How does rising atmospheric CO2 affect marine organisms?

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Atmospheric CO2 Enrichment and Mosquito-Born Diseases
Tuchman, N.C., Wahtera, K.A., Wetzel, R.G., Russo, N.M., Kilbane, G.M., Sasso, L.M. and Teeri, J.A. 2003. Nutritional quality of leaf detritus altered by elevated atmospheric CO2: effects on development of mosquito larvae. Freshwater Biology 48: 1432-1439.

We often hear climate alarmists predicting a great increase in mosquito-born diseases, such as malaria and yellow and dengue fever, as a highly-to-be-feared consequence of CO2-induced global warming. As noted by Reiter (2001), however, this claim has little foundation in either logic or real-world data. What is more, the paper of Tuchman et al. describes a previously unappreciated phenomenon that tends to mitigate against this ill-founded climate-alarmist contention.

What was done
The seven researchers (1) took leaf litter from Populus tremuloides (Michaux) trees (the most abundant tree species in Michigan, USA, where the work was conducted) that had been grown out-of-doors in open-bottom root boxes located within open-top aboveground chambers maintained at atmospheric CO2 concentrations of either 360 or 720 ppm for an entire growing season, (2) incubated the leaf litter for 14 days in a nearby stream, and (3) fed the incubated litter to four species of detritivorous mosquito larvae to assess its effect on their development rates and survivorship.

What was learned
Tuchman et al. report that larval mortality was 2.2 times higher for Aedes albopictus (Skuse) mosquitos that were fed leaf litter (and the bacteria that developed on it in the stream) that had been produced in the high-CO2 chambers than it was for those fed litter that had been produced in the ambient-air chambers. In addition, they found that larval development rates of Aedes triseriatus (Say), Aedes aegypti (L.) and Armigeres subalbatus (Coquillett) were slowed by 78%, 25% and 27%, respectively, when fed litter produced in the high-CO2 as opposed to the ambient-CO2 chambers, so that mosquitoes of these species spent 20, 11 and 9 days longer in their respective larval stages when feeding on litter produced in the CO2-enriched as compared to the ambient-CO2 chambers. As for the reason behind these observations, the researchers suggest that "increases in lignin coupled with decreases in leaf nitrogen induced by elevated CO2 and subsequent lower bacterial productivity [on the leaf litter in the water] were probably responsible for [the] decreases in survivorship and/or development rate of the four species of mosquitoes."

What it means
In the words of Tuchman et al., "the indirect impacts of an elevated CO2 atmosphere on mosquito larval survivorship and development time could potentially be great," because "longer larval development times could result in fewer cohorts of mosquitoes." And, it would stand to reason, fewer cohorts of mosquitoes should result in lower levels of all mosquito-born diseases.

Reiter, P. 2001. Climate change and mosquito-borne disease. Environmental Health Perspectives 109: 141-161.

Reviewed 31 January 2007