Abstract
Abstract. Specimens of the patellogastropod limpet Patella caerulea were collected within (pHlow-shells) and outside (pHn-shells) a CO2 vent site at Ischia, Italy. Four pHlow-shells and four pHn-shells were sectioned transversally and scanned for polymorph distribution by means of confocal Raman microscopy. The pHlow-shells displayed a twofold increase in aragonite area fraction and size-normalised aragonite area. Size-normalised calcite area was halved in pHlow-shells. Taken together with the increased apical and the decreased flank size-normalised thickness of the pHlow-shells, these data led us to conclude that low-pH-exposed P. caerulea specimens counteract shell dissolution by enhanced shell production. This is different from normal elongation growth and proceeds through addition of aragonitic parts only, while the production of calcitic parts is confined to elongation growth. Therefore, aragonite cannot be regarded as a disadvantageous polymorph per se under ocean acidification conditions.
Highlights
There is general consensus that anthropogenic CO2 emissions lead to decreasing surface ocean pH and carbonate ion concentration, a process termed ocean acidification (e.g. Royal Society, 2005)
This entails a decrease in seawater saturation state with respect to calcium carbonate
Our observations suggest that P. caerulea counteracts this thinning by depositing additional layers on the inner side of the shell
Summary
There is general consensus that anthropogenic CO2 emissions lead to decreasing surface ocean pH and carbonate ion concentration, a process termed ocean acidification (e.g. Royal Society, 2005). It was argued that calcitic shell layers are an adaptation to resist dissolution (Taylor and Reid, 1990) This hypothesis was questioned on the basis of a comparative dissolution study using aragonitic and calcitic bivalve microstructures (Harper, 2000). Comparing the post-mortem dissolution rates of four (two aragonitic and two calcitic) Antarctic benthic species, McClintock et al (2009) supported the conclusion of Harper (2000). These two studies imply the notion that dissolution of calcium carbonate biominerals is not primarily a question of the polymorph, but depends largely on composition and microstructure of the biomineral.
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