Is there a bias between contemporary and subfossil cladoceran assemblages?

Sediment and water samples differ in both temporal and spatial resolution. In this study, we compare a set of contemporary cladoceran samples covering the past 30 years with a subfossil sedimentary sequence from a surficial core spanning the same period. More species were found in the sediment than in the water samples. This result reflects the accumulative and integrative consequences of sedimentation processes. For example, Alona quadrangularis, Alona affinis, Pleuroxus truncatus and Tretocephala ambigua were only found in the sedimentary sequence. In contrast, species occurring frequently in contemporary samples, such as Simocephalus vetulus, were not found in the sediment because their remains are poorly preserved. Ordination analyses (a CA for contemporary samples and a PCA for sediment samples) were performed to investigate the patterns and variation of cladoceran species abundances in both data sets. The application of a Procrustes rotation and PROTEST permutation test to the ordinations (CA and PCA) of these two sets of samples demonstrated that the two sets were significantly similar. However, the number of samples analysed to obtain the same integrating characterisation of the lake community must be much greater if we use live collections rather than sediment samples. This study evidenced the role of lake sediment as an important library for species information and highlighted the potential role of palaeolimnological approaches in biodiversity studies.