Shellfish Face Uncertain Future in High CO2 World: Influence of Acidification on Oyster Larvae Calcification and Growth in Estuaries

Abstract

BackgroundHuman activities have increased atmospheric concentrations of carbon dioxide by 36% during the past 200 years. One third of all anthropogenic CO2 has been absorbed by the oceans, reducing pH by about 0.1 of a unit and significantly altering their carbonate chemistry. There is widespread concern that these changes are altering marine habitats severely, but little or no attention has been given to the biota of estuarine and coastal settings, ecosystems that are less pH buffered because of naturally reduced alkalinity.Methodology/Principal FindingsTo address CO2-induced changes to estuarine calcification, veliger larvae of two oyster species, the Eastern oyster (Crassostrea virginica), and the Suminoe oyster (Crassostrea ariakensis) were grown in estuarine water under four pCO2 regimes, 280, 380, 560 and 800 µatm, to simulate atmospheric conditions in the pre-industrial era, present, and projected future concentrations in 50 and 100 years respectively. CO2 manipulations were made using an automated negative feedback control system that allowed continuous and precise control over the pCO2 in experimental aquaria. Larval growth was measured using image analysis, and calcification was measured by chemical analysis of calcium in their shells. C. virginica experienced a 16% decrease in shell area and a 42% reduction in calcium content when pre-industrial and end of 21st century pCO2 treatments were compared. C. ariakensis showed no change to either growth or calcification. Both species demonstrated net calcification and growth, even when aragonite was undersaturated, a result that runs counter to previous expectations for invertebrate larvae that produce aragonite shells.Conclusions and SignificanceOur results suggest that temperate estuarine and coastal ecosystems are vulnerable to the expected changes in water chemistry due to elevated atmospheric CO2 and that biological responses to acidification, especially calcifying biota, will be species-specific and therefore much more variable and complex than reported previously.

A safe operating space for humanity

“…arag of 3.44. Recognizing that carbonate chemistry can be variable over diel and seasonal timescales Feely et al, 2008;Miller et al, 2009), we suggest that the typical diel and seasonal range of values of aragonite saturation state be incorporated into this boundary (i.e., > 80% of the average surface ocean, preindustrial aragonite saturation state +/-diel and seasonal variability). The major rationale behind this subjective value is twofold: to keep high-latitude surface waters above aragonite under-saturation and to ensure adequate conditions for most coral systems.…”

“…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).…”

Ocean acidification and temperature rise: effects on calcification during early development of the cuttlefish Sepia officinalis

“…Numerous studies on bivalve molluscs showed reduced rates of calcification in response to ocean acidification (e.g. Miller et al 2009;. Marine organisms display a species-specific ability to calcify (Ries et al 2009, Findlay et al 2011, probably linked to their ability to maintain favorable chemical condition for CaCO 3 precipitation at the calcification site when exposed to high pCO 2 (e.g.…”

Effects of ocean acidification on immune responses of the Pacific oyster Crassostrea gigas

“…Previous studies have found that OA stress impaired the energy metabolic pathways in oysters, and also retarded the normal growth and development [23,24]. However, the impact of OA on the immune responses of oysters has received little attention so far.…”