The significance of molluscs as paleoecological indicators of freshwater systems in central-western Argentina

DE FRANCESCO, CLAUDIO G.; HASSAN, GABRIELA S.; BERNAVA GUSTAVO VICENTE

PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY

ELSEVIER SCIENCE BV

Año: 2009 vol. 274 p. 105 - 113

0031-0182

The objectives of this study were to (a) analyze the distribution pattern of molluscs in freshwater systems from central-western Argentina, (b) investigate the key environmental factors affecting the species distribution, and (c) compare Quaternary and modern mollusc assemblages in order to evaluate the extent and limitations of freshwater molluscs as paleobioindicators. A total of 45 freshwater habitats were sampled for living molluscs. At each selected site, physical and chemical parameters were quantified, and living molluscs collected. Principal Component Analysis (PCA) was used for the ordination of sampling sites based on environmental variables. To explore the relationships between environmental variables and mollusc assemblages, a Canonical Correspondence Analysis (CCA) was performed. Data on fossil mollusc assemblages from three Quaternary alluvial successions outcropping in the area were combined with the modern data set by means of a Detrended Correspondence Analysis (DCA). Eight taxa were identified: Lymnaea viator, Heleobia hatcheri, Heleobia parchappii, Heleobia aff. parchappii, Chilina mendozana, Biomphalaria peregrina, Physa acuta, and a bivalve attributed to the family Sphaeriidae. Except for H. hatcheri and P. acuta, the species were also recorded as fossils in the area. Overall, the occurrence of molluscs in central-western Argentina appeared to be related to calm vegetated shallow water bodies. With the exception of H. parchappii that only occurred in saline waters (8-16 mS cm- 1), the mollusc assemblages were restricted to low salinities (below 1.9 mS cm- 1). Two main groups, indicative of different energetic environmental conditions related to the stability of the flow regime, were recognized: (1) L. viator, P. acuta, and B. peregrina occurred at lentic habitats (shallow lakes) or calm backwaters (pools) within lotic systems such as streams and rivers, (2) H. hatcheri, H. aff. parchappii, C. mendozana, and Sphaeriidae dominated in lotic habitats where a directional water flow exists. These same groups were recognized in the fossil record allowing the reconstruction of habitats that differed in the magnitude of the water flow. © 2009 Elsevier B.V. All rights reserved.