inhabiting nursery environments, like tropical mangroves and seagrass beds." But is this really so? That is the question that drove them to perform new experiments designed to evaluate these hypotheses.

What was done
Eme et al., as they describe it, "used critical thermal methodology to quantify critical thermal maxima (CTmaxima) of juvenile squaretail mullet (Liza vaigiensis) and juvenile crescent terapon (Terapon jarbua) captured from shallow seagrass nursery areas around Hoga Island, southeast Sulawesi, Indonesia."

What was learned
The three US researchers report that groups of mullet that were acclimated to a constant temperature of 37°C, as well as temperature cycles of 35-39°C or 37-41°C, all displayed statistically similar mean CTmaxima of 44.7, 44.4 and 44.8°C, respectively. And they likewise found that terapon that were acclimated to a constant temperature of 37°C or a temperature cycle of 37 to 40°C both displayed mean CTmaxima of 43.8°C.

What it means
Eme et al. conclude, in their words, that "terapon and mullet demonstrate exceptional tolerance to high temperatures," and they say "it seems likely that shallow-water sea surface temperatures would have to be much higher to adversely affect these and other shallow water marine fishes (Eme and Bennett, 2009)," noting that these "exceptionally high CTmaxima afford mullet and terapon a significant measure of protection against changing habitat conditions." In fact, they write that "despite diverse independent origins across taxa, fishes may share a common suite of physiological adaptations allowing them to survive periodic exposure to high environmental temperature (Hochachka and Somero, 2002; Somero, 2010)," and that "exceptional thermal tolerance may be common throughout the biodiverse shallow waters of the Indo-Pacific." Thus, in the final analysis, they conclude that "tropical marine fishes inhabiting fringing nursery environments may have the upper thermal tolerance necessary to endure substantial increases in sea temperatures.

Eme, J. and Bennett, W.A. 2009. Critical thermal tolerance polygons of tropical marine fish from Sulawesi, Indonesia. Journal of Thermal Biology 34: 220-225.

Hochachka, P.W. and Somero, G.N. 2002. Biochemical Adaption: Mechanism and Process in Physiological Evolution. Oxford University Press, Oxford, United Kingdom.

Somero, G.N. 2010. The physiology of climate change: how potential for acclimatization and genetic adaptation will determine 'winners' and 'losers'. Journal of Experimental Biology 213: 912-920.

Reviewed 1 June 2011