Abstract
Shelled pteropods are widely regarded as bioindicators for ocean acidification, because their fragile aragonite shells are susceptible to increasing ocean acidity. While short-term incubations have demonstrated that pteropod calcification is negatively impacted by ocean acidification, we know little about net calcification in response to varying ocean conditions in natural populations. Here, we examine in situ calcification of Limacina helicina pteropods collected from the California Current Ecosystem, a coastal upwelling system with strong spatial gradients in ocean carbonate chemistry, dissolved oxygen and temperature. Depth-averaged pH ranged from 8.03 in warmer offshore waters to 7.77 in cold CO2-rich waters nearshore. Based on high-resolution micro-CT technology, we showed that shell thickness declined by ~ 37% along the upwelling gradient from offshore to nearshore water. Dissolution marks covered only ~ 2% of the shell surface area and were not associated with the observed variation in shell thickness. We thus infer that pteropods make thinner shells where upwelling brings more acidified and colder waters to the surface. Probably the thinner shells do not result from enhanced dissolution, but are due to a decline in calcification. Reduced calcification of pteropods is likely to have major ecological and biogeochemical implications for the cycling of calcium carbonate in the oceans.
Highlights
Shelled pteropods are widely regarded as bioindicators for ocean acidification, because their fragile aragonite shells are susceptible to increasing ocean acidity
Because a recent study using particle tracking demonstrated sustained retention for 5–6 weeks in the coastal regions of the Current Ecosystem (CCE) during the upwelling season[17], we considered the in situ oceanographic variables measured at the time and place of pteropod collection to be representative of the conditions they experienced during most of their lifetime
Based on a combination of micro-CT scans, Scanning Electron Microscopy (SEM) images, and in situ ocean chemistry observations, we found that pteropods produce thinner shells in coastal waters of the CCE than further offshore
Summary
Shelled pteropods are widely regarded as bioindicators for ocean acidification, because their fragile aragonite shells are susceptible to increasing ocean acidity. Ocean acidification is accompanied by lower carbonate ion concentrations, and decreasing saturation states of aragonite and calcite. This will have important consequences for a wide variety of marine organisms, those that produce carbonate shells or skeletons, such as coccolithophores, foraminifers, molluscs, and c orals[6,7,8,9,10,11,12]. Pteropods require a positive balance between precipitation and dissolution processes to form a shell This balance will determine basic shell characteristics, such as growth and thickness, and depends on the environmental conditions pteropods experience during their lifetime[19]. Shell thickness has been proposed as a useful indicator of the effect of environmental change across various temporal scales[26,27]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
