Volume 11, Number 7: 13 February 2008
In a fascinating study that appeared as the lead article of volume 344 of the scientific journal Marine Ecology Progress Series, Palacios and Zimmerman (2007) describe a unique experiment they conducted at the Duke Energy-North America Power Plant at Moss Landing, California (USA), where flue gas generated by the power plant furnace was piped approximately 1 km to a site where it was bubbled through outdoor flow-through seawater aquaria at rates that produced four different aqueous CO2 treatments characteristic of: "(1) the present day atmosphere, with approximately 16 然 CO2(aq), (2) CO2 projected for 2100 that increases the CO2(aq) concentration of seawater to approximately 36 然 CO2(aq), (3) CO2 projected for 2200 that increases the CO2(aq) concentration of seawater to 85 然 CO2(aq), and (4) a dissolved aqueous CO2 concentration of 1123 然 CO2(aq), which triples the light-saturated photosynthesis rate of eelgrass (Zimmerman et al., 1997)."
So what did this unique experiment reveal?
The researchers report that the elevated CO2 "led to significantly higher reproductive output, below-ground biomass and vegetative proliferation of new shoots in light-replete treatments," i.e., those receiving light at 33% of the surface irradiance level. More specifically, they write that "shoots growing at 36 然 CO2(aq) were 25% larger than those in the unenriched treatment [16 然 CO2(aq)]," while "at 85 然 CO2(aq) shoots were 50% larger than those in the unenriched treatment and at 1123 然 CO2(aq) shoots were almost twice as large as those in the unenriched treatment." In addition, they found that at 1123 然 CO2(aq) "22% of the shoots differentiated into flowers, more than twice the flowering output of the other treatments at this light level."
These findings are of great significance and have far-reaching implications. Noting that "increased CO2(aq) is capable of increasing eelgrass reproductive output via flowering, and area-specific productivity via vegetative shoot proliferation under naturally replete light regimes," Palacios and Zimmerman state that "the resulting increases in eelgrass meadow density may initiate a positive feedback loop that facilitates the trapping of sediments and prevents their resuspension, thereby reducing turbidity and increasing light penetration in coastal habitats," such that the resulting increased light penetration "may allow seagrass colonization depths to increase even further."
The two researchers also suggest that the CO2-induced increase in the productivity of eelgrass may "enhance fish and invertebrate stocks as well." In fact, they go so far as to suggest that the "deliberate injection [our italics] of CO2 to seawater may facilitate restoration efforts by improving the survival rates of recently transplanted eelgrass shoots," noting that "it can buffer the negative effects of transplant shock by increasing rhizome reserve capacity and promoting shoot proliferation in light-replete environments." In addition, they say it "may also facilitate eelgrass survival in environments where conditions are periodically limiting, such as long dark winters or unusually warm summers that produce unfavorable productivity to respiration ratios," and they state that "CO2 injection may also promote flowering and seed production necessary for expansion and maintenance of healthy eelgrass meadows." What is more, they suggest that "rising concentrations of CO2(aq) may increase vegetative propagation and seed production of other seagrass populations besides eelgrass."
All in all, it would appear that the ongoing rise in the atmosphere's CO2 concentration bodes well indeed for earth's seagrasses, so well, in fact, that Palacios and Zimmerman are even suggesting direct injections of power-plant flue gas along coastlines in an effort to improve the establishment and expansion of seagrass meadows and the benefits to coastal marine ecosystems that typically accompany them.
Sherwood, Keith and Craig Idso
References
Palacios, S.L. and Zimmerman, R.C. 2007. Response of eelgrass Zostera marina to CO2 enrichment: possible impacts of climate change and potential for remediation of coastal habitats. Marine Ecology Progress Series 344: 1-13.
Zimmerman, R.C., Kohrs, D.G., Steller, D.L. and Alberte, R.S. 1997. Impacts of CO2-enrichment on productivity and light requirements of eelgrass. Plant Physiology 115: 599-607.