Study Sees an Advantage for Algae Species in Changing Oceans
Contrary to expectations, a microscopic plant that lives in oceans around the world may thrive in the changing ocean conditions of the coming decades, a team of scientists reported Thursday.
The main threat to many marine organisms is not global warming but ocean acidification, as carbon dioxide from the air dissolves into the water and turns into carbonic acid. Acid dissolves calcium carbonate in the skeletons of corals, for example; many scientists fear that acidification of the oceans will kill many, if not most, coral reefs by the end of the century.
Similar concerns have been raised about coccolithophores, single-cell, carbonate-encased algae that are a major link in the ocean food chain. Earlier experiments with a species of coccolithophore, Emiliania huxleyi, had found that lower pH levels (more acidic) hindered the algae’s ability to build the disks of carbonate that form its shell.
In Friday’s issue of the journal Science, however, scientists led by M. Debora Iglesias-Rodríguez of the National Oceanography Center at the University of Southampton in England and Paul Halloran, a graduate student at the University of Oxford, report that they found the exact opposite. The algae grew bigger in the more acidic water.
Dr. Iglesias-Rodríguez said the conflicting findings probably arose from differences between how the experiments were conducted. In the earlier work, the researchers lowered the pH by directly adding acid to the water.
In the work reported in Science, the scientists added the acid indirectly by bubbling carbon dioxide into the water, which more closely mimicked the chemical reactions that are occurring in the oceans. As a consequence, in addition to the lowered pH, levels of carbon dioxide in the water also rose — speeding up the algae’s photosynthesis machinery — as did the levels of bicarbonate ions, the building material for the carbonate disks.
The pH scale, which measures the concentration of hydrogen ions, runs from zero, the most acidic, with the highest concentration of ions, to 14, the most alkaline, with almost no ions. Ocean water today is somewhat alkaline, at 8.1, down from 8.2 at the start of the Industrial Revolution two centuries ago.
The laboratory findings agree with what has been observed in the oceans. Over the past 220 years, the average mass of a coccolithophore increased 40 percent as ocean pH levels dropped.
The hopeful news for coccolithophores, however, does not overturn the gloomy predictions for corals or negate ocean acidification as an impending ecological disruption, Dr. Iglesias-Rodríguez said. Rather, she said, it points to how little data biologists currently have. source
My comment: That article is rather interesting. First it shows how little we know about processes in the Nature in complex systems. My second thought is that this study doesn't show the upper limit of this process, because the algae cannot increase incessantly- first because the acidity will start hurting the living organism and second, because processes in Nature usually are inter-regulating themselves-so if one process gets too flourishing that could harm the whole ecosystem. Or it could not. The problem is that the study doesn't talk about the whole ecosystem and the limits of the process, in which its productive and in which it becomes harmful. But the over-all article is positive, especially as for the use of algae for alternative fuel. And again-there is the word SOME plankton types!
Some Plankton Thrive With More CO2
Most concerns about growing emissions of carbon dioxide have focused on the gas’s heat-trapping effect on climate. But ocean experts have increasingly warned that the direct chemical impact on marine life, as carbon dioxide dissolves in water and lowers its pH, could profoundly disrupt ecosystems by interfering with the growth of reefs and shell-forming plankton.
Now, though, a new laboratory study has shown that some types of plankton thrive in water with a low pH created by greatly raising concentrations of carbon dioxide. The plankton that demonstrated this unexpected ability are certain coccolithopores, single-celled plants that are sheathed in Frisbee-like plates rich in calcium. They are a cornerstone of ocean ecosystems and play a significant role, as they die and sink, in taking carbon out of circulation and locking it away in rock.
The study, led by Debora Iglesias-Rodriguez of Britain’s National Oceanography Center, was published today in Science Express, the online edition of Science.
It focused on laboratory tests in which coccolithophores were grown in water made more acidic by infusing it with bubbles of air with elevated concentrations of carbon dioxide. But the study also assessed long-term records of changes in the mass of the individual calcium plates, or coccoliths, which accumulate on the sea bed. Here’s what the researchers found:
“Field evidence from the deep ocean is consistent with these laboratory conclusions, indicating that over the past 220 years there has been a 40-percent increase in average coccolith mass. Our findings show that coccolithophores are already responding and will probably continue to respond to rising atmospheric CO2….”
The researchers, noting they only looked at one species, said the work suggests that the organisms could double their rate of photosynthesis and calcium uptake in carbon dioxide concentrations around double the current level of 380 parts per million. They stressed this was a rough projection and did not account for a vast range of variables in ocean conditions to come.
The take-home message is that while the long-term picture is clear, many details still require a lot more study. Europe is readying a fresh look at coccolithophores and pH.
In a commentary in Science Express on the new study, Victoria A. Fabry, a biologist at California State University, San Marcos, said the work illustrated the level of complexity of ocean ecosystems and the importance of developing standard approaches to such studies so results can be compared:
The diverse pattern of poorly understood biotic responses to ocean acidification found thus far makes it problematic to reliably predict the ecological and biogeochemical changes that will result from continued oceanic uptake of anthropogenic CO2. As atmospheric CO2 levels continue to rise, we are embarking on a global experiment with as yet uncertain long-term consequences for many marine calcifiers.
Dr. Chris Langdon, assoc. professor marine biology and fisheries, University of Miami, said he wanted to see more detail on the experimental methods than could fit in the short paper:
1) I don’t know what to make of these results. The short format of Science articles means that a lot of the experimental details are not shown. I note in Fig. 2 panel G that there is a significant reduction in the growth rate of the organism as pCO2 increased. Growth rate is strongly tied to the ecological success of an organism. In the real world where there are grazers eating them the reduced growth rate under elevated pCO2 will be a significant disadvantage and may prevent them from reaching a large population size. As a result even though the amount of carbonate per lith increases with increasing pCO2 the overall flux to the seafloor might be significantly reduced. I think the conclusion of the study could the opposite of what the authors say…. At the physical chemical level it is well estabilished that calcification is a function of saturation state (omega). Maybe some coccolithophorid species are different but if they are why? The authors don’t offer any explanations for this surprising result.
2) In my 2005 paper Langdon and Atkinson in J. of Geophysical Research I review all the coral data sets. All species studied have shown a decline in calcification with increasing pCo2. There are differences in sensitivity but all show a decline.
Richard A. Feely, a scientist at NOAA’s Pacific Marine Environmental Lab in Seattle, Wa., said that the widely varied responses of different plankton species to the chemical shifts could portend substantial changes in ocean ecology in a world with far more CO2:
I think this paper, and a few others like it that have been published in recent years, indicate that the response of differernt coccolithophore species to changing CO2 is species dependent and more studies will be required to determine how these responses from different species might cause a shift in species abundances in the oceans and the ecosystem as a whole. For example, with some species of coccolithophores increasing in abundance at the expense of others, the ocean ecosystem might shift towards species that carry more carbon away from the surface and into the ocean interior, causing greater uptake of carbon into the oceans (See Langer et al., 2007). We will need to study more coccolithophore species in the laboratory and field for longer duration experiments to be sure about the long-term response. sourceMy comment: This was the more scientific part of the article. But it says more or less what I was thinking- the study simply doesn't give too much information about the process and the reasons behind it. Not to mention the experimental data! Well, it's obviously quite interesting.