This is exactly the result which was seen when human food crops were grown under conditions of elevated CO2 - yes, they grew faster and had better yeilds - BUT the nutritional value decreased, making the resulting foods closer to being "empty calories": increased quantity, decreased quality.

News Release

10 February 2009

Netherlands Organization for Scientific Research

Climate change reduces nutritional value of algae

http://www.nwo.nl/nwohome.nsf/pages/NWOA_7P5BKH_Eng

Micro-algae are growing faster under the influence of climate change. However, the composition of the algae is changing, as a result of which their nutritional value for other aquatic life is decreasing. And because algae are at the bottom of the food chain, climate change is exerting an effect on underwater life. This is the conclusion of researchers from the Netherlands Institute for Ecology (NIOO-KNAW) and the Universiteit van Amsterdam.

Dutch researchers wanted to know whether an increased CO2 concentration exerted an influence on underwater life. They therefore examined freshwater micro-algae: small, floating and mostly unicellular algae. The experiments were performed in large tanks called limnotrons. These were aerated with ordinary air or with air containing an elevated concentration of CO2. The researchers then examined the ratio between the important elements carbon, nitrogen and phosphorous.

First link in the food chain

The micro-algae grew faster at a higher CO2 concentration, exactly as the researchers had expected. Yet this growth was also associated with a change in the composition of the algae. The algae cultured at a higher CO2 concentration contained relatively more carbon and relatively less phosphorous. This meant a reduction in the nutritional value, which could have detrimental effects upon the small animals that eat the algae such as water fleas. These in turn form food for fish, for example. As they are the first link in the underwater food chain, the algae ultimately influence the entire ecosystem.

In a follow-up study, the Centre for Limnology (NIOO-KNAW) and the Department of Aquatic Microbiology at Universiteit van Amsterdam will examine what effects the reduced nutritional value of the algae can have in real ecosystems. Meanwhile, it is already clear that the effects can become more pronounced as a result of higher water temperatures.

The best-known effects of climate change are shifts in the habitats of animals and plants, for example, species that spread further northwards. This research has shown that climate change can also exert significant effects on the underwater food chain.

This research was funded within the Water programme of the NWO Division for Earth and Life Sciences. (link: http://www.nwo.nl/nwohome.nsf/pages/NWOP_679KGZ_Eng)