Detection of periodic Sr Ca−1 cycles along gastropod statoliths allows the accurate estimation of age
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Gastropods retain less obvious periodic growth marks on calcified structures than individuals in other groups (e.g. bivalves, cephalopods, fish), a fact that has hampered age estimation in this Class. Nevertheless, a model of age estimation for the gastropod Nassarius reticulatus is possible based on the annual growth rings deposited in statoliths during the winter. These spherical aragonitic carbonate structures are located inside the statocysts and contain a characteristic microstructural pattern of concentric rings. However, this pattern can be biased by the formation of nonperiodic disturbance rings (DRs). In Aveiro (NW Portugal), an increased frequency of DRs was reported in statoliths of specimens inhabiting the Ria de Aveiro lagoon (a highly dynamic environment), when compared with specimens collected from the relatively environmentally stable adjacent offshore area. One approach to resolve annual growth in organically precipitated carbonates is to find a chemical signature within the microstructure that faithfully records changes in seasonal environmental parameters. In this contribution, we have analysed the Sr Ca−1 variation along statolith sections by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) as a proxy to resolve seasonal cycles of temperature, allowing the identification of annual growth rings. Combining this information with size–frequency distributions of shell height, we found strong evidence that the rings chemically labelled with 88Sr 48Ca−1 peaks are formed annually during the cold season. Hence, LA-ICPMS allows not only the detection of visible rings but also the distinction between rings formed at low temperatures (i.e. a periodic seasonal signature) and those of disturbance (not characterised by increased 88Sr 48Ca−1). There is also clear evidence that the 88Sr 48Ca−1 peaks become less conspicuous from the nucleus to the statolith edge, leading to a loss of discriminatory power for the identification of older age rings. Nevertheless, this new method allows the accurate age estimation of N. reticulatus specimens and is liable to be applied in a wide range of gastropods after specific validation.
KeywordsGrowth Ring Shell Height Laser Ablation Inductively Couple Plasma Mass Spectrometry 88Sr 48Ca Annual Growth Ring
This work was supported by European Funds—through FP7 research infrastructure initiative ASSEMBLE (Grant Agreement No. 227799) and the Operational Competitiveness Programme COMPETE—and by National Funds—through the Portuguese Foundation for Science and Technology projects PEst-C/MAR/LA0017/2013, UID/AMB/50017/2013, and the grant SFRH/BPD/70368/2010 (supported by funding from the Human Potential Operational Programme POPH, inscribed in the National Strategic Reference Framework and partially subsidised by the European Social Fund). The authors thank the Scottish Association of Marine Science for hosting project BIOREC under ASSEMBLE EU FP7-RI, and the colleagues Filipe Laranjeiro, Inês Louro, Inês Silva, Pedro Aires, Ruy Santos—for their assistance during sampling and specimens measuring for the SH-frequency distribution study—and Fábio Matos for his assistance with the R programming language.
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