How does rising atmospheric CO2 affect marine organisms?

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Volume 3 Number 11:  1 June 2000

How Do Human Activities Affect Earth's Climate?: Two new studies of the climatic effects of anthropogenic aerosols over the Indian Ocean reveal substantial warming and cooling influences.  A commentary on their implications suggests that "unfortunately for those who would like a quick and accurate assessment of anthropogenic climate forcing over the industrial period, the studies … demonstrate that there is much to be learned before such an assessment can confidently be given."   Put more simply, we don't yet know whether the net effect of all of man's activities tend to warm or cool the planet.

Journal Reviews
The Greenland Ice Sheet and Sea Level Rise of the Last Interglacial: New estimates of the Greenland ice sheet's contribution to sea level rise during the previous interglacial suggest that this ice sheet was a major contributor to the 5 to 6 meter higher-than-present sea level stand.  The results of these new estimates suggest that a future collapse of the West Antarctic ice sheet is exaggerated.

The Future of Coral Reefs: In a review of real and potential anthropogenic impacts on coral reefs, the author concludes that the most serious are the local direct effects of human influence.  He also concludes that the impacts of potential climate change may be greater on terrestrial ecosystems than on oceanic ones.

Drilling for Oil, Finding Corals: A species of cold-water coral listed as endangered has recently been found to be thriving on oil rigs in a part of the world where it has never before been seen and in environmental conditions that would normally lead to its demise.

Coral Bleaching a Result of Increased El Niño Activity?: The authors put forward the hypothesis that the recent apparent increase in mass coral reef bleaching events is driven by the 3- to 4-year El Niño cycle that rides upon the background of pervasive global warming.

A Quarter-Century of Mollusc History in French Polynesia: Twenty-five years of human and natural disturbances, including periodic coral bleaching, greatly diminished mullosc species richness on a fringing reef of a volcanic island in French Polynesia; but they had no impact on the species richness of a barrier reef located further from the island, where there was less direct human involvement with the mulloscs.

Effects of Elevated CO2 on Photosynthesis and Growth of Three C4 Species: After approximately 40 days of atmospheric CO2 enrichment, three well-watered C4 species, differing in rates of CO2-leakage from their bundle sheath cells, all displayed 10 to 24% increases in their photosynthetic rates independent of their CO2-leakage rates without modifying enzymatic activity of rubisco or PEP-carboxylase.  However, these CO2-induced photosynthetic enhancements lead to a significant biomass increase (+50%) in only one of the three tested species.  Nonetheless, these results indicate that atmospheric CO2 enrichment can directly stimulate photosynthesis and growth in C4 plant species.

Effects of Elevated CO2 on an Important C4 Crop: Maize: After approximately 30 days of atmospheric CO2 enrichment, well-watered maize (a C4 crop) exhibited significantly greater rates of net photosynthesis and total biomass production than did plants grown at ambient CO2.  In addition, elevated CO2 reduced leaf stomatal density and stomatal conductance, thereby increasing the water-use efficiency of the CO2-enriched maize plants by over 225% relative to that observed in control plants.  This paper thus provides further evidence for the direct positive effects of elevated CO2 on C4 plant photosynthesis and growth.

Effects of Elevated CO2 on Nectar Production in Nasturtiums: After nearly 80 days of atmospheric CO2 enrichment, nasturtiums grown at 760 ppm CO2 displayed 35% more total biomass than plants grown at 380 ppm CO2, although the elevated CO2 did not cause any specific increases in reproductive biomass.  Nonetheless, flowers produced in elevated CO2 produced nearly two and a half times more nectar than flowers on plants grown in ambient CO2 without affecting nectar quality, i.e., sugar and amino acid content and composition.

Effects of CO2 and O2 Concentrations on a Seaweed: After three weeks of exposure to a doubled atmospheric CO2 concentration, the red seaweed, Lomentaria articulata, exhibited 52 and 314% greater daily net carbon gains and wet biomass production than control plants grown at ambient CO2.  Even under an elevated CO2 concentration that was 500% greater than ambient, CO2-enriched seaweed still maintained daily net carbon gains and wet biomass production rates that were 23 and 50% greater, respectively, than those of ambiently-grown seaweed.  Thus, aquatic plants will likely benefit from further increases in the CO2 content of the air, as do most terrestrial plants.

Effects of Elevated CO2 on Wood Properties and Ring Width of Pine: After four years of atmospheric CO2 enrichment within open-top chambers, loblolly pine seedlings exposed to 650 ppm CO2 exhibited significantly greater annual growth-ring widths than those produced by seedlings grown at 350 ppm CO2.  Additionally, ring densities tended to be greater for CO2-enriched seedlings during each year of the study.  Thus, it is likely that future increases in the air's CO2 content will increase loblolly pine wood production, while maintaining or increasing the wood's structural integrity.