How does rising atmospheric CO2 affect marine organisms?

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Agricultural Crops, the Herbivorous Pests that Feed on Them, and the Bigger Omnivorous Bugs that Eat the Pests
Coll, M. and Hughes, L. 2008. Effects of elevated CO2 on an insect omnivore: A test for nutritional effects mediated by host plants and prey. Agriculture, Ecosystems and Environment 123: 271-279.

What was done
In what they describe as "the first study that measured the effect of global atmospheric change on an omnivorous consumer," the authors explored the impacts of elevated atmospheric CO2 on the behavior and performance of an omnivorous bug (Oechalia schellenbergii, Heteroptera: Pentatomidae) and its prey, a polyphagous chewing herbivorous pest (Helicoverpa armigera; Lepidoptera: Noctuidae), feeding on pea (Pisum sativum) foliage grown in controlled-environment cabinets maintained at atmospheric CO2 concentrations of either 360 or 700 ppm.

What was learned
Coll and Hughes report that the H. armigera pests that fed on the elevated CO2-grown pea plants were significantly smaller than those that fed on the ambient CO2-grown pea plants, and that the bigger O. schellenbergii bugs that fed on them "performed best when fed larvae from the elevated-CO2 treatment," because the prey of that treatment "were smaller and thus easier to subdue." In fact, only 13.3% of the predation attempts made on the larvae that were fed ambient-CO2-grown foliage were successful, as compared to 78.2% for the larvae that were fed elevated-CO2-grown foliage.

What it means
In light of their findings, the two researchers concluded that "elevated CO2 may benefit generalist predators through increased prey vulnerability, which would put pest species under higher risk of predation." Consequently, and "since omnivory is widespread in agroecosystems," they argue that "yield loss to most pest species will be lower under elevated atmospheric CO2 levels, compared to the current condition," which is good news for agriculture and great news for the people who depend upon it for their survival, which is nearly all of us.

Reviewed 26 March 2008