Scientists Monitor Seaweed As CO₂ Changes At Biosphere 2

"We've catalogued 50 species in there and it's really not much bigger than an Olympic-size swimming pool," Glenn said during a recent visit to the facility in Oracle, Ariz., operated by Columbia University.

"We are trying to understand what maintains such a high species diversity, which occurs not just in Biosphere 2 but in the world's seas in general," he continued. "Wherever you look on tropical reefs, you don't find just a few species of algae, you find dozens."

Glenn's work on seaweed and other types of algae fits into a larger effort at Biosphere 2 to document how changing carbon dioxide levels influence marine life.

To compare algae growing under different carbon dioxide levels, Glenn takes random samples by throwing beachball-sized rings into the water and then collecting the algae within them when they land on the ocean floor. His team will also be collecting the animals in the rings to assist Richard C. Brusca, who is preparing to launch his own project. Brusca is director of education programs at Columbia University's Biosphere 2 and an adjunct faculty member with the UA department of ecology and evolutionary biology.

Carbon dioxide levels in the miniature ocean are manipulated every couple months, Biosphere 2 marine biologist Francesca Marubini said.

Scientists switch from low glacial concentrations to the concentrations typical of modern-day oceans -- and finally to the higher levels projected for the future.

Carbon dioxide is taking some heat these days because global temperatures appear to be increasing in sync with carbon dioxide's growing presence in the atmosphere. Ocean surface concentrations mirror atmospheric levels, which are expected to double over the next century.

Some believe algal bursts of productivity could hold some promise for slowing the rise of carbon dioxide levels.

"It's the seaweed and algae that actually have the most biological effect on the ocean carbon cycle," Glenn said, compared to other marine species.

As plants, algae grow by converting carbon dioxide into carbon compounds -- or what we as consumers call carbohydrates. Coralline red algae and some of its brethren also convert carbon dioxide into rock-like calcium carbonate, which builds reefs.

A lack of carbon dioxide can limit plant growth. This factor may have contributed to Glenn's observation that the coralline red algae in Biosphere 2 were looking decidedly pasty while living with carbon dioxide concentrations reminiscent of glacial times, about half of today's levels.

The red algae were back in the pink during Glenn's April visit, although not quite as vibrant as before the switch.

"Certainly the algae are not as happy as they can be," Glenn said. "It could seriously be that the carbon dioxide level was too low."

Yet they may not fare much better in the futuristic scenario, when carbon dioxide levels will be increased to about twice modern levels.

Research at Biosphere 2 and in other locations indicates that higher levels can bring their own problems, at least for the coral reef systems in which many algae thrive, as described in the April 2 issue of Science.

Recent experiments have shown that reef growth is reduced when carbon dioxide levels are high. Reefs grow as the plants and animals (especially corals) that live in them deposit calcium carbonate from their skeletons. A net rate of growth is essential on reefs to withstand the ongoing erosion by waves and ocean currents, Marubini noted.

On the other hand, many land plants are more productive given higher carbon dioxide levels. So it's possible the algae will do more work to counteract the reef's increased susceptibility to erosion.

It would be difficult to predict the various effects without the type of research that can be done in controlled conditions like those at Biosphere 2, Glenn noted.

Glenn and other researchers hope to shed light on some of the questions regarding algal productivity and the effects of carbon dioxide levels on marine life. This, in turn, could help policy-makers more rationally consider whether they want to continue the ongoing experiment of raising carbon dioxide levels in Biosphere 1 -- the Earth.

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Science contacts: Ed Glenn, UA Environmental Research Lab, 520-626-3322, eglenn@ag.arizona.edu
Richard Brusca, Biosphere 2, research department, 520-896-6408, rbrusca@bio2.edu
Francesca Marubini, Biosphere 2, research department 520-896-6408, fmarubini@bio2.edu
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Writer: Melanie Lenart of The University of Arizona
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Visit the UA Environmental Research Lab web page at http://ag.arizona.edu/azaqua/erlhome.html
Visit Columbia University's Biosphere 2 web page at http://www.bio2.edu
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