Apparently, long-term coral growth rates are not related to CO2 levels.

By: hcubed , 2:11 PM GMT on October 26, 2011

Peer-reviewed Paper here (paywalled, of course):

Acclimation to ocean acidification during long-term CO2 exposure in the cold-water coral Lophelia pertusa


Abstract:

"...Ocean acidity has increased by 30% since preindustrial times due to the uptake of anthropogenic CO2 and is projected to rise by another 120% before 2100 if CO2 emissions continue at current rates. Ocean acidification is expected to have wide-ranging impacts on marine life, including reduced growth and net erosion of coral reefs. Our present understanding of the impacts of ocean acidification on marine life, however, relies heavily on results from short-term CO2 perturbation studies. Here we present results from the first long-term CO2 perturbation study on the dominant reef-building cold-water coral Lophelia pertusa and relate them to results from a short-term study to compare the effect of exposure time on the coral's responses. Short-term (one week) high CO2 exposure resulted in a decline of calcification by 26-29% for a pH decrease of 0.1 units and net dissolution of calcium carbonate. In contrast, L. pertusa was capable to acclimate to acidified conditions in long-term (six months) incubations, leading to even slightly enhanced rates of calcification. Net growth is sustained even in waters sub-saturated with respect to aragonite. Acclimation to seawater acidification did not cause a measurable increase in metabolic rates. This is the first evidence of successful acclimation in a coral species to ocean acidification, emphasizing the general need for long-term incubations in ocean acidification research. To conclude on the sensitivity of cold-water coral reefs to future ocean acidification further ecophysiological studies are necessary which should also encompass the role of food availability and rising temperatures..."

One key statement from the paper was:

"...Growth rates in the long-term experiment (LTE) did not follow the negative trend with increasing pCO2 observed in the short-term incubation. Instead, growth rate, which was comparable to that of the control treatment in the short-term experiment, stayed high at elevated CO2 levels...There was no statistically significant relationship between average growth rates and pCO2 concentrations..."

Even though they raised atmospheric CO2 to levels roughly equal to 981 ppmv, they did see a loss in short term growth, but a gain in long term growth.

They also discovered something else, long known to fish tank owners - the life in the tank has more of an effect on the water's pH levels than the atmosphere does:

"...At the beginning, all CRS [the "closed recirculating systems" containing the coral] were supplied with ambient air with a pCO2 level of approx. 406 µatm. After taking water samples for TA [total alkalinity], DIC [dissolved inorganic carbon], and nutrients and measurements of the physicochemical water parameters (temperature, pH, salinity), sampling, the physicochemical parameters (salinity, pH, temperature) of each reactor were monitored by inserting a multi sensor device (Multi350i, WTW) into a small opening in the lid. During incubations, pH and pCO2 [partial pressure of CO2] can change differently in each bioreactor depending on rates of respiration and calcification of the enclosed coral branches. Therefore, the carbonate system parameters (pH, pCO2, ΩAr) and growth rates were calculated separately for each bioreactor..."

It appears that more long term studies are needed, and "...should also encompass the role of food availability and rising temperatures..."

Not just CO2...


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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Living in Biloxi MS, have been here since '85 (first Hurricane was Elena).

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