November 30, 2010

CO2 is Sustenance for Seaweed

Filed under: Adaptation, Plants

Americans continue to fall in love with sushi—even the smallest towns far away from metropolitan areas somehow are providing tasty bits of sushi to local customers. Sushi has gone from upscale and trendy to a popular and substantial component of American’s food intake. From fast food sushi to high-end restaurants to sushi at the ballpark, sushi is now everywhere!

Many of the items at a sushi restaurant contain any number of varieties of seaweed, and several days ago, someone asked us if seaweed benefits from elevated concentrations of carbon dioxide (CO2). We promised to look into the question and found several articles in leading journals that bring us all good news about the future of seaweed plants we love to eat.

The first article we discovered was published in Aquaculture by a scientist with China’s Shantou University; Zou notes that “This study was supported by the National Natural Science Foundation of China, the Chinese b863Q project, and Guangdong Natural Science Foundation, and Science Technology Bureau.” It seems that organizations in China have some keen interest in finding out how seaweed will perform in a world of higher levels of CO2?

Zou examined how elevated CO2 concentrations in water will impact one of the most economically important seaweeds—Hizikia fusiforme. For a bit of background on Hiziki, as it’s commonly called, what better place to look than an organic food store:

Hiziki is a dark brown, bushy plant that grows in the pristine coastal arctic current seas off the eastern shore of Japan. Hiziki needs plenty of sunshine, clean water and years to mature. Hiziki has long thick branches that stand straight in the water, like hair floating upwards. At the top of the stems or branches are smaller branches, much thinner than the main stem. On these smaller branches near the surface grow small, thick, pointed blades that resemble pine needles.

These needles are what folks crave, but the stems and branches are wonderful as well. Hiziki is very rich in minerals and has been a traditional part in the Eastern diet for hundreds of years.

Now, back to the science.

Zou collected the plant material at low tide in February along the coast of China’s Nanao Island (if you can point to Nanao Island on a map, you are in a very small minority of Americans). The plants were reestablished in their new home in aquariums with near ambient (360 ppm) and elevated (700 ppm) CO2 levels. The plants were measured regularly to establish the biomass and relative growth rate. A seen in Figure 1, the relative growth rate of the plants was 50% higher when grown in the water with elevated CO2 concentrations. The author notes “that prolonged exposure to the elevated levels of CO2 in seawater increased the growth rate of H. fusiforme.” The findings were viewed as similar to what others had found when they conducted various experiments on elevated CO2 and seaweed.

Figure 1. Relative growth rate (RGR) of H. fusiforme cultured with non-enriched (Air, averaging 360 ppm CO2) and CO2-enriched air (+CO2, averaging 700 ppm CO2). Vertical bars represent standard deviations of the means (from Zou, 2005).

A second article on this subject was published in Plant, Cell and Environment by three scientists from Scotland’s University of Dundee and the Scottish Crop Research Institute. As an introduction, Kübler et al. note that “Reviews of the large number of studies on the effects of increased atmospheric [CO2] on primary productivity have concluded that, on average, a doubling of atmospheric [CO2] results in an enhancement of growth rates of C3 plants by 40% and of C4 plants by 20%”. This should be good news for sushi lovers if they were concerned about the rice they enjoy—rice is a C4 plant and hundreds of studies have shown that rice will benefit enormously from elevated levels of atmospheric CO2.

Back to the seaweed. Kübler et al. focused on a bright red seaweed Lomentaria articulate; they collected the plant material from Fife Ness in the UK. The plants were then grown in water with CO2 concentrations maintained at 235, 350, 700, and 1750 ppm. They found that the “growth rate based on wet biomass was low or negative at [CO2] below the growth optimum and there was no effect of experiment date”. No problem here—we certainly do not expect the CO2 levels to decline any time soon. Kübler et al. importantly note “The mean growth enhancements due to changing [CO2], assuming no effect of [O2], were +314% and +50% at [CO2] of 2× and 5× ambient levels, respectively.”

OK—we think you get the message. Just like so many plants on the terrestrial earth that benefit enormously from elevated concentrations of CO2 (like trees, agricultural crops, grasslands), we find that plants in the sea similarly gain tremendously as CO2 levels increase. As seen in the Kübler et al. study, the effect will be particularly large over the next 100 years as concentrations of CO2 will very likely double.

So it is back to the sushi bar knowing that the rice will be better off in the future, the seaweed will be better off in the future, the edamame beans will be better off in the future, and … there is a pattern here. The answer to the question is definitely YES—seaweed loves elevated levels of CO2!


Kübler, J.E., A.M. Johnston, and J.A Raven. 1999. The effects of reduced and elevated CO2 and O2 on the seaweed Lomentaria articulate. Plant, Cell and Environment, 22, 1303-1310.

Zou, D. 2005. Effects of elevated atmospheric CO2 on growth, photosynthesis and nitrogen metabolism in the economic brown seaweed, Hizikia fusiforme (Sargassaceae, Phaeophyta). Aquaculture, 250, 726-735.

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