Phytoplankton Calcification in a High-CO ₂ World

Abstract

Ocean acidification in response to rising atmospheric CO2 partial pressures is widely expected to reduce calcification by marine organisms. From the mid-Mesozoic, coccolithophores have been major calcium carbonate producers in the world's oceans, today accounting for about a third of the total marine CaCO3 production. Here, we present laboratory evidence that calcification and net primary production in the coccolithophore species Emiliania huxleyi are significantly increased by high CO2 partial pressures. Field evidence from the deep ocean is consistent with these laboratory conclusions, indicating that over the past 220 years there has been a 40% increase in average coccolith mass. Our findings show that coccolithophores are already responding and will probably continue to respond to rising atmospheric CO2 partial pressures, which has important implications for biogeochemical modeling of future oceans and climate.

A safe operating space for humanity

“…The projected rate of change in ocean CO 2 chemistry leaves little time for organisms to evolve adaptations. While some species may be CO 2 -insensitive or able to adapt (e.g., Miller et al, 2009), the energetic costs of achieving net shell growth and preventing dissolution in conditions of aragonite under-saturation will likely have other impacts on overall growth rates, predation, metabolism or reproduction, as observed in organisms from other regions (e.g., Iglesias-Rodriguez et al, 2008;Fabry et al, 2008;Wood et al, 2008;Tunnicliffe et al, 2009).…”

Photosynthetic responses of <i>Emiliania huxleyi</i> to UV radiation and elevated temperature: roles of calcified coccoliths

“…Many studies focused on the effects of ocean acidification on coccolithophore (Riebesell et al, 2000;Feng et al, 2008;Iglesias-Rodriguez et al, 2008;De Bodt et al, 2010), but few considered the role of UVR in natural conditions (Gao et al, 2009). Our results indicate that reduced calcification in E. huxleyi made the cells more vulnerable when they are exposed to excessive light energy even without UVR considered, since reduced calcification led to downregualated photoprotective capability.…”

Will ocean acidification affect marine microbes?

“…For example, a number of studies have investigated the consequences of reduced pH for calcifying phytoplankton (Table 1). Results by a number of laboratories suggest negative effects of higher CO 2 /lower pH on coccolithophore cultures (Riebesell et al, 2000(Riebesell et al, , 2007 but at least two studies indicate enhanced calcification under elevated CO 2 (Langer et al, 2006;Iglesias-Rodriguez et al, 2008). Ridgwell et al (2009) have suggested that some of these differences may be due to strain variations in the cultures used for these experiments; or there may be experimental design consequences resulting from the procedures used to adjust the pH .…”