How does rising atmospheric CO2 affect marine organisms?

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Bryozoan Responses to Naturally Acidified Seawater
Rodolfo-Metalpa, R., Lombardi, C., Cocito, S., Hall-Spencer, J.M. and Gambi, M.C. 2010. Effects of ocean acidification and high temperatures on the bryozoan Myriapora truncata at natural CO2 vents. Marine Ecology 31: 447-456.

Bryozoans or "moss animals" are a geologically important group of small animals that resemble corals and are major calcifiers that are found on rocky shores in cool-water areas of the planet, where they comprise a significant component of the carbonate sediments in shallow sublittoral habitats, and where they form long-lived three-dimensional structures that provide attachment sites for numerous epifauna and trap sediment and food for a variety of infauna.

What was done
In what they describe as "the first coastal transplant experiment designed to investigate the effects of naturally acidified seawater on the rates of net calcification and dissolution of the branched calcitic bryozoan Myriapora truncata," the authors transplanted colonies of the species to normal (pH 8.1), high (pH 7.66) and extremely high (pH 7.43) CO2 conditions at gas vents located just off Italy's Ischia Island in the Tyrrhenian Sea, where they calculated the net calcification rates of live colonies and the dissolution rates of dead colonies by weighing them before and after 45 days of in situ residence in May-June (when seawater temperatures ranged from 19 to 24°C) and after 128 days of in situ residence in July-October (when seawater temperatures ranged from 25-28°C).

What was learned
Rodolfo-Metalpa et al. report that throughout the first and cooler observation period, "dead M. truncata colonies dissolved at high CO2 levels (pH 7.66), whereas live specimens maintained the same net calcification rate as those growing at normal pH." At the extremely high CO2 level, however, the net calcification rate of the live specimens was reduced to only about 20% of what it was at normal pH, but life continued. Throughout the second and warmer observation period, on the other hand, calcification ceased in both the normal and the high CO2 treatments; and in the extremely high CO2 treatment, the transplants died.

What it means
The five scientists conclude that "at moderate temperatures," such as those to which they are currently adapted, "adult M. truncata are able to up-regulate their calcification rates and survive in areas with higher levels of pCO2 than are predicted to occur due to anthropogenic ocean acidification [italics added], although this ability broke down below mean pH 7.4." This latter level, however, is far below what even the IPCC predicts will occur in response to continued burning of fossil fuels, and extremely far below what the more realistic analysis of Tans (2009) suggests. Thus, it would appear that earth's bryozoans likely have little to fear from the continued burning of fossil fuels.

Tans, P. 2009. An accounting of the observed increase in oceanic and atmospheric CO2 and an outlook for the future. Oceanography 22: 26-35.

Reviewed 1 December 2010