Morphological Properties of Gastropod Shells in a Warmer and More Acidic Future Ocean Using 3D Micro-Computed Tomography

Eva Chatzinikolaou,Panos Grigoriou,Kleoniki Keklikoglou

doi:10.3389/fmars.2021.645660

Eva Chatzinikolaou, Panos Grigoriou + Show 1 more

Open Access

https://doi.org/10.3389/fmars.2021.645660

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Abstract

The increased absorption of atmospheric CO2 by the ocean reduces pH and affects the carbonate chemistry of seawater, thus interfering with the shell formation processes of marine calcifiers. The present study aims to examine the effects of ocean acidification and warming on the shell morphological properties of two intertidal gastropod species, Nassarius nitidus and Columbella rustica. The experimental treatments lasted for 3 months and combined a temperature increase of 3°C and a pH reduction of 0.3 units. The selected treatments reflected the high emissions (RCP 8.5) “business as usual” scenario of the Intergovernmental Panel on Climate Change models for eastern Mediterranean. The morphological and architectural properties of the shell, such as density, thickness and porosity were examined using 3D micro-computed tomography, which is a technique giving the advantage of calculating values for the total shell (not only at specific points) and at the same time leaving the shells intact. Nassarius nitidus had a lower shell density and thickness and a higher porosity when the pH was reduced at ambient temperature, but the combination of reduced pH and increased temperature did not have a noticeable effect in comparison to the control. The shell of Columbella rustica was less dense, thinner and more porous under acidic and warm conditions, but when the temperature was increased under ambient pH the shells were thicker and denser than the control. Under low pH and ambient temperature, shells showed no differences compared to the control. The vulnerability of calcareous shells to ocean acidification and warming appears to be variable among species. Plasticity of shell building organisms as an acclimation action toward a continuously changing marine environment needs to be further investigated focusing on species or shell region specific adaptation mechanisms.

Highlights

The last three decades were the warmest period of the last 1,400 years in the Northern Hemisphere of the planet (IPCC, 2014)
The increased variability observed between individuals and the relatively low number of specimens due to the logistical constraints of performing a micro-CT analysis could possibly be the reason for this limited statistical significance; the observed trends can still offer a useful insight in shell architecture of N. nitidus and the respective data presented in Figure 1 are being further described
The combination of low pH and warm temperature (7W) was not detrimental for N. nitidus since the respective values were more similar to the control (8A)

Summary

Introduction

The last three decades were the warmest period of the last 1,400 years in the Northern Hemisphere of the planet (IPCC, 2014). The upper 75 m of the sea surface have been experiencing strongest warming (0.11◦C per decade) over the period 1971 to 2010 (IPCC, 2014). The dissolution of particulate organic carbon in the ocean affects the calcification rates of organisms, which are predicted to decrease by 40% until 2100 if anthropogenic CO2 emissions are not reduced (Andersson et al, 2006). The impacts of ocean acidification may be first witnessed in coastal ecosystems which express higher variability in carbonate chemistry and are more unstable environments compared to the deep sea (Feely et al, 2004; Andersson et al, 2006; Harris et al, 2013)

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