Malacological remains from the Sambaqui da Tarioba (Rio das Ostras – RJ, Brazil): Marine mollusc biodiversity in the recent Holocene

Abstract

The interpretation of archaeological sites of the sambaqui type (Brazilian shell middens) as proxies of past biodiversity is a promising approach. The sambaqui sites were built by prehistoric human populations between 8000 and 1000 BP, and they are extremely abundant on the Brazilian coast and bear information about the existing organisms at the time of their construction. In the current study, inferences about the past biological diversity of molluscs were made based on a profile of 1 m2 with a 1.3 m depth in sector HS-A1-e of the Sambaqui da Tarioba (Rio das Ostras, Rio de Janeiro, Brazil), which was dug in 2012. Sampling sufficiency was found for all five archaeo-stratigraphic layers in the site. The diversity indexes studied (Absolute Richness, Relative Richness, and Shannon and Simpson indexes) showed similar patterns to those of live mollusc communities. Non-parametric Kruskal-Wallis and Mann-Whitney tests did not reveal statistically significant differences in species abundance between layers. The diversity profiles built using the Rényi series showed that the mollusc diversity patterns in the Sambaqui da Tarioba varied along its 550 years of settlement, however, with no statistically significant difference among them. The taxonomic distinctness structure of the malacological diversity inventory for the Sambaqui da Tarioba was similar to a random sampling of the complete list of species currently found in the Rio das Ostras. Therefore, the current results indicate that although the information about biodiversity obtained from sambaqui sites could have some inaccuracy (because they are artificial accumulations), it is still relevant and prone to be accessed.