Effect of sample size and resolution on palaeomalacological interpretation: a case study from Holocene calcareous-fen deposits

This study investigates the effects of sample volume, resolution and accumulation time on the interpretation of a mollusc record from terrestrial deposits. We tested (i) if, and to what extent, small sample sizes impoverish the reconstructed mollusc species richness, and (ii) whether fine-resolution sampling is worth the effort. We analysed three mollusc sequences, covering continuously the entire Holocene, which were collected in a tufa-forming spring fen and differed in sample size and resolution. More than 36 000 specimens of 76 species were processed. Using a rarefaction method, we observed that different sample volumes had a significant effect on the recorded species richness in this type of environment, and 100-cm(3) samples seemed to be sufficient for a reliable reconstruction in tufa deposits. Although the thickness of the sampled layers had no influence on the palaeoecological interpretation, we observed a shift in the mollusc diversity peak once different resolutions were applied. Furthermore, the layers of finer resolution allowed detailed radiocarbon dating and better understanding of trends in species dynamics. We also observed significant confounding relationships among the number of species, number of specimens and accumulation time that can be disentangled if a precise depth-age model is available. (C) 2017 John Wiley & Sons, Ltd.